David Defour - Université de Perpignan

jeudi 26 janvier 12 

PROGRAMMATION SOUS 

ANDROID 

David Defour 

Université de Perpignan 

Originals of Slides and Source Code for Examples: 

http://www.coreservlets.com/android-tutorial/

• Equipements 

• Salle machine avec: 

ORGANISATIONS 

• 2 tablettes ACER Iconia A500 sous Android 3.2 (Honeycomb) 

• 2 tablettes Archos Internet Tablet 70 sous Android 2.2 (Froyo) 

• Au sujet de ce module 

• 9h de CM (6 x 1h 30) 

• 21h de TDO (7 x 3h) 

• Note pour l’UE : Projet final + soutenance 

• Terminologie 


A vos Machines


DESCRIPTION DU PROJET

• Honnêteté intellectuelle 

RECOMMANDATIONS 

• Toutes parties de code, texte, algorithmes, ... qui n’est pas de vous et dont la référence n’est pas clairement 

indiquée conduira à un ZERO 

• Commentaires 

• Le programme devra être clairement structuré (décrit dans le rapport) et commenté (utilisation de 

javadoc et d’éclipse) 

• Délai 

• Le projet devra impérativement être rendu avant le 31 mars 2012 

• Sujets 


• Un sujet vous est proposé par défaut, 

• En accord avec le responsable du cours il est possible de proposer un autre sujet avant le 15 février 2012

DESCRIPTION 

• Titre : Réalisation d’une interface en drag-&-drop d’un 

interpréteur de langage Logo sur le modèle de App Inventors 

• Objectifs 


• Rendre possible la programmation sur un périphérique 

Android 

• Programmer sans clavier 

(Attention: c’est une condition importante dans ce projet, il 

faut minimiser son usage)

DESCRIPTION DE L’INTERFACE 

• Fenêtre d’édition divisée en 2 parties 

• Une boite à objet avec des boites symbolisant les briques de base du langage pour 

faire bouger la tortue 

• Une zone de programmation 

• Un interpréteur de votre langage pour visualiser le résultat 

• Fonctionnalités supplémentaires 


• Bouton «save», «load», «do», «undo», «debug», «help», «procédures», «copy/paste» 

• Gestion des erreurs


EXAMPLE: APP INVENTOR

• Déplacements 

• Gestion du trait 

STRUCTURATION DU 

• Gestion du contrôle 


LANGAGE


DÉPLACEMENTS 

Ordre Fonctions 

AV n Commande à la tortue d’avancer de n pas 

TD n Commande à la tortue d’effectuer une rotation de n degrés à droite 

TG n Commande à la tortue d’effectuer une rotation de n degrés à gauche 

REC n Commande à la tortue de reculer de n pas 

FPOS [n1 n2] Place la tortue à la position (n1,n2) de l’écran 

FCAP n Fixe le cap de la tortue


GESTION DU TRAIT 


VE Efface l’écran 

MT Rend la tortue visible 

CT Rend la tortue invisible à l’utilisateur 

LC Demande à la tortue de lever le crayon 

BC Demande à la tortue de baisser le crayon 

FCC n Fixe la couleur du crayon de la tortue

GESTION DU CONTRÔLE 


REPETE n [ liste ] Répète n fois les instructions contenues dans la liste 

HASARD n Renvoie un nombre compris entre 0 et n 

CAP Renvoie le cap de la tortue 

LOOP Renvoie le nombre de fois que l’instruction REPETE a été exécutée 

SI predicat 

[ liste 1] [ liste2 ] 

Si prédicat est vrai, exécute les instructions de liste1 sinon celles de liste2. La liste 2 est optionnelle. 

TANQUE exp [liste] Répète les instructions contenues dans liste tant que exp est vrai. 

jeudi 26 janvier 12

LANGAGE, FONCTIONNALITÉS 

• BONUS : 


• Gestions des procédures 

AVANCÉES

RÉFÉRENCES: 

• http://lwh.free.fr/pages/prog/logo/Logo.pdf 

• http://www.appinventorbeta.com/learn/reference/index.html 

jeudi 26 janvier 12

PROGRAMMATION ANDROID: 


PRÉSENTATION 





• Motivations 

RÉSUMÉ DU COURS 

• Web Apps vs. Mobile Apps 

• iPhone Apps vs. Android Apps 

• Livres & Références 

jeudi 26 janvier 12


WEB APPS VS. 

ANDROID APPS

AVANTAGES DES APPLI WEB 

• Accès universel 

• Navigateurs présent partout 

• N’importe quel périphérique connecté 

peu accéder à du contenu 

• PCs, Macs, Linux, Android, 

iPhone, Blackberry, etc. 

• Mise à jour automatique 

• Le contenu vient du serveur => 

toujours à jour 

• Outils et méthodes éprouvées 

• Plusieurs langages 

• Java, PHP, .NET, Ruby/Rails, CGI, etc. 

jeudi 26 janvier 12

INCONVÉNIENTS DES APPLI 

WEB 

• Peu d’Interface HM avec peu de contrôle 

• Textfield, text area, button, checkbox, radio, list box, combo box. c’est tout ! Pas de 

dessin direct (Sauf pour les canvas en HTML5) 

• Ne peut pas interagir avec les ressources locales 

• Impossibilité de lire des fichiers, d’appeler des programmes ou d’accéder aux 

périphériques de la machine 

• Communication inefficace 

• HTTP est un protocole faible 

• Difficulté d’écrite 

• Nécessite des connaissances en plusieurs techno 

• Java, HTML, HTTP, CSS, JavaScript, XML 

• Conçu pour des périphériques avec de grand écran et une souris 

• Plus difficile de les utiliser sur un plus petit téléphone avec écran tactile 

jeudi 26 janvier 12

AVANTAGES DES APPLI 

MOBILES 

• Plusieurs interfaces de contrôles GUI 

• Textfield, text area, button, checkbox, radio, list box, combo box, 

clock, calendar, date picker, dialog box, image gallery, etc. 

• Comparable à la programmation sur PC 

• Supports du dessin direct 

• Les jeux animés de type Angry Birds sont possibles 

• Possibilité d’interagir avec les ressources locales 


• Possibilités de lire les fichiers (ex: liste de contact), BD locale, 

accès au GPS, lancement d’un appel GSM, accès au micro, au 

haut-parleur, lecture de l’orientation de l’écran, etc...

AVANTAGES DES APPS 

MOBILES 

• Communication efficace 

• Possibilité d’utiliser le protocole de communication de votre choix 

• Plus facile à écrire 

• Un seul langage à maîtriser 

• Java pour Android 

• Objective C pour iPhone 

• Conçu pour des périphériques avec de petit écran tactile 

• Les apps et les interfaces GUI sont optimisées pour ce type 

d’environnement 

jeudi 26 janvier 12

INCONVÉNIENTS DES APPS 

• Pas d’accès universel 

MOBILES 

• Les Apps doivent être installées sur chaque périphérique 

• Une apps Android ne fonctionnera pas sur iPhone, Blackberry, 

PC, Mac, où box Linux 

• Gestion des updates difficile 

• L’utilisateur doit intervenir pour installer la dernière version 

• Plus récent (esp. Android) 


• Manque de standard, d’outils et de méthodes établits, 

• ... mais la programmation Android est proche de la 

programmation Java classique qui est elle ancienne.

ANDROID 

APPS 

VS. 

IPHONE APPS 

jeudi 26 janvier 12

INSTALLATION 

• Apps génériques 

• Sélection plus importante pour iPhone 

• Android essaie de se rattraper 

• Apps adhoc pour l’entreprise 

• Les apps iPhone ne peuvent s’installer que via l’App Store 

• Vous devez soumettre votre apps à l’Apple App Store et obtenir leur feu vert, même 

pour des applis privées destinées à votre société. 

• (sauf si vous JailBreaké votre Iphone) 

• Les apps Android peuvent s’installées via : 

• Google App Store 

• Amazon App Store 

• Connexion USB à partir de votre PC 

• Email 

• Votre Site Web 

jeudi 26 janvier 12


LANGUAGES DE PROG 

• iPhone 

• Objective-C 

• Proche du C++, mais pas identique 

• Android 

• Java 

• Langage le + utilisé dans le monde de l’entreprise 

• C/C++ 

• Possibilité d’appeler 

The real reason Android runs Java 

nativement (avec 

difficulté) via une 

approche de type JNI 

From Randall Munroe and xkcd.com

OS POUR LE 

DÉVELOPPEMENT DES APPS 

• iPhone 

• Macs 

• Android 

• Tout ce qui peut installer 

Java et Eclipse 

• Macs 

• PCs 

• Linux 

• Solaris 


From http://www.hongkiat.com/blog/mac-vs-pc-myth-busting-consumer-guide/


PROGRAMMING JOBS: 

ANDROID VS. IPHONE 

• Cadre: Indeed.com ne montre que la tendance 

• Offre d’emploie contenant les 2 mots n’importe où 

• Biaisé par le site de références

GOOGLE SEARCH: ANDROID 


VS. IPHONE PROGRAMMING 

• Cadre: montre la tendance sur les volumes de requête 

• Example: plus de tuto clair pour Android or iPhone implique 

moins de recherche

GAINS LIÉS À LA PUBLICITÉ: 

ANDROID (53%) VS. IPHONE (27%) 


• Cadre: la pub ne correspond pas aux volumes, biaisé par les 

partenaires de Millennial Media


PRÉSENCE SUR LE MARCHÉ 

Cadre: basé sur une étude et non sur des volumes de vente réel. 

Raw data at http://www.comscore.com/Press_Events/Press_Releases/2011/7/comScore_Reports_May_2011_U.S._Mobile_Subscriber_Market_Share

IPHONE VS. ANDROID 

• Lequel utiliser personnellement 

• iPhone a plus de part de marché, un catalogue plus étoffé et 

des utilisateurs plus loyaux 

• Android est plus ouvert et croit plus rapidement 

• Conclusion: pas de vainqueur clair, à vous de voir 

• Lequel choisir si vous avez des apps maisons 


• Plus difficile avec l’iPhone qu’avec Android. 

• iPhone utilise Objective C et Android Java 

• Conclusion: Android est le vainqueur


CONCLUSION 

Présentation

RÉFÉRENCES 

• Livres (Par ordre de préférence) 

• Android Developer’s Cookbook (Steele & To) 

• Busy Coder’s Guide to Android Development (Murphy) 

• En ligne seulement: http://commonsware.com/Android/ 

• Android in Action, 2 nd Edition (Ableson, Sen, & King) 

• Android Application Development for Dummies (Felker) 

• Site web: 

• http://developer.android.com/ 

• De loin la source la plus importante 

• Forum Android sur StackOverflow 

• http://stackoverflow.com/questions/tagged/android 

• La galerie des widget Android 

• http://www.droiddraw.org/widgetguide.html 

jeudi 26 janvier 12

• Web apps vs. Android apps 


RÉSUMÉ 

• Les apps Web fonctionnent sur n’importe quel device mais 

ont une interface GUI faible, ne peuvent utiliser de 

ressources locales (fichiers, BD, GPS, camera) et sont plus 

agréable à utiliser avec un grand écran. 

• Les apps Android peuvent utiliser les ressources locales, sont 

optimisées pour les petits écrans, ont une GUI plus riches, 

mais ne peuvent pas être installé sur d’autres type de device.


QUESTIONS?


ANDROID: INSTALLATION & 

PREMIER DÉMARRAGE 






• Installation des logiciels et de la documentation 

• Java 

• Eclipse 

• Android SDK, base 

• Plugin Eclipse ADT 

• Mise à jour des composants du SDK 

• AVD (Android Virtual Device) 

• Lancement d’une application 


• Importer et tester une application existante 

L’exécuter sur l’émulateur 

• Créer et tester une nouvelle application 

L’exécuter sur l’émulateur 

• Visualiser les sorties standards dans le DDMS 

• Déployer une application sur un périphérique Android connecté en mode USB


INSTALLATION DE LA 

DOCUMENTATION ET DES 

LOGICIELS

• Présentation 


JDK POUR JAVA SE 6 

• Java 6 est la version la plus récente et rapide 

(Java 5 est supporté par Android mais non-recommandé) 

• Pour les PC, Linux : 

• http://www.oracle.com/technetwork/java/javase/downloads/ 

• Télécharger le JDK et pas seulement le JRE 

• Télécharger la SE (Standard Edition), pas la EE ou la ME (Micro Edition) 

• Pas besoin de la version avec l’IDE NetBeans 

• Pour MAC 

• Rien a faire (java est installé et maintenu automatiquement)

INSTALLATION DE JAVA SE 6 

• http://www.oracle.com/technetwork/java/javase/downloads/ 

Use this version. The “JDK – Java 

Development Kit” includes compiler for .java 

files, whereas the “JRE – Java Runtime 

Environment” is only for executing 

prebuilt .class files. 


After downloading, run installer and accept all defaults. 

This tutorial uses Eclipse, so 

do not use this link. 

As of summer 2011, there is 

no NetBeans plugin for 

Android development. So, 

Eclipse is strongly 

recommended even if you 

normally use NetBeans for 

Java development. However, 

IntelliJ IDEA has Android 

support: see 

http://www.jetbrains.com/ 

idea/features/ 

google_android.html


ECLIPSE 

• Eclipse est un IDE libre, opensource. Supporte Java, HTML, CSS, Javascript, C++, PHP, ... 

• Google propose un plugin Eclipse pour l’intégration du SDK Android 

• Fonctionnalités 


• Générales 

• Vérifie la syntaxe lors de la saisie 

• Compilation automatique à chaque sauvegarde 

• Factorisation du code, debbugage, templates 

• Spécifiques à Android 

• Facilite le déploiement d’apps Android vers l’émulateur 

• Configuration d’un environnement virtuel 

• Drag-&-Drop GUI

INSTALLATION D’ECLIPSE 

• http://eclipse.org, puis section “Downloads” 


• Résultats de 

http://eclipse.org/downloads/ 

• Sélectionner “for Java” où 

“for Java EE” (+ apps web) 

• Dernière version (3.6 – Helios) recommandée 

• Avant dernière version (3.5 – Ganymede) encore supportée 

• Versions plus anciennes (3.4 et

LANCER ECLIPSE 

• Dezippez le fichier téléchargé (pas d’installeur!) 

• Renommez le répertoire “installDir” 

• Double clickez sur eclipse.exe 

• A partir de installDir/bin 

• Clickez sur l’icone “Workbench” 

• Au prochain démarrage d’éclipse 

workbench apparaîtra 

automatiquement 

• Astuce: 

• Pensez à rajouter un raccourcit sur votre Bureau 

jeudi 26 janvier 12

ANDROID SDK 


• Bibliothèque spécifique à Android 

• Compilateur Dalvik (Machine Virtuelle Android) 

• Emulateur Android (Pour tester sans périphérique Android) 

• Environnement de débuggage DDMS 

• Documentation 

• Installation 

• http://developer.android.com/sdk/installing.html 

• Developer’s Guide 

• http://developer.android.com/guide/developing/index.html 

• JavaDoc (API Reference) 

• http://developer.android.com/reference/classes.html 

• Tutoriels & articles 

• http://developer.android.com/resources/index.html 


Bookmarkez ces URLs!

INSTALLATION DU SDK 

• Téléchargez et lancez l’installeur 

• A partir de http://developer.android.com/sdk/ 

• I’installez dans C:\android-sdk-windows 

• Sets up basic SDK, but omits many components 

• Instructions détaillées 

• http://developer.android.com/sdk/installing.html 

• A faire plus tard 

• Après l’installation du plugin eclipse, nous lancerons la mise à jour 

du SDK, pour obtenir les composants manquants. 

• Plus facile à faire à partir d’eclipse qu’à partir de la ligne de 

commande. 

jeudi 26 janvier 12


PLUGIN ADT 

• ADT (Android Development Tools) fournit plusieurs 

fonctionnalitées accessibles directement depuis eclipse : 

• Intégration entre Eclipse & les outils Android en lignes de 

commandes 

• Constructeur GUI en Drag-and-drop 

• Plusieurs ajouts pour le dev et debug. 

• Instructions détaillées: 


• http://developer.android.com/sdk/eclipse-adt.html

INSTALLATION DE ADT 

• Etapes : 

• Démarrez Eclipse 

• Help � Install New Software … 

• Clickez sur “Add” dans le coin en haut à 

droite 

• Dans «Add Repository», pour le champ 

nom entrez «ADT Plugin» et pour le 

champ adresse saisissez https://dlssl.google.com/android/eclipse/ 

• Clickez sur OK, sélectionnez la checkbox 

à coté de «Developer Tools», suivant, 

acceptez la licence et terminez. 

• Mettez à jour le plugin ADT 

• Help � Check for Updates 

jeudi 26 janvier 12

CONFIGURATION DE ADT 

• Définissez l’adresse du SDK 

• Window � Preferences � Android 

• Clickez Browse et indiquez l’endroit où vous avez installez le SDK 

• Optionnel: décochez envoyez les stats à Google 

• Window � Preferences � Android � Usage Stats 

jeudi 26 janvier 12

MISE À JOUR DES 

COMPOSANTS DU SDK 

• Lancez le SDK manager 

• Window � Android SDK & AVD Manager 

• Clickez sur “Available packages” à gauche 

• Sélectionnez toutes les entrées non-obsolète “Android 

Repository” entries 

• Sélectionnez la checkbox à côté de “Android 

Repository”, désélectionnez les entrées obsolètes, 

puis “Install Selected” 

• Prend un long moment pour s’exécuter 


• http://developer.android.com/ 

sdk/adding-components.html 

jeudi 26 janvier 12

ANDROID VIRTUAL DEVICES 

(AVDS) 


• Un AVD (Android Virtual Device) est une configuration d’Emulateur 

Android qui vous laisse modéliser votre périphérique en définissant le 

hardware et le software présents 

• Concept 

• Définissez plusieurs AVDs avec différentes API Android pour tester vos apps 

avec au moins : 

• Une version récente (ex: 3.x ou 2.3.3) 

• Une version courante (2.2 as ou 2011) 

• Les statistiques d’utilisations des périphériques Android sont disponible à 

http://developer.android.com/resources/dashboard/platform-versions.html 


• http://developer.android.com/guide/developing/devices/managing-avds.html 

jeudi 26 janvier 12

DÉFINITION D’UN AVD 

• Création 

• Window � Android SDK puis AVD Manager 

• Clickez sur “Virtual devices” à gauche. Clickez Ajout, choisissez options. Vous pouvez 

créer plusieurs AVDs.. 

• Options 

• Cible (ex: version de l’API) 

• 3.x 4.x pour tester les tablettes 

• 2.3.3 pour tester les téléphones ‘récent’ 

• 2.2 pour tester sur des générations plus anciennes 

• Taille de la SD Card 

• Pas indispensable de le renseigner (ou alors 4 Go) 

• Skin 

• Choisissez «default for the target you chose» 

jeudi 26 janvier 12

LANCEMENT D’UNE APPS SUR 


L’EMULATEUR

DANS LES GRANDES LIGNES 

• Lancement d’une apps 

• Bientôt, vous écrirez votre apps et la lancerez, mais pour le moment , on va utiliser 

une apps toutes faites. 

• Façons de lancer une apps: 

• Couverte maintenant 

• Emulateur Android : Déploiement direct à partir d’Eclipse. 

• Lors de développement, vous utilisez ce mode pour réaliser vos tests 

• Sur un périphérique Android : Déployé à partir d’un PC via le port USB. 

• Couverte plus tard dans cette sections 

• Sur un périphérique Android : Déployé à partir d’un site Web 

• Sur un périphérique Android : Déployé via les email. 

• Sur un périphérique Android : Déployé à partir de l’Android Market 

• Vos propres apps 

• Couvert plus tard, c’est la partie amusante ! 

jeudi 26 janvier 12

LANCEMENT DE HELLOANDROID 

DANS L’EMULATEUR 

• HelloAndroid 

• Apps très simple à déployer et à exécuter 

• Téléchargez le projet à partir de la section «Getting Started» du tutoriel Android et 

importez le dans Eclipse. 

• http://www.coreservlets.com/android-tutorial/ 

• Etapes 

• Import 

• File � General � Existing Projects… 

• Click-D sur ‘project’ à gauche 

• Run As � Android Application 

• Longue attente pour que l’émulateur s’initialise 

• Ne fermez pas l’émulateur lorsque vous avez finit ! 


• La prochaine fois, l’apps se chargera plus rapidement


HELLOANDROID 

Code will be discussed in next tutorial section.


HELLO ANDROID

CONCEPTS DE BASE 

• Concept 

• Lorsque vous créez une nouvelle apps, elle a un simple “Hello World” par défault 

• Vous pouvez donc créer une apps sans connaître la syntaxe 

(que nous verrons lors des prochaines séances) 

• Etapes 

• File � New � Project � Android � Android Project 

• La prochaine fois, vous pourrez faire 

File � New � Android Project 

• Remplissez les options comme indiqué 

• Lancez le projet comme précédemment 

• click-D � Run As � Android Application 

jeudi 26 janvier 12

DÉFINITION DES OPTIONS 

DU PROJETS 

• Paramétrage d’un nouveau projet Android 

• Project Name 

• Nom du projet sous eclipse, suivez votre propre convention. 

• Build Target 

• Version d’Android que vous souhaitez utiliser. Pour la plupart des téléphone, choisissez 2.2 ce qui est le plus 

utilisé dans le monde. 

• Application name 

• Nom de l’apps lisible par l’humain, le titre sera visible sur la barre Android. 

• Package name 

• L’application sur un device Android doit avoir un nom de paquet unique. Une façon de procéder est de 

faire : com.yourCompany.project 

• Create Activity 

• Le nom de la classe java la plus haute 

• Min SDK Version 

• Numéro qui doit correspondre au Build Target. 

Plus de détails à http://developer.android.com/guide/appendix/api-levels.html 

jeudi 26 janvier 12



DU PROJETS 

Eclipse project name 

Android version that you want to run on 

Human-readable app name 

Package. Use naming convention to ensure uniqueness 

Java class name 

Number corresponding to build target

LANCEMENT DE VOTRE APPS 

• Fonctionnalitées embarquées 

• Tout nouveau projet a automatiquement un comportement de type “Hello World” 

• Etape d’execution 

• click-D � Run As � 

Android Applicaton 

• Rappel : Ne fermez pas l’émulateur 

après vos tests. 

jeudi 26 janvier 12


VISUALISATION DES SORTIES 

STANDARDS AVEC DDMS

LES BASES DE DDMS 

• Concepts 

• DDMS (Dalvik Debug Monitor Service) est un outils qui réalise plusieurs choses 

• Simule un appel entrant sur l’émulateur 

• Peut définir une position GPS dans l’émulateur 

• Voir les print et les erreurs de runtime 

• Définir la position & prendre des screenshots 

de votre device Android 

• Utilisation simple 

• Démarrez DDMS 

• Window � 

Open Perspective � DDMS 

• Une fois cette opération faite, 

vous pourrez clicker sur “DDMS” en haut 

à droite d’eclipse 

• Clickez sur “Java” poure revenir au code 

• Visualisation des print 

• Observez dans la fenêtre ‘LogCat’ en bas 

• Type part of output into Filter field to see specific output 

jeudi 26 janvier 12

SORTIE DDMS 

(HELLOANDROID) 

• Code 

• Ajoutez un System.out.println 

Dans le main de la méthode 

onCreate 

• Observez le code dans la copie 

d’écran de la page précédente 

• La méthode onCreate et le reste 

sera abordé plus tard 


Output of System.out.println 

Entered so it is easier to find specific output among 

the many informational messages that emulator prints

LANCEMENT D’UNE APPS SUR 


UN PÉRIPHÉRIQUE ANDROID

LANCEMENT 

• Concept 

• La plupart des tests que vous ferez seront réalisé dans l’émulateur Android. Parfois vous 

aurez besoin, de faire des tests sur un VRAI device pour tester la compatibilité, la caméra 

(Réalité augmenté), le GPS, la liste des contacts, ... 

• Vous devez premièrement réaliser un package d’application signé (YourApp.apk). Ensuite, il y a plusieurs 

option pour l’envoyer sur le périphérique 

• Options 

• Couverte maintenant 

• Connexion USB, et adb pour la déployer 

• Couverte plus tard 

• Soumettre une application à l’Android Market 

• En autoformation ;) 

• Par l’envoie d’une apk par un email lu sur le téléphone 

• Déploiement de l’apps (fichier apk) sur un site web, et connexion sur ce site pour télécharger le fichier. 

( Il faut définir le type MIME à application/vnd.android.package-archive ) 

jeudi 26 janvier 12

VIA L’USB 

• Prérequis : il faut installer les drivers pour le périphérique Android correspondant. 

• Brancher le device 

• Les OS récents devraient trouver le driver automatiquement, sinon le télécharger à 

partir du site du constructeur : 

http://developer.android.com/sdk/oem-usb.html 

• Etapes 

• Sur le device Android 

• Dans préférence, passez en mode debug USB 

• Autorisez les sources inconnues 

• Eclipse 

• Exportez un package d’application signé (YourApp.apk) 

• adb 

• Allez dans sdk-install-dir\tools (où mettez ce chemin dans le PATH) 

• Lancez “adb install YourApp.apk” 

jeudi 26 janvier 12

CONFIGURATION DU DEVICE 

• Passer en mode debug USB 

• Settings � Applications � 

Development 

• Nécessaire : USB debugging 

• permet au PC de se connecter en USB 

• Optionel: Stay awake 

• Le device ne passera pas en mode eco 

• Optionel: Allow mock locations 

• Autorise le PC à envoyer de faux 

signaux GPS 

• Autoriser les sources inconnues 


Unknown sources 

jeudi 26 janvier 12

EXPORTER UN PACKAGE 

• A faire à chaque fois : Export 

• click-D Eclipse project 

• Android Tools � Export 

Signed Application Package 

• Uniquement la première: définition d’une clé 

• Il vous sera demandé de donner l’adresse 

d’un fournisseur de clé et un mot de 

passe. La clé sera crée et l’apps signée, ce 

qui est un format valide mais elle ne sera 

pas certifié par un organisme de 

confiance. 

jeudi 26 janvier 12

INSTALLATION AVEC ADB 

• Connectez le device en USB 

• Ouvrez une fenêtre de commande 

• Windows Start Menu � Run � cmd 

• Allez dans le répertoire du SDK “platform-tools” 

• ..\android-sdk\platform-tools 

• Exécutez “adb install YourApp.apk” 

• > adb install HelloAndroid.apk 

1439 KB/s (13262 bytes in 0.009s) 

pkg: /data/local/tmp/HelloAndroid.apk 

Success 

jeudi 26 janvier 12


LANCEMENT DE L’APP 

• Allez dans applications ou installed 

apps 

• Tapez new app 

• Rappelez vous du nom humain 

donné à votre appli lors de sa 

création (Application Name) 

c’est celui qui apparait ici. 

• Pour mettre à jour le programme 

• Désinstallez au préalable la 

précédente version 

• Settings � Applications 

� YourApp � Uninstall


CONCLUSION

RÉSUMÉ 

• Installation des logiciels (venez avec vos PC la prochaine fois si vous voulez) 

• Java 6, Eclipse, Android SDK, Eclipse ADT plugin 

• Mise à jour de vos Bookmarks pour la doc 

• Developer’s Guide et + à developer.android.com 

• Mise à jour et configuration des logiciels 

• Adresse du SDK dans Eclipse 

• Mise à jour des composants via le SDK & AVD Manager 

• Définition d’au moins une AVD pour lancer vos apps sur un émulateur 

• Lancement d’une apps 

• Sur l’émulateur (la plupart du tps). click-D project, Run As � Android Application. 

• Sur le device (de tps en tps). construction d’un apk signé et utilisation d’adb. 

• Réalisation d’une nouvelle app 


• Visualisation de la sortie d’écran de print 

• Dans la fenêtre LogCat de DDMS 

jeudi 26 janvier 12


QUESTIONS?

CONCEPTS DE BASE DE LA 

PROGRAMMATION ANDROID 







• Réaliser & tester un projet Android 

• Structure de base d’un programme 

• Layout Java 

• Layout XML 

• Eclipse ADT visual layout editor 

• Layout Hybrid 

• Résumé de la structure d’un Project 

jeudi 26 janvier 12


RÉALISER UN PROJET 

ANDROID

PETIT RAPPEL 

• Déjà installé 

• Java 6 

• Eclipse 

• Android SDK 

• Eclipse ADT Plugin 

• Déjà configuré 

• Les composants SDK d’Android sont à jour 

• Eclipse préférences 

• Adresse du SDK Android définie 

• Au moins 1 AVD (Android Virtual Device) définit 

• Documentation 

• http://developer.android.com/guide/developing/index.html 

• http://developer.android.com/reference/packages.html 

jeudi 26 janvier 12

RÉALISER VOTRE PROPRE 

PROJET ANDROID: LES BASES 

• Concepts 

• Lors de la création d’une nouvelle apps, elle dispose déjà des fonctionnalités du 

‘HelloWorld’. 

• So, you can create and test an app without knowing syntax (which is not 

discussed until next tutorial section) 

• Steps 


• Once you do this once, next time you 

can do File � New � Android Project 

• Fill in options as shown on next page 

• Run new project as shown previously 

• R-click � Run As � 

Android Application 

jeudi 26 janvier 12


DU PROJETS 

• Paramétrage d’un nouveau projet Android 

• Project Name 

• Nom du projet sous eclipse, suivez votre propre convention. 

• Build Target 

• Version d’Android que vous souhaitez utiliser. Pour la plupart des téléphone, choisissez 2.2 ce qui est le plus 

utilisé dans le monde. 

• Application name 

• Nom de l’apps lisible par l’humain, le titre sera visible sur la barre Android. 

• Package name 

• L’application sur un device Android doit avoir un nom de paquet unique. Une façon de procéder est de 

faire : com.yourCompany.project 

• Create Activity 

• Le nom de la classe java la plus haute 

• Min SDK Version 

• Numéro qui doit correspondre au Build Target. 

Plus de détails à http://developer.android.com/guide/appendix/api-levels.html 

jeudi 26 janvier 12



DU PROJETS 

Eclipse project name 

Android version that you want to run on 

Human-readable app name 

Package. Use naming convention to ensure uniqueness 

Java class name 

Number corresponding to build target

LANCEMENT DE VOTRE APPS 

• Fonctionnalitées embarquées 

• Tout nouveau projet a automatiquement un comportement de type “Hello World” 

• Etape d’execution 

• click-D � Run As � 

Android Applicaton 

• Rappel : Ne fermez pas l’émulateur 

après vos tests. 

jeudi 26 janvier 12

LANCER UNE NOUVELLE APP 

SUR UN DEVICE ANDROID 

• Apps non signée : trivial 

• Brancher le téléphone et la lancer à partir d’Eclipse 

• Etapes 


• Configurer le téléphone pour accepter des apps non vérifiées 

• Arrêter l’émulateur 

• Brancher le dévice 

• Click-D «project» 

• Run As � Android Application 

• Cela installe et lance l’apps. L’apps est laissée sur le device 

même une fois celui-ci débranché.

CONFIGURATION DU DEVICE 

• Passer en mode debug USB 


Development 

• Nécessaire : USB debugging 

• permet au PC de se connecter en USB 

• Optionel: Stay awake 

• Le device ne passera pas en mode eco 

• Optionel: Allow mock locations 

• Autorise le PC à envoyer de faux 

signaux GPS 

• Autoriser les sources inconnues 


Unknown sources 

jeudi 26 janvier 12


STRUCTURE D’UN 

PROGRAMME

STRUCTURE GÉNÉRALE 

(COMMUNE À TOUTES LES 

package com.companyname.projectname; 

import android.app.Activity; 

import android.os.Bundle; 

import android.widget.SomeLayoutOrView; 

APPROCHES) 

There is no need to type the import statements by hand. Just use the classes in your code, and when 

Eclipse marks the line as an error, click on the light bulb at the left, or hit Control-1, then choose to have 

Eclipse insert the import statements for you. 

public class SomeName extends Activity { 

@Override 

public void onCreate(Bundle savedInstanceState) { 

super.onCreate(savedInstanceState); 

SomeLayoutOrView view = createOrGetView(); 

... 

setContentView(view); 

} 

... 

} 


Apps are frequently shut down by the device. This lets 

you remember some info about the previous invocation. 

Covered in later lectures, but for now, just know that you 

should always call super.onCreate as first line of 

onCreate. 

I also follow a few official Android coding conventions here (4-space indentation, no *’s in imports, {’s on same line as previous code, @Override where appropriate). Conventions 

are strictly enforced in official code, and are used in all examples and tutorials. So, you might as well follow the conventions from the beginning. Follow these simple ones for 

now, and a later lecture will give coding convention details and provide an Eclipse preferences file to help with them.

LES 3 APPROCHES 

PRINCIPALES 

• Java 

• Définition directement en Java des Strings Strings, window layout window, création des boîtes 

de contrôle, et assignation des event handlers. (~ Programmation swing) 

• XML 

• Définition à l’aide de fichiers XML les Strings, window layout, création des boîtes de 

contrôle, et assignation des event handlers. Les méthodes Java liront le layout à partir du 

fichier XML et le à setContentView. 

• Hybride 

• Utilisation des fichiers XML pour la définition des Strings, window layout et la création des 

boîtes de contrôle. Utilisation de Java pour l’assignation des event handlers. 

• Exemples dans ce tutoriel 

• Le bouton qui dit “Show Greeting”. Un petit message popup apparaîtra lorsque le bouton 

sera pressé. 

• Implémenté selon les 3 façons. 

jeudi 26 janvier 12


APPROCHE JAVA: SCHÉMA 

public class SomeName extends Activity { 




String message = "..."; 

LinearLayout window = new LinearLayout(this); 

window.setVariousAttributes(…); 

Button b = new Button(this); 

b.setText("Button Label"); 

b.setOnClickListener(new SomeHandler()); 

mainWindow.addView(b); 

... 

setContentView(window); 

} 

private class SomeHandler implements OnClickListener { 


public void onClick(View clickedButton) { 

doSomething(...); 

} 

} } 

OnClickListener is a public inner class inside View. But, as long as you import android.view.View.OnClickListener, you use it just 

like a normal class. And, remember that Eclipse helps you with imports: just type in the class name, then either click on the light 

bulb or hit Control-1 to have Eclipse insert the proper import statements for you.

APPROCHE XML: SCHÉMA 

• Java 

public class SomeClass extends Activity { 




setContentView(R.layout.main); 

} 

public void handlerMethod(View clickedButton) { 

String someName = getString(R.string.some_name); 

doSomethingWith(someName); 

} } 

• XML 


res/values/strings.xml res/layout/main.xml 

 

 

… 

… 

 

 

 

 

 

APPROCHE HYBRIDE: SCHÉMA 

• Java 

public class SomeClass extends Activity { 





Button b = (Button)findViewById(R.id.button_id); 

b.setOnClickListener(new SomeHandler()); 

} 

private class SomeHandler implements OnClickListener { 



doSomething(...); 

} 

} } 

• XML 

• On donne un ID aux controls qui ont besoin d’un handlers 

• NE PAS utiliser android:onClick pour attribuer un handler 

jeudi 26 janvier 12


LAYOUT JAVA

CONCEPTS 

• Approche 

• Définition directement en Java des Strings Strings, window layout window, 

création des boîtes de contrôle, et assignation des event handlers. (~ 

Programmation swing) 

• Avantages 

• Proche des méthodes de dev sur dektop. (~ Swing, SWT & AWT). 

• Bien pour les layouts dynamique (ex: qui change en fonction fonction du 

programme). 

• Inconvénients 

• Difficile à maintenir (~discutable, mais il y a consensus) 

• Fonctionnement chaotique avec I18N 

• Pas recommandé sauf pour les layouts dynamiques 

• Acceptable pour l’App Store sous réserve d’un bon fonctionnement (il n’y a 

pas de police qui traque les mauvais élèves/codeurs). 

jeudi 26 janvier 12


CODE (CORPS) 

public class SayHelloJava extends Activity { 




String appName = "SayHello Application"; 

String windowText = 

"Press the button below to receive " + 

"a friendly greeting from Android."; 

String buttonLabel = "Show Greeting"; 

LinearLayout mainWindow = new LinearLayout(this); 

mainWindow.setOrientation(LinearLayout.VERTICAL); 

setTitle(appName); 

TextView label = new TextView(this); 

label.setText(windowText); 

mainWindow.addView(label); 

Button greetingButton = new Button(this); 

greetingButton.setText(buttonLabel); 

greetingButton.setOnClickListener(new Toaster()); 

mainWindow.addView(greetingButton); 

setContentView(mainWindow); 

}

} 


CODE (EVENT HANDLER) 

private class Toaster implements OnClickListener { 



String greetingText = "Hello from Android!"; 

Toast tempMessage = 

Toast.makeText(SayHelloJava.this, 

greetingText, 

Toast.LENGTH_SHORT); 

tempMessage.show(); 

}

RÉSULTAT SUR L’ ÉMULATEUR 

• click-D, Run As � Android Application 

jeudi 26 janvier 12

RÉSULTATS SUR UN DEVICE 

• Configurez le device 

• Arrêter l’émulateur, branchez le device 

• Click-D project, Run As � Android Application 

jeudi 26 janvier 12


LAYOUT XML

CONCETS 

• Approche 

• Définition à l’aide de fichiers XML les Strings, window layout, création des boîtes de 

contrôle, et assignation des event handlers. 

• Définition des layout et contrôles dans res/layout/main.xml 

• Définition des Strings dans res/values/strings.xml 

• Avantages 

• Plus facile à maintenir 

• Bonne compatibilité avec I18N 

• Possibilité d’utiliser l’éditeur Visuel d’Eclipse 

• Approche Standard/recommndée 

(avec l’approche hybride) 


• Ne fonctionne pas avec les layouts dynamiques 

jeudi 26 janvier 12

PLUS DE DÉTAILS 

• res/layout/main.xml 

• Définit le layout et le controls à l’aide d’une description XML 

• Define controls 

• Fait référence aux strings (de strings.xml) avec @string/string_name 

• Assigne un event handler avec android:onClick 

• res/values/strings.xml 

• Définit les strings utilisées dans le GUI ou qui peuvent changer avec I18N 

res/layout/main.xml 

• Code Java 

• Fait référence aux layout avec R.layout.main 

• Fait référence aux strings avec getString(R.string.string_name) 

• Fait référence aux controls avec findViewById(R.id.some_id) 

• Plus d’info 

• http://developer.android.com/guide/topics/ui/declaring-layout.html 

jeudi 26 janvier 12


LAYOUT DU PROJET 

Refers to layout defined in res/layout/main.xml with 

R.layout.main. 

Refers to strings defined in res/values/strings.xml with 

getString(R.string.string_name) 

Defines screen layout and GUI controls. Optionally assigns event 

handlers to controls. 

Refers to strings defined in res/values/strings.xml with @string/ 

string_name 

Conventional for main file to be called main.xml, but not required. If it is 

foo.xml, then Java uses R.layout.foo. As we will see later, complex apps 

have several layout files for different screens. 

Defines strings that are either used in GUI controls or that might 

change with internationalization.

RES/LAYOUT/MAIN.XML 

 

 

 

 

 


These attributes (android:orientation, etd.) 

are defined in JavaDoc API for 

LinearLayout. 

These strings are defined in res/values/ 

strings.xml 

This must be a public method in main class, have a void 

return type, and take a View as argument. No interface 

needs to be implemented, as it does with event handlers 

referred to in Java code.

RES/VALUES/STRINGS.XML 

 

 

Say Hello Application 

 

Press the button below to receive 

a friendly greeting from Android. 

 

Show Greeting 

Hello from Android! 

 


app_name is special, predefined name (although it can be 

overridden in AndroidManifest.xml) 

All the rest are developer-specified names. 

main.xml refers to this with @string/greeting_text 

Java refers to this with getString(R.string.greeting_text) 

Eclipse auto-completion will recognize the names when editing other 

files that use them.

} 


CODE (JAVA) 

public class SayHelloXml extends Activity { 





} 

public void showToast(View clickedButton) { 

String greetingText = getString(R.string.greeting_text); 


Toast.makeText(this, greetingText, 



}

• Dans l’émulateur 

• Click-D project, Run As � 


RÉSULTATS 

• Apparence & comportement identique à l’exemple tout Java 

• Sur le device 

• Configurez le téléphone 

• Arrêtez l’émulateur et branchez le device 



• Apparence & comportement identique à l’exemple tout Java


ECLIPSE ADT 

VISUAL LAYOUT EDITOR

ECLIPSE VISUAL GUI BUILDER & 

EDITOR 

• Invocation 

• Lors de l’édition du main.xml, clickez sur Graphical Layout 

• Fonctionnalités 

• Peut changez interactivement les attributs du layout (vertical/horizontal, caractéristiques, etc.) 

• Peut faire du drag&drop à partir de la palette de contrôle GUI disponible 

• Peut définir interactivement les caractéristiques de contrôle (couleurs, remplissage, event 

handler, etc.) 

• Prévisualisation 

• Attention 

• Bien que l’éditeur visuel est très pratique, cela ne vous dispense pas de l’édition manuelle des 

fichiers XML, pour définir l’indentation, l’ordre des attributs .... 

• Plus d’info 

• http://tools.android.com/recent 

• http://www.youtube.com/watch?v=Oq05KqjXTvs 

jeudi 26 janvier 12


ECLIPSE VISUAL LAYOUT 

EDITOR


HYBRID LAYOUT

• Approches 

CONCEPTS 

• Utilisation des fichiers XML pour la définition des Strings, 

window layout et la création des boîtes de contrôle. 

• Utilisation de Java pour l’assignation des event handlers. 

• Avantages 

• Les mêmes que pour l’approche XML 

• Mais, puisque les event handler ont besoin d’être édité en Java, il 

y a plus de sens de les assignés en aussi en Java. 



• Ne fonctionne pas avec les layouts dynamiques


 

 

 

 

 


We define an id for the button, so that the 

button can be referred to in Java code with 

findViewById(R.id.greeting_button) 

We do not assign an event handler to the button, as 

we did in the previous example.


 

 

Say Hello Application 

 

Press the button below to receive 

a friendly greeting from Android. 

 

Show Greeting 

Hello from Android! 

 


No changes from previous example.


CODE (JAVA) 

public class SayHelloHybrid extends Activity { 





Button greetingButton = 

(Button)findViewById(R.id.greeting_button); 

greetingButton.setOnClickListener(new Toaster()); 

} 

private class Toaster implements OnClickListener { 



String greetingText = getString(R.string.greeting_text); 


Toast.makeText(SayHelloHybrid.this, 

greetingText, 



} 

}} 

You must call setContentView before 

calling findViewById. If you call 

findViewById first, you get null.

• Dans l’émulateur 

• Click-D project, Run As � 


RÉSULTATS 

• Apparence & comportement identique à l’exemple tout Java 

• Sur le device 

• Configurez le téléphone 

• Arrêtez l’émulateur et branchez le device 



• Apparence & comportement identique à l’exemple tout Java


CONCLUSION


PROJECT LAYOUT 

Refers to layout defined in res/layout/main.xml with 

R.layout.main. 

Refers to controls defined in res/layout/main.xml with 

findViewById(R.id.some_id) 

Refers to strings defined in res/values/strings.xml with 

getString(R.string.string_name) 

Defines screen layout and GUI controls. Optionally assigns event 

handlers to controls. 

Refers to strings defined in res/values/strings.xml with @string/ 

string_name 

Defines strings that are either used in GUI controls or that might 

change with internationalization.

RÉSUMÉ 

• XML 


• Définit les propriétés du layout et le contrôle du GUI. 

• Parfois assigne des event handlers à du contrôle 


• Définit les Strings utilisés dans le GUI ou pour le I18N. 

• Java 

• La classe principale étend la classe Action 




maybeFindControlAndAssignHandler(…); 

} 

• Le Event handler prend un View en argument 

• Si il est assigné en Java, il faut implémenter 

OnClickListener (ou un autre Listener) 


Call setContentView 

before calling 

findViewById. 

Widget event handling is 

covered in detail in next 

tutorial section.


QUESTIONS?


WIDGET EVENT HANDLING 






• Utilisation d’une classe Listener séparée 

• Utilisation d’une inner classe nommée 

• Utilisation d’une inner classe anonyme 

• Utilisation de l’ Activity 

• et implémentation de l’interface Listener 

• Utilisation de l’ Activity 

• et spécification des méthodes dans le fichier layout 

(main.xml) 

• Copie et rennomage de projet Android sous Eclipse 

jeudi 26 janvier 12


UTILISATION D’UNE CLASSE 

LISTENER SÉPARÉE

CONCEPTS 

• Buts 

• Changer la couleurs d’un TextView lorsqu’un Button ou RadioButton est pressé. 

Gestion de différentes couleurs en fonction du bouton. 

• Approches 

• Utilisation d’une classe externe qui implémente View.OnClickListener 

• Import android.view.View.OnClickListener, et dit alors “implements OnClickListener” 

• Avantages 

• Il est possible de donner des arguments pour changer le comportement 

• La séparation des classes généralement ne promouvoit qu’un couplage faible 

• Si le gestionnaire d’événement peut s’appliquer à différents contrôles, il peut être changé 

indépendamment du reste de l’application.. 


• Si vous voulez appeler du code à partir du main Activity, vous aurez besoin de 

références 

• En plus le code dans le main Activity doit être public 

jeudi 26 janvier 12


RÉSUMÉ SUR LE LAYOUT 

Button 

Button 

Button 

Horizontal 

RadioGroup 

(Containing 3 RadioButtons) 

TextView 

(No text, but controls will 

change the background 

color of this region.) 

Vertical 

LinearLayout 

An upcoming tutorial section gives details on using layouts. However, you can 

do a pretty lot now by knowing just two simple things: 

1) You can make some pretty complex layouts by nesting horizontal and 

vertical layouts inside each other. 

2) You can experiment interactively with the visual layout editor in Eclipse. 

Edit main.xml and click on Graphical Layout.


 

 

 

 

 


Overall layout is a vertical stack of graphical items. 

This part defines the 3 buttons shown on the previous slide. 

Each button is given an id so that it can be found in Java via 

findViewById, then assigned an event handler via 

setOnClickListener. 

The text (Button label) is taken from strings.xml instead of 

entered directly here, because the same label will also be used 

for RadioButtons.



 

 

 

 

 

A horizontal RadioGroup gives the same layout as a 

horizontal LinearLayout, except that it contains only 

RadioButtons. A RadioGroup also means that only 

one of the RadioButtons inside can be selected at 

any given time.


 

 


This defines the blank region at the bottom that will 

change colors when the Buttons or RadioButtons 

are clicked. I used a TextView because I might later 

want to put some text inside.


 

 

Event Handling Example 

Red 

Blue 

Yellow 

 


main.xml refers to these names with @string/red_prompt, @string/ 

blue_prompt, and @string/yellow_prompt. 

Each string is used as label for one Button and one RadioButton.


MAIN ACTIVITY CLASS 

public class Events1Example extends Activity { 

private View mColorRegion; 





mColorRegion = findViewById(R.id.color_region); 

Button b1 = (Button)findViewById(R.id.button1); 



RadioButton r1 = 

(RadioButton)findViewById(R.id.radio_button1); 





This part just looks up the controls 

that were defined in main.xml, and 

assigns them to variables. Note the 

Android coding convention that nonpublic 

instance variables (data 

members) start “m”.

} 

} 



(CONTINUED) 

b1.setOnClickListener(new ColorSetter(Color.RED, this)); 

b2.setOnClickListener(new ColorSetter(Color.BLUE, this)); 

b3.setOnClickListener(new ColorSetter(Color.YELLOW, this)); 

r1.setOnClickListener(new ColorSetter(Color.RED, this)); 

r2.setOnClickListener(new ColorSetter(Color.BLUE, this)); 

r3.setOnClickListener(new ColorSetter(Color.YELLOW, this)); 

public void setRegionColor(int color) { 

mColorRegion.setBackgroundColor(color); 

} 

Since this method will be called 

by method in separate event 

handler class, it must be public. 

Assigns a separate class as the event handler for 

each of the Buttons and RadioButtons. 

Good news: you can pass arguments to the event 

handler (the colors) so that the same event 

handler class can have different behaviors for 

different controls. 

Bad news: you have to pass a reference to the 

main Activity (“this” above) so that the event 

handler can call back to code in the Activity.

} 


EVENT HANDLER CLASS 

public class ColorSetter implements OnClickListener { 

private int regionColor; 

private Events1Example mainActivity; 

public ColorSetter(int regionColor, 

Events1Example mainActivity) { 

this.regionColor = regionColor; 

this.mainActivity = mainActivity; 

} 


public void onClick(View v) { 

mainActivity.setRegionColor(regionColor); 

} 

Event handler must store a reference to the main Activity so that it can call back to it. 

Another option in this particular case would be to pass the TextView to the event 

handler, but passing the main Activity is a more general solution.


RÉSULTATS DANS L’ 

EMULATEUR


RÉSULTATS SUR UN DEVICE


UTILISATION D’UNE INNER 

CLASSE NOMMÉE

IDÉE 

• Buts 

• Changer la couleurs d’un TextView lorsqu’un Button ou RadioButton est 

pressé. Gestion de différentes couleurs en fonction du bouton. 

• Idem précédent 

• Approche 

• Utilisation d’une inner classe qui implémente View.OnClickListener 

• Avantages 

• Il est possible de donner des arguments pour changer le comportement 

• La méthode du gestionnaire d’événement peut accéder aux données 

privées de l’Activity. Pas besoin de référence pour appeler l’Activity. 


• La classe Listener est dans le même fichier que l’activity, elles sont plus 

liées et ne peuvent pas être changées indépendamment l’une de l’autre. 

jeudi 26 janvier 12

XML FILES: IDEM PRÉCÉDENT 


• Définit un LinearLayout vertical qui contient 3 Buttons, un 

RadioGroup horizontal (avec 3 RadioButtons), et un 

TextView. 

• Les Buttons, RadioButtons, et TextView ont le même 

identifiant auxquels ont peut faire référence dans le code 

Java 



• Définit le nom de l’application et les labels des Buttons et 

RadioButtons



















Except for the class name, this top 

part of the Activity is exactly the same 

as the previous example.

} 



b1.setOnClickListener(new ColorSetter(Color.RED, this)); 

b2.setOnClickListener(new ColorSetter(Color.BLUE, this)); 

b3.setOnClickListener(new ColorSetter(Color.YELLOW, this)); 

r1.setOnClickListener(new ColorSetter(Color.RED, this)); 

r2.setOnClickListener(new ColorSetter(Color.BLUE, this)); 

r3.setOnClickListener(new ColorSetter(Color.YELLOW, this)); 

private void setRegionColor(int color) { 


} 

Since this method will only be called 

by method in inner event handler 

class, it is allowed to be private. 

Note no closing brace. This class is not 

finished yet (continued on next slide) 

Assigns an inner class as the event handler for each 

of the Buttons and RadioButtons. 

As with the previous example, you can pass 

arguments to the event handler (the colors) so that 

the same event handler class can have different 

behaviors for different controls. 

However, since the event handler is in the same 

class, you do not have to supply a reference to the 

main Activity class.

EVENT HANDLER CLASS 

(PARTIE DE MAIN ACTIVITY CLASS) 

} 

} 


private class ColorSetter implements OnClickListener { 

private int regionColor; 

public ColorSetter(int regionColor) { 

this.regionColor = regionColor; 

} 



setRegionColor(regionColor); 

} 

Closes off the main Activity class. 

Event handler can directly call methods in the main Activity, 

even if the method is private.

RÉSULTATS SUR L’ EMULATEUR 


Same as previous example.


RÉSULTAT SUR UN DEVICE 



UTILISATION D’UNE INNER 

CLASSE ANONYME POUR LA 

GESTION DES ÉVÉNEMENTS

CONCEPT 

• Buts 

• Changer la couleur aléatoirement du TextView lorsque le Button est préssé. 

• Approche 

• Utilisation d’une inner class anonyme qui implémente le Listener 

• Avantages 

• Si l’on part du principe que l’on a une classe par contrôle, on a les mêmes 

avantages qu’une inner classe nommée, mais en plus concis. 

• Approche que l’on retrouve dans Swing, SWT, AWT, and GWT. 


• Si l’on applique le handler à plus d’un control, il faudra faire du copié/collé du code 

que handler. 

• Ce type d’approche doit s’appliquer seulement pour un contrôle unique 

• Si le code pour les handler est long, cela rend le code plus difficile à lire en l’inlinant. 

• Approche utilisée seulement lorsque le code du handler est court 

jeudi 26 janvier 12


 

 

 

 

 

jeudi 26 janvier 12


 

 


Random Color 

 

jeudi 26 janvier 12


ACTIVITY CLASS 1: 

INNER CLASS NOMMÉE 



private int[] mColorChoices = 

{ Color.BLACK, Color.BLUE, ...}; 






Button colorButton = 

(Button)findViewById(R.id.color_button); 

colorButton.setOnClickListener(new ColorRandomizer()); 

} 



} 

There is nothing wrong with this approach. 

However, this event handler class is only 

used on this line of code. Furthermore, the 

code for ColorRandomizer (next page) is 

relatively short. So, you can make it a bit 

more concise with an anonymous inner class.

} 

} 



INNER CLASS NOMMÉE 

private class ColorRandomizer 

implements OnClickListener { 



Random generator = new Random(); 

int index = generator.nextInt(mColorChoices.length); 

setRegionColor(mColorChoices[index]); 

}



INNER CLASS ANONYME 




{ Color.BLACK, Color.BLUE, ...}; 



} 

See next page for onCreate



INNER CLASS ANONYME 








colorButton.setOnClickListener(new OnClickListener() { 






} 

}); 

} This defines the class and instantiates it all in one fell swoop. If you have never seen anonymous inner 

classes before, the confusion is probably not worth the code savings over a named inner class. 

However, once you are used to it, it is more concise and arguably easier to understand because the 

behavior is shown where it is used. This approach is very commonly used by Swing, SWT, AWT, and 

GWT programmers. This is also very analogous to anonymous functions (closures) that are widely 

used in functional programming languages.

RÉSULTATS SUR L’EMULATEUR 

jeudi 26 janvier 12


RÉSULTATS SUR UN DEVICE


GESTION DES ÉVÉNEMENTS AVEC 

L’ ACTIVITY QUI IMPLÉMENTE 

L’INTERFACE LISTENER

CONCEPT 

• Buts 

• Changer la couleur aléatoirement du TextView lorsque le Button est pressé 

• Approche 

• Avoir l’ Activity qui implémente l’interface Listener. Placer la méthode handler dans l’ Activity. 

Appeler setOnClickListener(this). 

• Avantages 

• Si l’app a un seul contrôle sur ce type de Listener, alors c’est la façon la plus simple et la plus 

rapide de toutes les approches. 


• Ne passe pas à l’échelle avec des contrôles multiples sauf si l’on a des comportements identiques. 

• Si l’on assigne “this” comme handler pour plus d’un contrôle du même type Listener, alors la méthode onClick (ou 

autre) deviendra complexe pour déterminer quel contrôle a été clické 

• Cette méthode est a réserver pour des apps qui ont un seul contrôle de ce type de Listener 

• Il n’est pas possible de passer des arguments au Listener 

• Donc, fonctionne difficilement pour des contrôles multiples 

jeudi 26 janvier 12


XML FILES: 

IDENTIQUE 

• Définit un LinearLayout vertical contenant un Button et un 

TextView. 

• Le Button et le TextView ont des ids qui pourront être 

utilisés pour y faire référence dans le code Java 



• Définit le nom de l’application et le label du Button



public class Events5Example extends Activity 

implements OnClickListener { 



{ Color.BLACK, Color.BLUE, ... }; 








colorButton.setOnClickListener(this); 

}

} 

} 










}


RÉSULTAT SUR L’ÉMULATEUR 



RÉSULTAT SUR LE DEVICE 

Same as 

previous 

example.


GESTION DES ÉVÉNEMENTS 

EN INDIQUANT LA 

MÉTHODE DANS LE 

MAIN.XML

CONCEPTS 

• Buts 

• Changer la couleur aléatoirement du TextView lorsque le Button est pressé. 

• Approche 

• Placer la méthode dans l’ Activity. Ne pas implémenter d’interface Listener ou appeler 

setOnClickListener. Avoir un fichier layout (main.xml) qui spécifie la méthode handler via 

l’attribut android:onClick 

• Avantages 

• Part du principe que l’app a un seul contrôle de ce Listener type. Avantages (code simple/court) 

identique à l’approche précédente. 

• Plus consistant avec la stratégie “do layout in XML” 

• Il est possible de fournir plusieurs nom de méthodes pour différents contrôles. 


• Il n’est toujours pas possible de passer des arguments au Listener. 

• Moins clair pour le développeur Java pour qui la méthode est le handler du contrôle 

jeudi 26 janvier 12


 

 

 

 

 


This is the name of the event handler 

method in the main class. This method 

must have a void return type and take a 

View as an argument. However, the 

method name is arbitrary, and the main 

class need not implement any particular 

interface.


 

 


Random Color 

 


Unchanged from the previous two examples






{ Color.BLACK, Color.BLUE, ... }; 






// No need to look up the button or assign event handler 

}

} 

} 





public void randomizeColor(View v) { 




} 

Matches method name given for 

android:onClick in main.xml


RÉSULTAT SUR L’ÉMULATEUR 



RÉSULTAT SUR LE DEVICE 

Same as 

previous 

example.


COPIE D’UN PROJET 

ANDROID SOUS ECLIPSE

ETAPES 

• Problème 

• Les projets dans ce tutoriel sont très proches les uns des autres. 

• Vous voulez copié/renomé vos précédents projets au lieu de créer de nouveau projet et de 

copié chaque partie de façon séparée 

• Mais, le noms des paquets sur le device doit être unique 

• Le renommage des paquets nécessite quelques précautions. Pas de vraie support dans Eclipse. 

• Etapes (l’ordre est important !) 

1. click-D sur le vieux projet. click-D et choississez Paste. New name. 

2. click-D nouveau projet, Android Tools � Rename Application Package. New 

name. Déselectionnez la classes Java, et laissez la sélection seulement pour le 

manifest. OK lorsque l’on vous demande de mettre à jour la configuration. 

3. click-D src/projectName dans le nouveau projet. Refactor � Rename. OK 

lorsque l’on informe que le paquet existe. 

4. Optionnel : click-D dans l’Activity. Refactor � Rename. 

jeudi 26 janvier 12


CONCLUSION

APPROCHES: CONTRÔLES 

SIMPLES OU MULTIPLES 

• Situation 

• Le même code de gestionnaire doit être appliqué à plusieurs contrôles 

• Options 

• Utiliser une classe gestionnaire d’événement séparée 

• Pros: possibilité de passer des args au gestionnaire afin de customiser son 

comportement; plus facile à changer indépendamment de l’app principale 

• Cons: Si le gestionnaire appel du code de l’ Activity, il faut utiliser “this” et rendre la 

méthode public 

• Utiliser une inner classe nommée 

• Pros: possibilité de passer des arps au gestionnaire afin de customiser son 

comportement; pas besoins de “this” reference, la méthode peut être privée 

• C’est de mon point de vue la méthode la plus facile pour la gestion des événement 

de type Widget 

• Cons: le gestionnaire est lié à l’Activity 

jeudi 26 janvier 12

APPROCHES: CONTRÔLE 

SIMPLE 

• Situation 

• Le code du gestionnaire doit être appliqué à un seul contrôle 

• Options 

• Utilisation d’une inner classe anonyme 

• Pros: identique à l’inner class nommée, et plus concise 

• Cons: + difficile pour les novices ou si le code du handler est long 

• Mettre le handler dans l’ Activity, implémenter l’interface et appeler 

setOnClickListener(this) 

• Pros: code simple 

• Cons: impossibilité de passer des arguments au handler 

• Mettre le handler dans l’ Activity, pas d’interface, spécifier la méthode avec 

android:onClick dans le main.xml 

• Pros: 1 méthode par contrôle, mais différentes méthodes pour chaque contrôle.. Plus orientée 

XML, moins de code Java 

• Cons: plus difficile pour les développeurs Java 

jeudi 26 janvier 12


BOUTON ET WIDGET 

CLICABLE 





• Buttons 


• ImageButtons chacune avec un image unique 

• ImageButtons chacune avec 3 (normal/focused/pressée) 

images 

• RadioButtons avec OnClickListener sur chaque 

• RadioButtons avec OnCheckedChangeListener sur un 

RadioGroup 

• CheckBoxes 

• ToggleButtons 

jeudi 26 janvier 12


APPROCHE GÉNÉRALE 

POUR LES WIDGET

WIDGET LECTURES COMBINED 

IN SINGLE PROJECT 

• Main screen 

• Lets user choose screens on various Widget topics 

• Other screens 

• Correspond to separate lectures. 

• One screen for lecture on Buttons, another for lecture on Spinners, another for 

number input, etc. 

• Separate layout files 

• main.xml, buttons.xml, spinners.xml, etc. See next slide. 

• Separate Java classes 

• WidgetActivity.java, ButtonActivity.java, SpinnerActivity.java, etc. 

• Shared strings file 

• strings.xml has separate sections for each lecture, but same file 

jeudi 26 janvier 12

LAYOUT FILES FOR WIDGET 

LECTURES 

• Separate layout files for each Activity 


• Gives layout for main screen. Loaded with setContentView(R.layout.main); 

• res/layout/buttons.xml 

• Gives layout for screen on Button and related Widgets. Loaded with 

setContentView(R.layout.buttons); 

• res/layout/spinners.xml 

• Gives layout for screen on Spinners (i.e., combo boxes). Loaded with 

setContentView(R.layout.spinners); 

• Two common layout attributes 

• android:layout_width, android:layout_height 

• match_parent (fill up space in enclosing View) 

• wrap_content (use natural size) 

jeudi 26 janvier 12

SWITCHING ACTIVITIES: 

SUMMARY 

• Switches Activities with Intents 

• Main screen has buttons to navigate to other Activities 

• Return to original screen with phone’s “back” button 

• Syntax required to start new Activity 

• Java 

• Intent newActivity = new Intent(this, NewActivity.class); 

• startActivity(newActivity); 

• XML 

• Requires entry in AndroidManifest.xml (which is part of downloadable Eclipse 

project for Widgets) 

• More details 

• Code and some information given in Spinner lecture 

• Even more information given in later lecture on Intents 

jeudi 26 janvier 12


OVERALL WIDGET PROJECT 

LAYOUT 

Java code 

Images and XML files that refer to sets of images. The 

layout files will refer to these images via @drawable/ 

base_file_name (e.g., @drawable/gps). The first 

ImageButton example will use an image file, and the 

second ImageButton example will use an XML file 

containing references to image files. 

Layout files. The Java code will refer to the overall layouts via 

R.layout.base_file_name (R.layout.main, R.layout.buttons, etc.). The 

Java code will refer to specific GUI elements with 

findViewById(R.id.element_id). 

Strings. The Java code will refer to these via 

getString(R.string.string_name). The layout files will refer to these with 

@string/string_name. You can also define arrays of strings here, or put the 

arrays in a separate file typically called arrays.xml. Arrays are used in the 

next lecture on Spinners. 

In order for one Activity to start another Activity in the same project, you need some 

entries in here. See Spinner lecture.


APPROACH FOR 

BUTTON-RELATED EXAMPLES


SUMMARY OF LAYOUT 

Horizontal LinearLayout (with 3 Buttons) 

Horizontal LinearLayout (with 3 ImageButtons) 

Horizontal LinearLayout (with 3 ImageButtons) 

Horizontal RadioGroup 

(with 3 RadioButtons) 

Horizontal RadioGroup 

(with 3 RadioButtons) 

Horizontal LinearLayout (with 3 CheckBoxes) 

Vertical 

LinearLayou 

Horizontal LinearLayout (with 3 ToggleButtons) 

An upcoming tutorial section gives details on using layouts. However, you can do a pretty 

lot now by knowing just two simple things: 

1) You can make some pretty complex layouts by nesting horizontal and vertical layouts 

inside each other. 

2) You can experiment interactively with the visual layout editor in Eclipse. Edit layout file 

and click on Graphical Layout. 

t

XML: LAYOUT FILE 

(RES/LAYOUT/BUTTONS.XML) 

 

 

 

 


One entry for each row in previous slide. 

These entries are shown in upcoming slides.

XML: STRINGS FILE 

(RES/VALUES/STRINGS.XML) 

 

 


 

... 

... 

... 

 

 

 

JAVA (BUTTONACTIVITY.JAVA) 

public class ButtonActivity extends Activity { 

... 






... 

} 

private void showToast(String text) { 

Toast.makeText(this, text, Toast.LENGTH_LONG).show(); 

}


BUTTON

BUTTON 

• Idea 

• A push button displaying text 

• Main Listener type 

• View.OnClickListener 

• If you specify the handler method in the XML file, you never explicitly refer to this 

Listener class. 

• Key XML attributes 

• android:text 

• The label of the button. Can also be manipulated in Java with setText and getText 

• android:onClick 

• The event handler method. As shown in event-handling lecture, you can also use 

android:id and then have Java code programmatically assign event handler. 

jeudi 26 janvier 12

XML: LAYOUT FILE ENTRY 

(PART OF RES/LAYOUT/BUTTONS.XML) 


 

 

 

 

XML: STRINGS FILE ENTRIES 

(PART OF RES/VALUES/STRINGS.XML) 


Hi! 

Bye! 

Yo! 

 

You clicked the \'%s\' Widget. 

 

These are the labels referred to in 

previous slide 

The event handler method will use 

String.format and this template to 

produce a message that will be 

shown in a Toast (short-lived 

popup message) when a Button is 

clicked.

JAVA (RELEVANT PARTS) 


private String mButtonMessageTemplate; 

} 






mButtonMessageTemplate = 

getString(R.string.button_message_template); 

} 

public void showButtonText(View clickedButton) { 

Button button = (Button)clickedButton; 

CharSequence text = button.getText(); 

String message = 

String.format(mButtonMessageTemplate, text); 

showToast(message); 

} 

This is the method specified for 

each Button via the 

android:onClick attribute in the 

layout file.


Emulator 

RESULTS 

Phone


IMAGEBUTTON 

(EACH WITH SINGLE IMAGE)

IMAGEBUTTON, VARIATION 1 


• A push button displaying an image 




• android:src 


If you just want to display an 

image, but not take action when it 

is clicked, see the ImageView 

class. 

• The image for the button. Refers to the base name (minus the extension) of an image file 

in the res/drawable folder 

• Supported formats are png, jpeg, gif, and bmp. 

You can also refer to a drawable XML file as in next example. 

• The localization lecture will talk about drawable-xdpi folders 

• Can also be set in Java with setImageDrawable 


• The event handler method




 

 

 

 

 

Refers to res/drawable/ 

android_platform.png 

Refers to res/drawable/ 

camera_phone.png 

Refers to res/drawable/gps.png




 

You clicked the ImageButton that displays %s. 

 

 

the android_platform.png image 

 

 

the camera_phone.png image 

 

 

the gps.png image 

 


String.format, this template, and 

the descriptions below to produce 

a message that will be shown in a 

Toast when an ImageButton is 

clicked.



private String mImageButtonMessageTemplate; 

} 




... 

mImageButtonMessageTemplate = 

getString(R.string.image_button_message_template); 

} 

public void showImageButton1Info(View clickedImageButton) { 

showImageButtonInfo(R.string.image_button_1_image); 

} 

... 

private void showImageButtonInfo(int imageId) { 

String image = getString(imageId); 


String.format(mImageButtonMessageTemplate, image); 


} 

This is the method specified for the first 

ImageButton via the android:onClick attribute in 

the layout file. Methods for the other 

ImageButtons are similar.


RESULTS (EMULATOR)


IMAGEBUTTON 

(EACH WITH 3 IMAGES)

IMAGEBUTTON, VARIATION 2 


• A push button displaying one of three images, depending upon the situation 




• android:src 

• The image descriptor file for the button. Refers to the base name (minus 

the .xml extension) of an XML file in the res/drawable folder 

• The file, in turn, refers to three regular images in drawable folder 

• Can also be set in Java with setImageDrawable 


• The event handler method 

jeudi 26 janvier 12

INDIVIDUAL IMAGE FILES 

VS. XML FILES 

• Individual image files 

• Android will use the same image for all states of the button (normal, focused, 

pressed) 

• Android will change the background color when focused or pressed. This affects 

the transparent pixels. 

To get images for practicing, look in android-sdk-installdir/platform-x/data/res/drawable-xdpi. 

Or, do a Google search for free icons. Also, see http:// 

developer.android.com/guide/developing/tools/ 

draw9patch.html for building your own images. 

• XML files 

• Android will use a different image for each state of the button (normal, focused, 

pressed) 

• The different images can have different foreground colors, not just different 

backgrounds. 

jeudi 26 janvier 12

IMAGE DESCRIPTOR FILE (RES/ 

DRAWABLE/BUTTON_ANDROID.XML) 

 

 

 

 

 

 


The order of the three files matters. For more detail, see http:// 

developer.android.com/reference/android/widget/ImageButton.html 

These are the actual image files 

for each of the three possible 

states of the ImageButton.




 

 

 

 

 

Refers to res/drawable/button_android.xml. This, 

in turn, refers to three regular image files. Code 

on previous slide. 

Refers to res/drawable/button_dialog.xml. This 

in turn, refers to three regular image files. 

Refers to res/drawable/button_rating_star.xml. 

This, in turn, refers to three regular image files




 

You clicked the ImageButton that displays %s. 

 

 

the Drawable defined in button_android.xml 

 

 

the Drawable defined in button_dialog.xml 

 

 

the Drawable defined in button_rating_star.xml 

 


String.format, this template, and the 

descriptions below to produce a 

message that will be shown in a Toast 

when an ImageButton is clicked. This 

is just a copy of entry already shown in 

previous ImageButton example.



private String mImageButtonMessageTemplate; 

} 




... 

mImageButtonMessageTemplate = 

getString(R.string.image_button_message_template); 

} 

public void showImageButton4Info(View clickedImageButton) { 

showImageButtonInfo(R.string.image_button_4_image); 

} 

... 

private void showImageButtonInfo(int imageId) { 

String image = getString(imageId); 


String.format(mImageButtonMessageTemplate, image); 


} 

This is the method specified for the first of 

these 3 ImageButtons via the 

android:onClick attribute in the layout file. 

Methods for the other ImageButtons are 

similar.


RESULTS (EMULATOR)


RADIOBUTTON 

(WITH EVENT HANDLER ATTACHED TO 

EACH)

RADIOBUTTON 


• A button for choosing a single option among alternatives 

• Main Listener types 


• Assign to each RadioButton if you only care about which has been pressed most 

recently. But also see upcoming example for Listener attached to the RadioGroup. 

• No need to explicitly refer to Listener when using android:onClick 

• No Listener at all 

• Some apps take no action when RadioButton is clicked, but instead query the 

RadioGroup later to find selection 


• android:text, android:onClick 

• Same as in previous examples. 

jeudi 26 janvier 12

RADIOGROUP 


• Similar to LinearLayout, but specifically for organizing RadioButtons. 

• Makes the RadioButtons exclusive (checking one causes previous selection 

to become unchecked) 


• RadioGroup. OnCheckedChangeListener 

• Assign to RadioGroup if you want to keep track of both current and previous selections 


• Mostly same as for LinearLayout 

• Use android:id if you want to programmatically set an 

OnCheckedChangeListener 

• No android:onBlah to set RadioGroup Listener in XML 

jeudi 26 janvier 12

FIRST EXAMPLE: EVENT HANDLERS 

ATTACHED TO EACH RADIOBUTTON 


• Respond to clicks on each RadioButton by showing Toast 

saying which one was pressed. 

• Approach 


• Put RadioButtons inside RadioGroup so that they are 

mutually exclusive. 

• To assign event handlers, use android:onClick for each 

RadioButton 

• No id for RadioGroup. No Listener for RadioGroup




 

 

 

 

 

This first example uses click 

handlers attached to each 

RadioButton.

STRINGS FILE AND JAVA 

• Nothing new for this example 


• Strings file 

CODE 

• Already showed button labels and 

button_message_template 

• Java code 

• Already showed makeToast and showButtonText


RESULTS (EMULATOR)


RADIOBUTTON 

(WITH EVENT HANDLER 

ATTACHED TO RADIOGROUP)

SECOND EXAMPLE: EVENT HANDLER 


ATTACHED TO RADIOGROUP 

• Respond to clicks by showing Toast saying which one was 

pressed and which one was previously selected. 

• Approach 


• Put RadioButtons inside RadioGroup so that they are mutually 

exclusive. 

• Same as last example 

• In XML, give id to RadioGroup. 

• In Java, find RadioGroup and call setOnCheckedChangeListener




 

 

 

 

 

The id is needed so that Java can get a 

reference and programmatically set the 

OnCheckedChangeListener. 

RadioButtons do not have 

android:onClick entries




 

You selected the \'%s\' RadioButton. 

There was no previous selection. 

 

 

You selected the \'%s\' RadioButton. 

Previous selection was \'%s\'. 

The event handler method will use String.format, one of these templates, the 

current selection, and the previous selection to produce a message that will be 

shown in a Toast when a RadioButton is clicked. 

Use formatted="false" if a string has more than one %s placeholder.



... 






... 

RadioGroup radioGroup = 

(RadioGroup)findViewById(R.id.radio_group); 

radioGroup.setOnCheckedChangeListener(new RadioGroupInfo()); 

} 

Continued on next page. 

RadioGroupInfo is an inner class inside 

ButtonActivity.

JAVA 

(RELEVANT PARTS, CONTINUED) 

private class RadioGroupInfo implements OnCheckedChangeListener { 

private RadioButton mLastChecked; 

private String mNewSelectionMessageTemplate; 

private String mChangedSelectionMessageTemplate; 


public RadioGroupInfo() { 

mNewSelectionMessageTemplate = 

getString(R.string.new_selection_message_template); 

mChangedSelectionMessageTemplate = 

getString(R.string.changed_selection_message_template); 

} 

Top of the inner class

JAVA 


} 

} 



public void onCheckedChanged(RadioGroup group, int checkedId) { 

RadioButton newChecked = 

(RadioButton)findViewById(checkedId); 

String message; 

if (mLastChecked == null) { // No previous selection 

message = String.format(mNewSelectionMessageTemplate, 

newChecked.getText()); 

} else { 

message = String.format(mChangedSelectionMessageTemplate, 

newChecked.getText(), 

mLastChecked.getText()); 

} 

mLastChecked = newChecked; 


} 

Bottom of the inner class. Keeps track of current 

and previous selections.


RESULTS (EMULATOR)


CHECKBOX

CHECKBOX 


• A button with two states (checked and unchecked) 

• Has visual indicator to show whether it is checked 

• In Java, use isChecked() to determine state. Use setChecked to 

programmatically change the state. 

• Same text in both states (unlike ToggleButton) 




• Take no action when CheckBox is clicked, but instead query the CheckBox 

later to find if it is checked or not 


• android:text, android:onClick 

• Same as in previous examples 

jeudi 26 janvier 12




 

 

 

 

 

Note that the class name is CheckBox, not 

Checkbox 

(as in AWT).

STRINGS FILE AND JAVA 

• Nothing new for this example 


• Strings file 

CODE 

• Already showed button labels and 

button_message_template 

• Java code 

• Already showed makeToast and showButtonText


RESULTS (EMULATOR)


TOGGLEBUTTON

TOGGLEBUTTON 


• A button with two states (checked and unchecked) 

• Has visual indicator to show whether it is checked 

• In Java, use isChecked() to determine state. Use setChecked to programmatically change the state. 

• Has different text for each state (unlike CheckBox) 




• Take no action when ToggleButton is clicked, but instead query the ToggleButton later to find if it is 

checked or not 


• android:textOn, android:textOff 

• The text for the two states. If you omit this, then the text is automatically ON and OFF (in caps) 


• Same as in previous examples 

jeudi 26 janvier 12




 

 

 

 

 

No textOn or textOff attributes, so the 

defaults of ON and OFF will be used.




Use SSL 

No SSL 

GPS On 

GPS Off 

 

You turned the ToggleButton %s. 

Label is now \'%s\'. 

 


String.format, this template, the 

state of the ToggleButton (on or 

off), and the text to produce a 

message that will be shown in a 

Toast when a ToggleButton is 

clicked.



private String mToggleButtonMessageTemplate; 




... 

mToggleButtonMessageTemplate = 

getString(R.string.toggle_button_message_template); 

}

JAVA 


This is the method specified for the 


public void showToggleButtonInfo(View clickedToggleButton) { 

ToggleButton toggleButton = 

(ToggleButton)clickedToggleButton; 

String status; 

if (toggleButton.isChecked()) { 

status = "ON"; 

} else { 

status = "OFF"; 

} 

CharSequence label = toggleButton.getText(); 


String.format(mToggleButtonMessageTemplate, 

status, label); 


} 

ToggleButtons via the android:onClick attribute in 

the layout file.


RESULTS (EMULATOR)


WRAP-UP

SUMMARY 

• Click handling is consistent among buttons 

• Button, ImageButton, RadioButton, CheckBox, ToggleButton 

• Can specify event handler method with android:onClick 

• Or can set programmatically as in events lecture 

• ImageButton 

• Can have single image or set of three. 

• Specify with android:src 

• Images and image XML files go in res/drawable folder 

• RadioGroup 

• Surrounds RadioButtons. Can have its own Listener if you need to track previous 

selection. 

• ToggleButton 

• Similar behavior to CheckBox. But has android:textOn and android:textOff instead of a 

fixed label. 

jeudi 26 janvier 12


WIDGETS: SPINNERS 

(COMBO BOXES) 





TOPICS IN THIS SECTION 

• Switching from one Activity to another 

• Spinners with choices set in XML 

• Spinners with choices set in Java 

jeudi 26 janvier 12


GENERAL APPROACH 

FOR WIDGET EXAMPLES

WIDGET LECTURES COMBINED 

IN SINGLE PROJECT 

• Main screen 

• Lets user choose screens on various Widget topics 

• Other screens 

• Correspond to separate lectures. 

• One screen for lecture on Buttons, another for lecture on Spinners, another for 

number input, etc. 

• Separate layout files 

• main.xml, buttons.xml, spinners.xml, etc. See next slide. 

• Separate Java classes 

• WidgetActivity.java, ButtonActivity.java, SpinnerActivity.java, etc. 

• Shared strings file 

• strings.xml has separate sections for each lecture, but same file 

jeudi 26 janvier 12

LAYOUT FILES FOR WIDGET 

LECTURES 

• Separate layout files for each Activity 


• Gives layout for main screen. Loaded with setContentView(R.layout.main); 

• res/layout/buttons.xml 

• Gives layout for screen on Button and related Widgets. Loaded with 


• res/layout/spinners.xml 

• Gives layout for screen on Spinners (i.e., combo boxes). Loaded with 


• Two common layout attributes 

• android:layout_width, android:layout_height 

• match_parent (fill up space in enclosing View) 

• wrap_content (use natural size) 

jeudi 26 janvier 12

STRINGS FILE FOR WIDGET LECTURES 

(RES/VALUES/STRINGS.XML) 

 

 

 

... 

... 

... 

 

 

 

 

... 

 

jeudi 26 janvier 12


SUMMARY 

• Switches Activities with Intents 

• Main screen has buttons to navigate to other Activities 

• Return to original screen with phone’s “back” button 

• Syntax required to start new Activity 

• Java 



• XML 

• Requires entry in AndroidManifest.xml (which is part of downloadable Eclipse 

project for Widgets) 


• Code shown on next few slides 

• Even more information given in later lecture on Intents 

jeudi 26 janvier 12


DETAILS 

• Java (InitialActivity.java) 

Intent newActivity = new Intent(this, NewActivity.class); 

startActivity(newActivity); 

• XML (AndroidManifest.xml) 

 


 

 

 

 


WIDGETSINITIALACTIVITY.JAVA 

public class WidgetsInitialActivity extends Activity { 





} 

} 

private void goToActivity 

(Class


ANDROIDMANIFEST.XML 

 

 

 

 

 

 

 

 

 

 

... 

 

 

 

 

 

 

 

Most parts of this file were created automatically when the Android 

project was made in Eclipse. To switch Activities yourself, cut and paste 

this code from the downloadable source, and change only android:name 

and android:label. 

jeudi 26 janvier 12


OVERALL WIDGET PROJECT 

LAYOUT 

Java code 

Images and XML files that refer to sets of images. The 

layout files will refer to these images via @drawable/ 

base_file_name (e.g., @drawable/gps). See ImageButton 

examples in lecture on buttons. 

Layout files. The Java code will refer to the overall layouts via 

R.layout.base_file_name (R.layout.main, R.layout.spinners, etc.). The 

Java code will refer to specific GUI elements with 

findViewById(R.id.element_id). 

Strings. The Java code will refer to these via 

getString(R.string.string_name). The layout files will refer to these with 

@string/string_name. You can also define arrays of strings here, or put the 

arrays in a separate file typically called arrays.xml. Arrays defined here are 

used in the first Spinner example. 

In order for one Activity to start another Activity in the same project, you need some 

entries in here. See upcoming slide.


SPINNER APPROACH 1: 

CHOICES SPECIFIED IN XML

SPINNER WITH PREDEFINED 


CHOICES 

• A combo box (drop down list of choices) 

• Similar purpose to a RadioGroup: to let the user choose 

among a fixed set of options 



• AdapterView.OnItemSelectedListener 

• AdapterView.OnItemClickedListener 

• The first is more general purpose, since it will be invoked on 

programmatic changes and keyboard events as well as clicks.

SPINNER (CONTINUED) 


• android:id 

• You need a Java reference to assign an event handler 

• android:prompt 

• The text shown at the top of Spinner when user clicks to open it. 

• Since text is not shown when the Spinner is closed, the string used for the prompt is typically also displayed in a 

TextView above the Spinner. 

• android:entries 

• An XML entry defining an array of choices. 

Can be in strings.xml or a separate file (e.g., arrays.xml) 

 

choice 1 

choice 2 

… 

 

jeudi 26 janvier 12

ONITEMSELECTEDLISTENER 

• onItemSelected 

• Invoked when the an entry is selected. Invoked once when Spinner is first 

displayed, then again for each time the user selects something. 

• Arguments 

• AdapterView: the Spinner itself 

• View: the row of the Spinner that was selected 

• int: the index of the selection. Pass this to the Spinner’s getItemAtPosition 

method to get the text of the selection. 

• long: The row id of the selected item 

• onNothingSelected 

• Invoked when there is now nothing displayed. This cannot happen due to 

normal user interaction, but only when you programmatically remove an entry. 

jeudi 26 janvier 12


(PART OF RES/LAYOUT/SPINNERS.XML) 


 

 

Same text used twice, since 

the text is hidden when the 

Spinner is closed. 

An array of entries. If you have 

lots of arrays, you typically put 

them in arrays.xml. However, 

here, it makes more sense to 

keep the array of entries in 

strings.xml with the spinner 

prompt and the spinner 

message template.




 

Current Android Vendors (Choices from XML) 

 

 

Acer 

Dell 

HTC 

Huawei 

Kyocera 

LG 

Motorola 

Nexus 

Samsung 

Sony Ericsson 

T-Mobile 

Neptune 

 

 

You selected \'%s\'. 

 


String.format, this template, and 

the current selection to produce a 

message that will be shown in a 

Toast when a Spinner selection is 

made.


public class SpinnerActivity extends Activity { 

private String mItemSelectedMessageTemplate; 






mItemSelectedMessageTemplate = 

getString(R.string.spinner_message_template); 

Spinner spinner1 = (Spinner)findViewById(R.id.spinner1); 

spinner1.setOnItemSelectedListener(new SpinnerInfo()); 

... // Code for spinner2 shown later 

} 



} 

// Continued on next slide with the SpinnerInfo inner class

JAVA 


private class SpinnerInfo implements OnItemSelectedListener { 

private boolean isFirst = true; 

} 



Don't want the Toast when the screen is first displayed, 

public void onItemSelected(AdapterView so ignore spinner, the first call to View onItemSelected. selectedView, 

Other calls are 

int selectedIndex, long due to user id) interaction. { 

if (isFirst) { 

isFirst = false; 

} else { 

String selection = 

spinner.getItemAtPosition(selectedIndex).toString(); 


String.format(mItemSelectedMessageTemplate, selection); 


} 

} 


public void onNothingSelected(AdapterView spinner) { 

// Won’t be invoked unless you programmatically remove entries 

}


RESULTS (EMULATOR)


SPINNER APPROACH 2: 

CHOICES SPECIFIED IN JAVA

SPINNER WITH CHOICES 

COMPUTED BY JAVA CODE 


• A combo box (drop down list of choices) 

• Same general purpose as previous example. However, here you 

want to programmatically compute the options to be displayed, 

possibly based on earlier user interaction. 


• AdapterView.OnItemSelectedListener 

• AdapterView.OnItemClickedListener 


• These are same as in previous Spinner example

SPINNER (CONTINUED) 


• android:id 

• You need a Java reference to specify the entries and to assign an event 

handler. 

• android:prompt 

• The text shown at the top of Spinner when user clicks to open it. 

• Since this text is not shown when the Spinner is closed, the string 

used for the prompt is typically also displayed in a TextView above 

the Spinner. 

• android:entries 

• Not used in this version. Java will compute the entries. 

jeudi 26 janvier 12

CREATING SPINNER ENTRIES 

PROGRAMMATICALLY 

• Get reference to the Spinner 

Spinner spinner = (Spinner)findViewById(R.id.spinner_id); 

• Make an ArrayAdapter 

List entries = …; // Can also use String[] 

ArrayAdapter spinnerAdapter = 

new ArrayAdapter(this, 

android.R.layout.simple_spinner_item, 

entries); 

• Specify the drop down View resource 

spinnerAdapter.setDropDownViewResource 

(android.R.layout.simple_spinner_dropdown_item); 

• Set the adapter for the Spinner 

spinner.setAdapter(spinnerAdapter); 


Predefined entry in 

Android distribution


(PART OF RES/LAYOUT/SPINNERS.XML) 


 

 

Same text used twice, since 

the text is hidden when the 

Spinner is closed. 

android:entries is not used. 

Instead of having fixed 

choices, the Java code will 

compute the options.




 

Future Android Vendors (Choices from Java) 


public class SpinnerActivity extends Activity { 

private String mItemSelectedMessageTemplate; 




// General code and code for spinner1 shown earlier 

List futureAndroidVendors = 

getFutureAndroidVendors(); 

ArrayAdapter spinner2Adapter = 



futureAndroidVendors); 

spinner2Adapter.setDropDownViewResource 


spinner2.setAdapter(spinner2Adapter); 

spinner2.setOnItemSelectedListener(new SpinnerInfo()); 

}

JAVA 



private List getFutureAndroidVendors() { 

String[] vendorArray = { "Apple", "RIM", 

"Palm", "Microsoft" }; 

List vendorList = Arrays.asList(vendorArray); 

Collections.shuffle(vendorList); 

return(vendorList); 

} The last argument to the ArrayAdapter 

constructor on previous page can be any List 

or String[]. I am randomizing the order of the 

elements to demonstrate that you can have Java 

compute the entries instead of having a fixed set of 

choiuces (in which case you would define the entries 

in the XML file as with approach 1).


RESULTS (EMULATOR)


WRAP-UP

SUMMARY 

• Spinner with fixed entries 

• Define array in strings.xml. 

• Use android:prompt and android:entries in layout file. Also assign id with 

android:id 

• Java gets ref and calls setOnItemSelectedListener 

• Spinner with computed entries 

• XML uses android:prompt and android:id 

• Java gets ref, makes ArrayAdapter with a List or String[], uses some 

predefined resource names 

• Switching Activities 



• Also requires entry in AndroidManifest.xml 

jeudi 26 janvier 12


Layouts: 

Organizing the Screen 


http://www.coreservlets.com/android-tutorial/ 

© 2011 Marty Hall 

Customized Java EE Training: http://courses.coreservlets.com/ 

Servlets, JSP, JSF 2.0, Java 6, Ajax, jQuery, GWT, Spring, Hibernate, RESTful Web Services, Android. 

Developed and taught by well-known author and developer. At public venues or onsite at your location.

Topics in This Section 

• LinearLayout 

• Strategy of nesting layouts 

• Using color files 

–And preview of Localization 

• Layout weights 

• RelativeLayout 

• TableLayout 

• hierarchyviewer 

261 

jeudi 26 janvier 12


Overview 





Main Layout Strategies 

• XML-based 

– Declare layout in res/layouts/some_layout.xml 

• Set various XML properties 

• Use visual editor in Eclipse 

– Load with setContentView(R.layout.some_layout) 

• Java-based 

– Instantiate layout, set properties, insert sub-layouts 

• LinearLayout window = new LinearLayout(this); 

• window.setVariousAttributes(…); 

• window.addView(widgetOrLayout); 

– Load with setContentView(window) 

• This tutorial 

– Uses XML-based approach. However, attributes can be adapted 

for Java-based approach. 

263 

jeudi 26 janvier 12

XML Layout Attributes 


– Each Layout class has an inner class called LayoutParams that 

defines general XML parameters that layout uses. These 

parameters are always named android:layout_blah, and usually 

have to do with sizes and margins. 

– Layout classes define more specific attributes. Many inherited 

from LinearLayout (which extends ViewGroup and View). 

• Not named beginning with “layout_” 

• Example 

… 

264 

jeudi 26 janvier 12

Commonly Used Attributes 

• Size 

– android:layout_height, android:layout_width 

• match_parent: fill the parent space (minus padding) 

– Renamed from fill_parent in older versions 

• wrap_content: use natural size (plus padding) 

• An explicit size with a number and a dimension. See margins on next slide. 

– android:layout_weight 

• A number that gives proportional sizes. See example. 

• Alignment 

– android:layout_gravity 

• How the View is aligned within containing View. 

– android:gravity 

• How the text or components inside the View are aligned. 

– Possible values 

• top, bottom, left, right, center_vertical, center_horizontal, center (i.e., center both 

ways), fill_vertical, fill_horizontal, fill (i.e., fill both directions), clip_vertical, 

clip_horizontal 

265 

jeudi 26 janvier 12


(Continued) 

• Margins (blank space outside) 

–android:layout_marginBottom, android:layout_marginTop, 

android:layout_marginLeft, android:layout_marginRight 

–Units (e.g., "14.5dp") – negative values are legal 

• dp: density-independent pixels (scaled by device resol.) 

• sp: scaled pixels (scaled based on preferred font size) 

• px: pixels 

• in: inches 

• mm: millimeters 

• Padding (blank space inside) 

266 


–android:paddingBottom, android:paddingTop, 

android:paddingLeft, android:paddingRight 

• Values are numbers with units as above


(Continued) 

• ID 

–android:id 

• Used if the Java code needs a reference to View 

• Used in RelativeLayout so XML can refer to earlier ids 

• Colors 

–android:background (color or image, for any Layout) 

–android:textColor (e.g., for TextView or Button) 

–Common color value formats 

• "#rrggbb", "#aarrggbb", "@color/color_name" 

• Click handler 

267 


–android:onClick 

• Should be a public method in main Activity that takes a View (the 

thing clicked) as argument and returns void


LinearLayout Basics 





LinearLayout 


–Put components in a single row or single column 

–By nesting, can have rows within columns, etc. 

• Most important XML attributes 

269 


–android:orientation 

• "horizontal" (a row) or "vertical" (a column) 

• horizontal is the default, so can be omitted for rows 

–android:gravity 

• How the Views inside are aligned. 

• Possible values 

– top, bottom, left, right, center_vertical, center_horizontal, center (i.e., center 

both ways), fill_vertical, fill_horizontal, fill (i.e., fill both directions), clip_vertical, 

clip_horizontal

Example Summary 

(Highly Nested Layouts) 

270 


• General Approach 

 

 

 

Example Details 

271 


Horizontal LinearLayout with gravity of center_horizontal. 

 

 

 

 

 

 

Horizontal LinearLayout with gravity of left. Otherwise almost 

same as first row. 

Remember that horizontal is the default for android:orientation, so this attribute was omitted for these 

two rows. The colors will be explained later in this tutorial.


272 


Horizontal LinearLayout. 

That Layout then contains two more horizontal LinearLayouts. The first 

(yellow) has android:layout_width of "wrap_content" and android:gravity 

of "left". The second (green) has android:layout_width of "match_parent" 

and android:gravity of "right".


273 


Horizontal LinearLayout. 

That Layout then contains three vertical nested layouts. The first (blue) is a 

LinearLayout with android:orientation of "vertical" and four Buttons inside. 

The second (violet) is a RadioGroup (similar to LinearLayout but specific to 

enclosing RadioButtons and making them mutually exclusive), also with 

android:orientation of "vertical". It has four RadioButtons inside. The third is 

a LinearLayout with android:orientation of "vertical" and four nested 

LinearLayouts inside (details on next slide). 

The first two columns (nested layouts) have android:layout_width of 

"wrap_content", and the third has android:layout_width of "match_parent".


274 


Vertical LinearLayout. 

That Layout then contains four horizontal nested layouts. The first (red) 

has android:gravity of "center_horizontal". The second (orange) has 

android:gravity of "left". The third (yellow) has android:gravity of "right". 

The fourth contains two further nested horizontal LinearLayouts. The first 

(green) has android:layout_width of "wrap_content" and android:gravity of 

"left". The second (blue) has android:layout_width of "match_parent" and 

android:gravity of "right".


275 


Button 

android:layout_width="wrap_content" 

android:layout_gravity="center_horizontal" 

android:layout_marginTop="20dp" 

Button 

android:layout_width="match_parent"



Setting Colors 

(& Localization Preview) 




Colors 


– Although colors can be defined explicitly within layout file (e.g., 

background="#ff0000"), usually more flexible to define color 

names in separate file, so they can be changed all at once. Refer 

to color with "@color/color_name". 

• Syntax 

 

#rrggbb 

… 

 

• Convention 

– Use res/values/colors.xml 

• However, any file name is legal. Sometimes it makes more sense to 

define all attributes (strings, arrays, colors) of a View in a single file 

dedicated to that view. 

277 

jeudi 26 janvier 12

Color File 

(res/values/colors.xml) 

 

 

#ff0000 

#ffa500 

#ffff00 

#008000 

#0000ff 

#ee82ee 

 

278 

jeudi 26 janvier 12

Layout File (res/layouts/ 

nested_layouts.xml) 

 

 

 

... 

 

 

 

279 

jeudi 26 janvier 12

Result 

280 

jeudi 26 janvier 12

Localization Preview 


–You can store colors or other files in res/values-xy instead of 

res/values. If the Locale is set to xy, then that file is loaded 

after the files in res/values. 

• If names match, later file overrides value from earlier file 

• Usual approach 

–Locale is set for entire phone by end user 

• Approach used here 

–Locale is set programmatically 

• Many more details 

281 


–In later lecture on localization

Setting Locale Programmatically 

• Usual purpose 

–If user sometimes wants to run app in one language and other 

times in a different language. 

• Again, more common for end user to set Locale for entire phone, 

not for individual apps. 

• Purpose here 

282 


–Set the Locale to a fake value ("qq") just so that we can 

replace colors.xml with another version that makes all the 

background colors be black.

Setting Locale Programmatically 

• Steps 

Locale locale = new Locale("es"); // Language code 

Locale.setDefault(locale); 

Configuration config = new Configuration(); 

config.locale = locale; 

context.getResources().updateConfiguration(config, 

–context above is reference to the main Activity 


283 


–http://adrianvintu.com/blogengine/post/ 

Force-Locale-on-Android.aspx 

null);

Project Layout 

284 


Sets color_1, color_2, …, color_6 to red, orange, yellow, 

green, blue, and violet. Full text of this file shown on 

earlier slide. Used if Locale is anything other than "qq". 

Sets all of color_1, color_2, …, color_6 to black. Full text 

of this file shown on next slide. Used only if Locale is 

"qq".

Localized Color File 

(res/values-qq/colors.xml) 

 

 

#000000 

#000000 

#000000 

#000000 

#000000 

#000000 

 

285 

jeudi 26 janvier 12

Main Java Code 

public class NestedLayoutsActivity extends Activity { 




setContentView(R.layout.nested_layouts); 

} 

} 

286 


... 

// Event handlers for bottom two Buttons 

There are two buttons on initial screen that invoke this same 

Activity. But, one sets the Locale to "qq" first.

Results 

287 


Locale set to anything 

other than "qq". 

Locale set to "qq".


Layout Weight 





Using android:layout_weight 


– Assign numbers for android:layout_weight. Sizes given are 

proportional to those values. 

• Steps (for heights) 

– Assign android:layout_height to 0dp 

– Use relative values for android:layout_weight 

• For example, if you have three nested entries with 

android:layout_weights of 1, 1, and 2, then they take up 25%, 25%, 

and 50% of the height of the parent. 

– Analogous approach to set widths 

• Common strategy 

– Make the layout weights add up to 100, then treat them as 

percents. So, use 25, 25, and 50 instead of 1, 1, and 2 in the 

previous example. (Same effect, but clearer.) 

289 

jeudi 26 janvier 12

Layout File (res/layouts/ 

layout_weights.xml) 

 

 

 

 

 

 

290 

jeudi 26 janvier 12

Java Code 

public class LayoutWeightsActivity extends Activity { 




setContentView(R.layout.layout_weights); 

} 

} 

291 

jeudi 26 janvier 12

Results 

292 

jeudi 26 janvier 12


RelativeLayout 





RelativeLayout 


– Give ids to 1 or more key components (id="@+id/blah") 

– Position other components relative to those components 

• Most important XML attributes 

– Aligning with container 

• android:layout_alignParentBottom (and Top, Right, Left) 

• android:layout_centerInParent (and centerHorizontal, centerVertical) 

294 


– These all take "true" or "false" as values 

– Aligning with other component 

• android:layout_alignBottom (and Top, Right, Left) 

• android:layout_toLeftOf (and toRightOf), android:layout_above (and 

below) 

– These all take existing ids as values 

» android:layout_alignBlah="@id/existing_id" (@id, not @+id)

Referring to Existing IDs 

• First component 

– 

• Second component 

– 

• Result 

295 


Button 2 

@+id for assigning a new id 

Button 1 

@id (no +) for referring to an existing id


296 



 

 

 


297 


TextView with width of match_parent and specific height. Goes 

at top since I didn't say otherwise. Has id. 

TextView with android:layout_alignTop referring to first 

component. Moved down via android:layout_marginTop 

 


298 


 

 

 

EditText with android:layout_above referring to image button. 

Has width of match_parent. 

Button with android:layout_alignBottom and android:layout_toLeftOf referring to 

image button. Has width of wrap_content. 

Button with android:layout_alignParentBottom="true" and 

android:layout_alignParentRight="true". Has an id. Has width of wrap_content. 

This is the first Button defined.


TableLayout 





TableLayout 


– Put widgets or nested layouts in a grid. No borders. 

– Like HTML tables, the number of rows and columns is 

determined automatically, not explicitly specified. 

– Components are usually placed inside TableRow 

• Most important XML attributes (TableLayout) 

– android:stretchColumns 

• An index or comma-separated list of indexes. Specifies the column or 

columns that should be stretched wider if the table is narrower than its 

parent. Indexes are 0-based. 

– android:shrinkColumns 

• Column(s) that should be shrunk if table is wider than parent. 

– android:collapseColumns 

• Column(s) to be totally left out. Can be programmatically put back in 

later. 

300 

jeudi 26 janvier 12

TableRow 


– Goes inside TableLayout to define a row. 

• Technically, elements between rows are permitted, but you can 

achieve same effect with a TableRow and android:layout_span. 

• Most important XML attributes of elements inside a 

TableRow 

– android:layout_column 

• Normally, elements are placed in left-to-right order. However, you can 

use android:layout_column to specify an exact column, and thus 

leave earlier columns empty. 

– android:layout_span 

• The number of columns the element should straddle. 

Like colspan for HTML tables. 

• There is nothing equivalent to HTML’s rowspan; you must use nested 

tables instead. See example. 

301 

jeudi 26 janvier 12


302 



 

 

… 

… 

… 

… 

 

This is why the middle column 

is wider than the other two 

columns.


303 


Two TableRows, each with 3 Buttons. No special options. 

 

 

 

 

 

 

 

 

 


304 


Button 7 uses android:layout_column="2". So, there is no entry 

at all for the middle column. 

Button 9 uses android:layout_span="2". 

 

 

 

 

 

 

 


305 


A nested table. Uses android:layout_span="2" so that it straddles two 

columns of the main table. Uses android:stretchColumns="1" so that the 

second column fills available space. 

A Button. android:layout_height is match_parent so that it is the same height 

as table to its left. There is no option similar to HTML’s colspan, so nested 

tables are needed to achieve this effect. 

 

 

 

 

 

 

 

 

 

 

 

 


The Hierarchy Viewer 





Hierarchy Viewer 


–The Android distribution includes a program called 

hieararchyviewer that will show a graphical representation of 

Views and sub-Views. Useful for debugging and 

understanding nested layouts. 

• Details 

307 


–Start app in emulator. Go to screen of interest. 

–Go to android-sdk/tools (or, put this in your PATH) 

–Type hierarchyviewer 

–Click on Focused Window, 

then press Load View 

Hierarchy button 

–Explore!

Hierarchy View for 

RelativeLayout Example 

308 


Click on an entry to show which part of screen it corresponds to, 

and to get details about the XML attributes. 

Details: http://developer.android.com/guide/developing/debugging/debugging-ui.html


Wrap-Up 





Other Layouts 

• AbsoluteLayout 

–From older versions; now deprecated; use RelativeLayout 

• FrameLayout 

–For formatting a single item. Usually used explicitly with 

TabHost. Used internally by other layouts. 

• TabHost 

–Combines tabs with switching Activities. Covered in later 

lecture on Intents and Activity switching. 

• ListView and GridView 

310 


–Not generalized layouts, but have somewhat similar role. 

Covered in later lecture.

More Reading 

• Tutorial: Declaring Layout 

–http://developer.android.com/guide/topics/ui/ 

declaring-layout.html 

• Tutorial: Hello Views 

–http://developer.android.com/resources/tutorials/views/ 

• Has sub-sections on LinearLayout, RelativeLayout, and 

TableLayout 

• Chapter: Working with Containers 

–From The Busy Coder’s Guide to Android Development by 

Mark Murphy. 

• http://commonsware.com/Android/ 

• Chapter: User Interface Layout 

311 


–From The Android Developer’s Cookbook by Steele & To

Summary 

• LinearLayout 

– Ideas 

• One row or one column. 

• Nesting is key window-layout strategy 

– Key XML attributes 

• android:orientation, android:layout_weight 

• RelativeLayout 

– Idea 

• Position later component relative to earlier one 

– Key XML attributes 

• android:layout_alignBottom (and similar), 

android:layout_toLeftOf (and similar) 

• TableLayout 

– Idea 

• Put components in a grid 

– Key XML attributes for entries inside TableRow 

• android:layout_column, android:layout_span 

312 

jeudi 26 janvier 12



Android Coding Style Conventions 







• Why follow conventions? 

• Valuable conventions 

–Ones that are widely considered good practice for any Java 

project (based on general Java industry consensus) 

• Tolerable conventions 

–Ones that do no harm, but are of questionable value 

(in Marty’s highly subjective opinion) 

• Dubious conventions 

314 


–Ones that we would have been better off without 

(in Marty’s highly subjective opinion)


Overview 





Official Android Code 

Conventions 

• Required for 

– Code contributed to Android project 

• Used in 

– All official tutorials and (supposedly) all source code 

• Suggested for 

– Code submitted to the app store 

– Any Android project 

• Details 

– http://source.android.com/source/code-style.html 

• Eclipse preferences file 

– Downloadable from coreservlets.com from this section of the 

Android Tutorial. 

• Sets spacing, brace style, and use of @Override 

316 

jeudi 26 janvier 12

Pros and Cons of Following 

Conventions 

• Pros 

– Consistent with official tutorials and Android source 

– More familiar to Android developers who join your team 

• Cons 

– Inconsistent with Java code you wrote before 

– Less familiar to other Java developers 

– Simply bothers you. 

• Java developers often have strong personal preferences 

• My recommendations 

– Most conventions are best practices anyhow 

• Definitely follow those 

– Most others are neither worse nor better than alternatives 

• Probably follow those 

– A few are (arguably) bad or at least wrong in some situations 

• Ignore those if the situation warrants it 

317 

jeudi 26 janvier 12



Conventions that are Good 

Standard Practice 

(For any Java project) 




Indentation: blocks that are nested 

more should be indented more 

• Yes 

blah; 

blah; 

for(...) { 

} 

319 


blah; 

blah; 

for(...) { 

} 

blah; 

blah; 

• No 

blah; 

blah; 

for(...) { 

blah; 

blah; 

for(...) { 

blah; 

blah; 

} 

}

Indentation: blocks that are nested the same 

should be indented the same 

• Yes 

blah; 

blah; 

for(...) { 

} 

320 


blah; 

blah; 

for(...) { 

} 

blah; 

blah; 

• No 

blah; 

blah; 

for(...) { 

} 

} 

blah; 

blah; 

for(...) { 

blah; 

blah;

Break Things into Small Pieces 

• Write short methods 

–No official limit, but try to keep methods short and focused. 

Think often about how to refactor your code to break it into 

smaller and more reusable pieces. 

• This is good advice in any language. 

• This also shows why overly strict rules on the length of 

comments can be counter productive by encouraging developers 

to write long methods to avoid writing docs. 

• Keep lines short 

321 


–They have a strict rule of 100 characters except for imports or 

comments that contain URLs or commands that cannot be 

broken up. 

• Not sure 100 is the magic number, but short lines are good 

practice anyhow.

Follow Normal Capitalization 

Rules 

• Classes start with uppercase letter 

public class SomeClass { … } 

• Constants use all caps 

public static final double GOLDEN_RATIO = 

(1 + Math.sqrt(5.0))/2; 

• Everything else starts with lowercase letter 

–Instance variables, local variables, parameters to methods, 

package names 

• Extra rule 

322 


–Use words for acronyms, not all uppercase 

• getUrl, not getURL 

– This is good advice in Web apps also

Use JavaDoc 

• Use JavaDoc from the beginning 

–Don’t wait until the code is finished. Short comments are fine, 

but use some. Explain purpose and non-obvious behavior. 

Don’t explain standard Java constructs. 

• Document every class 

/** Represents a collection of Blahs. Used to … **/ 

public class Foo { … } 

• Document anything public 

–Methods 

–Constructors 

–Instance variables (but very rare to have public ones) 

• Review Oracle JavaDoc guidelines 

• http://www.oracle.com/technetwork/java/javase/documentation/index-137868.html 

323 

jeudi 26 janvier 12

Use @Override 

• Use @Override when you override methods 

from parent class 

–Won’t be caught until run time 

public void oncreate(Bundle savedInstanceState) { 

… 

} 

–Will be caught at compile time 


public void oncreate(Bundle savedInstanceState) { 

… 

} 

• Guidelines are silent regarding interfaces 

324 


–But, in Java 6 or later, I prefer to also use @Override when 

implementing methods from interface

Use Other Standard Annotations 

when Warranted (but Rarely) 

• @Deprecated 

–If you use a deprecated method, add this annotation to your 

method. Also add @deprecated JavaDoc tag explaining why it 

was necessary to use depracated code. 

• Of course, try hard to avoid use of deprecated methods 

• @SuppressWarnings 

325 


–Generic collections are prohibited from doing extra work at 

run time, so casting to generic type can cause warning that 

Java can’t verify the types. Sometimes unavoidable 

• @SuppressWarnings("unchecked") 

• Other similar situations when making generic types 

–Android guidelines require a TODO comment in these cases, 

saying why you cannot avoid the situation

Limit the Scope of Variables 

• Use narrowest scope possible 

– Variables should be declared in the innermost block that encloses 

all uses of the variable. 

• E.g., if variable is only used inside if statement, declare it inside if 

statement. 

– Yes 

if (…) { 

double d = someCalculation(…); 

doSomethingWith(d); 

} else { 

// No use of d 

} 

– No 

double d = 0; 

if (…) { … } else { … } 

326 

jeudi 26 janvier 12

Initialize Local Variables when 

Declared 

• Initialize (almost) all local variables 

327 


–Yes 

String s = "Hello"; 

–No 

String s; 

… 

s = "Hello"; 

–Exception: try/catch blocks 

int n; 

try { 

n = Integer.parseInt(someString); 

} catch(NumberFormatException nfe) { 

n = 10; 

}

Put Braces on Conditionals 

• Always use braces for if statements 

–Even if there is only one thing to do 

• Yes 

if (…) { 

• No 

} 

doSomething(); 

if (…) 


• Guidelines give small exception 

328 


–If there is only one thing to do and it is all on one line 

• Tolerated (grudgingly?) 

if (…) doSomething();

Use TODO Comments for 

Temporary Code 

• Use “// TODO: … ” for code that needs to be 

changed later 

–Situations 

• Temporary fix 

• OK but not great 

• Works for small sizes, but bad performance in future when data 

sets get bigger. 

–Examples: 

// TODO: Switch to a Map when you have more entries 

// TODO: Remove after UrlTable2 has been checked in 

• Eclipse note 

329 


–Eclipse puts TODO in bold and puts check mark in left 

margin of code

Avoid Finalizers 

• Do not use finalize() 

–Idea 

• finalize() gets called when an object is garbage collected, so you 

can do cleanup work then (such as closing socket connections) 

–Problem 

• No guarantee when (or even if) finalizer will be called 

–Guidelines 

• Don’t use them. 

• Good news 

330 


–Finalizers have long ago fallen out of favor, and many Java 

developers don’t even know what they are.



Conventions that 

Don’t Hurt 

(No harm in following them, but 

their value is questionable) 




Put Open Braces with Preceding 

Code 

• Put { with previous line, not on its own line 

332 


–Yes 

public void foo() { 

if (...) { 


} 

} 

–No public void foo() 

{ 

} 

if (...) 

{ 


}

Indent 4 Spaces for Blocks 

• Indent 4 spaces when starting a block 

333 


–Yes 


if (...) { 


} 

} 

–No 


if (...) { 


} 

}

Indent 8 Spaces for Lines 

• Indent 8 spaces when splitting a line 

334 


–Yes 

String s = 

somethingVeryLong(…); 

–No 

String s = 

somethingVeryLong(…);

Fully Qualify Imports 

• List each class name; don’t use * 

–Yes 

• import android.widget.Button; 

• import android.widget.CheckBox; 

• import android.widget.EditText; 

–No 

• import android.widget.*; 

• Exception 

335 


–Can use * for java or javax packages 

• Permitted 

– import java.util.*;

Order Import Statements 

• First 

– Android packages 

• import android.foo.Bar; 

• Second 

– Third party packages 

• import com.coreservlets.utils.RandomUtils; 

• Third 

– Standard java or javax packages 

• import java.util.*; 

• Within each group 

– Alphabetical (uppercase Z before lowercase a) 

• Separating groups 

– Blank line between each major grouping 

336 

jeudi 26 janvier 12

Start JavaDoc Comments with 3 rd 

Person Verb 

• Examples 

–Yes 

• Represents a … 

• Responds to mouse clicks with … 

• Deletes … 

–No 

• This class … 

• This method … 

• Android’s own docs are inconsistent 

337 


–Many (most?) classes start with “This class” or similar. 

• E.g., View, Activity, LinearLayout



Questionable Conventions 

(You would have been 

better off without them) 




Start Instance Variables with 

“m” (normal) or “s” (static) 

• Use “m” for non-public, non static fields 

– “m” for “member variable” or “data member” 

• Yes 

– private String mFirstName; 

– private boolean mIsMarried; 

• No 

– private String firstName; 

– private boolean isMarried; 

• Use “s” for static (non-final) fields 

• Yes 

– private static double sBiggestRadius; 

• No 

– private static double biggestRadius; 

• Marty’s opinion 

– Results in less readable names with no real benefit 

339 

jeudi 26 janvier 12

Impact of Naming Convention 

on Constructors 

Standard Style 

public class Person { 

public String firstName, lastName; 

} 

340 

public Person(String firstName, 

String lastName) { 

this.firstName = firstName; 

this.lastName = lastName; 

} 

… 


Android Style 

public class Person { 

public String mFirstName, mLastName; 

} 

public Person(String firstName, 

String lastName) { 

mFirstName = firstName; 

mLastName = lastName; 

} 

…

Never Ignore Exceptions 

• Avoid empty catch blocks 

341 


–Yes 

try { 

… 

} catch(SomeException se) { 

doSomethingReal(); 

} 

–No 

try { 

… 

} catch(SomeException se) { } 

–Marty’s opinion 

• Usually, but not always, a good rule

Why Ignoring Exceptions Rule is 

Too Strict 

• Can make shorter code with same safety 

342 


–Android style 

int n; 

try { 

n = Integer.parseInt(…); 

} catch(NumberFormatException nfe) { 

n = 10; 

} 

–Shorter style if you could ignore exceptions 

int n = 10; 

try { 

n = Integer.parseInt(…); 

} catch(NumberFormatException nfe) { }

Why Ignoring Exceptions Rule is 

Too Strict (Continued) 

• Sometimes there is nothing to be done 

try { 

Thread.sleep(…); 

} catch(InterruptedException ie) { 

// What could you do here? 

} 

doSomethingAfterThePause(); 

343 

jeudi 26 janvier 12

Don’t Catch Generic Exception 

• List each Exception type 

–Yes 

try { 

… 

} catch(ExceptionType1 et1) { 

… 

} catch(ExceptionType2 et2) { 

… 

} 

344 


–No try { 

… 

} catch(Exception e) { 

… 

}

Why Generic Exception Rule is 

(Arguably) Too Strict 

• Listing each type is almost always best 

–So exceptions you didn’t expect don’t get caught there 

–So real failure-handling is not obscured 

• Sometimes combining is concise and safe 

345 


–E.g., if someString could be null, you could have either 

NumberFormatException or NullPointerException. But, in 

both cases, you just want to use original value for n. 

int n = 10; 

try { 

n = Integer.parseInt(someString); 

} catch(Exception e) { }


Wrap-Up 





Summary 

• Strictly follow conventions that reflect widely 

accepted best practices 

– Also, familiarize yourself with best practices. 

• All developers who have worked with Java more than two years full 

time should read Josh Bloch’s Effective Java (2 nd Edition). 

– Even experts will learn something new and valuable 

• For other conventions, if you don’t strongly object, 

follow the conventions anyhow 

– Even if you don’t see any real value 

• If convention really bothers you, ignore it 

– Assuming it is not in category of generally accepted best 

practices. Personal taste plays role in many of them. 

347 

jeudi 26 janvier 12


Intents, Intent Filters, 

and Invoking Activities: 

Part I: Using Class Name 








• Part I 

–Invoking Activities by class name 

–Defining dimensions in res/values 

–Sending data via the “extras” Bundle 

• Part II 

–Invoking Activities with a URI 

–Sending data via parameters in the URI 

• Part III 

349 


–Invoking Activities with tabbed windows 

–Defining two-image icons in res/drawable


Overview 





Idea 

• Android philosophy 

–Activities are small, single-screen units 

• Consequence 

–You need easy way to switch from one Activity to another 

• Approach: use Intent 

351 


–An abstract description of an operation to be performed 

–Intent can refer to class name of Activity or a URI 

–If a URI, then Activity registers as handler for the scheme, 

host name, or MIME type of the URI 

–In all cases, new Activity must have entry in 

AndroidManifest.xml in order to be invoked

Summary of Options 

• Invoke Activity by class name (Part I) 

–Exactly one Activity can match 

–New Activity must be in same project as original 

–Can send data via an “extras” Bundle 

• Invoke Activity by URI (Part II) 

–More than one Activity could match 

–New Activity need not be in the same project as original 

–Can send data via URI parameters or “extras” Bundle 

• Switch Activities via tabs (Part III) 

352 


–Can use class name or URI to specify Activity 


–Can send data via URI parameters or “extras” Bundle



Example Target Activity: 

Loan Payment Calculator 




Example Target Activity: 

Loan Calculator 

• Inputs 

–Loan amount 

–Interest rate (as a percent) 

–Loan period in months 

• Outputs 

–Monthly payment 

–Total payments over life of loan 

• Both are in same units 

(e.g., dollars) as the loan amount 

• Defaults 

354 


–Unless values are passed in from other Activity, uses default 

values for all inputs

Summary of Layout 

355 


Entries in first column 

are right-aligned. 

Entries in second column are 

left-aligned. They are also given 

ids so that the Java code can 

insert the text. 

This is a View with 

android:column_span="2" and 

a fixed height. 

TableLayout

XML: Layout File: First Row 

(res/layout/loan_payment.xml) 

 

 

 

 

 

 

356 


Second and third rows are very similar. Bottom two rows are almost the same except for a different textColor for the second column.

XML: Layout File: Divider 

(res/layout/loan_payment.xml) 

357 


 

 

XML: Strings File 

(res/values/strings.xml) 

 

 

Intent Filters and Activity Switching 

 

Loan Calculator: Monthly Payments 

 

Tabbed Windows 

Loan amount: 

Interest rate: 

Months: 

Monthly payment: 

Total payments: 

 

358 


The same prompts will also be used in a later input form. 

Note that represents a non-breaking space. Regular spaces are not preserved at the beginning and end of strings in Android 

resource files. Note also that is not legal here, since that is a character entity specific to HTML, not general in XML.

XML: Colors File 

(res/values/colors.xml) 

 

 

 

#d3d3d3 

#ffffff 

#ff0000 

 

359 

jeudi 26 janvier 12

XML: Dimensions File 

(res/values/dimensions.xml) 

 

 

20dp 

 

360 


If you haven't seen a dimensions file before, note that the file name is arbitrary, as with all of the resource files in res/values. However, dimensions.xml is 

a common convention. Since they come with units (dp, sp, px, in, mm), you cannot store dimensions as regular strings. Dimensions are supplied via 

"@dimen/some_name" to attributes that expect font sizes, margin sizes, widths, heights, etc. In this case, "@dimen/font_size" was supplied for the 

android:textSize attribute of each of the TextViews.

Java (LoanCalculatorActivity.java) 

public class LoanCalculatorActivity extends Activity { 

private double mLoanAmount=100000, 

mAnnualInterestRateInPercent=5.0; 

private long mLoanPeriodInMonths=360; // 30 years 

private String mCurrencySymbol = "$"; 

361 





setContentView(R.layout.loan_payments); 

setInputsFromExtras(); 

setInputsFromUri(); 

calculateAndSetOutputValues(); 

} 

We will explain setInputsFromExtras in an upcoming subsection. We will explain setInputsfromUri in Part II of the 

Intents series. For now, these methods make no changes to the instance variables, and the default values of the 

instance variables (shown at the top) will be used by calculateAndSetOutputValues.

Java, Continued 

(LoanCalculatorActivity.java) 

private void calculateAndSetOutputValues() { 

PaymentInfo paymentInfo = 

new PaymentInfo(mLoanAmount, mAnnualInterestRateInPercent, 

mLoanPeriodInMonths, mCurrencySymbol); 

TextView loanAmountDisplay = (TextView)findViewById(R.id.loan_amount); 

loanAmountDisplay.setText(paymentInfo.getFormattedLoanAmount()); 

TextView interestRateDisplay = 

(TextView)findViewById(R.id.interest_rate); 

interestRateDisplay.setText 

(paymentInfo.getFormattedAnnualInterestRateInPercent()); 

TextView loanPeriodDisplay = (TextView)findViewById(R.id.loan_period); 

loanPeriodDisplay.setText(paymentInfo.getFormattedLoanPeriodInMonths()); 

TextView monthlyPaymentDisplay = 

(TextView)findViewById(R.id.monthly_payment); 

monthlyPaymentDisplay.setText(paymentInfo.getFormattedMonthlyPayment()); 

TextView totalPaymentsDisplay = 

(TextView)findViewById(R.id.total_payments); 

totalPaymentsDisplay.setText(paymentInfo.getFormattedTotalPayments()); 

} 

362 


The math is done in the PaymentInfo class (next slides) at the top of the method, 

which in turn calls the LoanUtils class (following slides). The rest of the code just 

assigns the output values to the TextViews that are in the second column of the table 

from the layout file (res/layouts/loan_payments.xml).

Java (PaymentInfo.java) 

public class PaymentInfo { 

private final double mLoanAmount, mAnnualInterestRateInPercent, 

mMonthlyPayment, mTotalPayments; 

private final long mLoanPeriodInMonths; 

private final String mCurrencySymbol; 

} 

363 


public PaymentInfo(double loanAmount, double annualInterestRateInPercent, 

long loanPeriodInMonths, String currencySymbol) { 

mLoanAmount = loanAmount; 

mAnnualInterestRateInPercent = annualInterestRateInPercent; 

mLoanPeriodInMonths = loanPeriodInMonths; 

mCurrencySymbol = currencySymbol; 

mMonthlyPayment = LoanUtils.monthlyPayment(loanAmount, 

annualInterestRateInPercent, 

loanPeriodInMonths); 

mTotalPayments = mMonthlyPayment * mLoanPeriodInMonths; 

} 

... 

The remaining methods are just getter methods and variations of the getter methods 

that return the values as formatted strings (e.g., with commas and with exactly two 

values after the decimal point).

Java (LoanUtils.java) 

public class LoanUtils { 

public static double monthlyPayment(double loanAmount, 

double annualInterestRateInPercent, 

long loanPeriodInMonths) { 

if (annualInterestRateInPercent

Example: Results 

365 


For now, these values are fixed to the initial values set 

for the instance variables of the 

LoanCalculatorActivity. However, the upcoming 

sections will show how to pass values from another 

Activity to this one. 

Computed by LoanUtils. Formatted by 

PaymentInfo.



Invoking Activities by 

Class Name 




Summary 


– Specify class name of new Activity 

• New Activity must be in same project as original Activity 

• Syntax 

– Java (original Activity) 

367 


Intent activityIntent = new Intent(this, NewActivity.class); 

startActivity(activityIntent); 

– XML (AndroidManifest.xml) 

 

 

 

 

 



Example: 

Invoking Loan Calculator 

with Default Values 




Example: Overview 

• Initial Activity 

–Has Button that, when pressed, 

invokes the loan calculator activity 

• No data is sent to the loan calculator, 

so it will use default values for the 

loan amount, interest rate, etc. 

• Approach 

369 


–Create Intent referring to LoanCalculatorActivity.class 

• Thus, the two Activities must be in same project 

–Call startActivity 

–Put entry for LoanCalculatorActivity in AndroidManifest.xml 

• So that the initial Activity has permission to invoke the loan 

calculator

XML: Layout File 

(res/layout/main.xml) 

 

 

 

... 

 

370 


Other buttons shown later

XML: Manifest File Template 

(AndroidManifest.xml) 

 

 

 

 

 

 

 

 

 

 

... 

 

 

371 


Other Activities will be 

declared here. 

See next slide for 

LoanCalculatorActivity. 

Means that this is the 

Action that runs when 

you run the project. 

This part is generated automatically 

when you build a new Android 

project in Eclipse. 

Means that this app 

gets an icon on the 

screen of your Android 

device.

XML: Manifest File 

Action Declaration 

 

 

 

 

... 

 

 

 

 

... 

 

 

... 

 

 

372 


The "data" tag of the land the "activity" tag for the tabbed 

windows Activity are both shown later. 

Use the fully-qualified name if the new Activity is in a 

different package than the main one (i.e., the one 

listed at the top in the "manifest" start tag). 

Means that this Action 

displays data to the user, 

but is not launched as the 

initial Activity of the project. 

Means that this Action can 

be the default for certain 

types of data (shown later). 

You virtually always set action.VIEW and category.DEFAULT for 

Activities that will be invoked by other Activities.



 

 

 


 

... 

 

373 


Other strings shown earlier, and apply to the LoanCalculatorActivity, not to the initial Activity with the buttons that launch the loan calculator.

Java (IntentFilter1Activity.java) 

public class IntentFilter1Activity extends Activity { 





} 

} 

374 


public void showLoanPayments1(View clickedButton) { 

Intent activityIntent = 

new Intent(this, LoanCalculatorActivity.class); 


} 

... 

Event handler methods for other buttons shown later


375 

jeudi 26 janvier 12


Sending Data via the 

“Extras” Bundle 





Summary 


– Attach a Bundle (like a Map – see next slides) to the Intent. The 

Bundle will contain data to be used by the new Activity. 

• Syntax 



Bundle newActivityInfo = new Bundle(); 

newActivityInfo.putBlah(…); // putDouble, putString, etc. 

activityIntent.putExtras(newActivityInfo); 


– Java (new Activity) 

Intent intent = getIntent(); 

Bundle info = intent.getExtras(); 

if (info != null) { /* Retrieve vals with info.getBlah(...) */ } 

377 

jeudi 26 janvier 12

The Bundle Class: Details 

• Putting data in a Bundle 

– putBoolean, putBooleanArray, putDouble, putDoubleArray, 

putString, putStringArray, etc. 

• These all take keys and values as arguments. 

The keys must be Strings. The values must be of the standard types 

(int, double, etc.) or array of them. 

– You can also make a custom class that implements Serializable or Parceleable, then 

store instance of that class with putSerializable or putParceleable 

• Methods return void, so you cannot chain as with the putExtra method 

of Intent. 

• Retrieving data from a Bundle 

– getBoolean, getBooleanArray, getDouble, getDoubleArray, 

getString, getStringArray, etc. 

• These take keys (Strings) as arguments. 

No typecast required on retrieval. 

378 

jeudi 26 janvier 12

Option 1: Attaching Entire Bundle 

to Intent 


–Make a Bundle, add it all at once to Intent. 

• Instantiate a Bundle, then use the Bundle’s putBlah method (one 

such method for each standard type). Then, attach Bundle to 

Intent with Intent’s putExtras method. 

• Syntax 


newActivityInfo.putDouble("key1", someDouble); 

newActivityInfo.putString("key2", someString); 

… 

yourIntent.putExtras(newActivityInfo); 

379 


– Note that it is putExtras, not putExtra

Option 2: Adding One Piece of 

Data at a Time to Intent 


–Add individual pieces of data to the Intent. No need to 

explicitly create and attach a Bundle. 

• You use the overloaded “putExtra” method. The first argument is 

the key (String), and the second argument is the value, which 

can be of any standard type. However, the code that retrieves the 

value later needs to know type. 

• Syntax 

yourIntent.putExtra("key1", someDouble); 

yourIntent.putExtra("key2", someString); 

… 

– Unlike putBlah for Bundle, these putExtra methods return the Intent, so you 

can do jQuery-like chaining: 

380 


» yourIntent.putExtra(…).putExtra(…) … .putExtra(…);



Example: 


with Custom Values 








• Creates randomized data and 

sends it to the loan calculator, which 

retrieves the values and uses them 

for its calculations. 

• Approach 

382 


–Create Intent referring to LoanCalculatorActivity.class 

–Create Bundle with 3 values 

• Loan amount, interest rate, loan period 

–Attach Bundle to Intent with putExtras 


–Put entry for LoanCalculatorActivity in manifest



 

 

... 

 

... 

 

383 


First button shown earlier



 

 

 

 

... 

 

 

 

 

... 

 

 

... 

 

 

384 


No changes from previous example.



... 

} 

385 



Intent activityIntent = 


activityIntent.putExtras 

(LoanBundler.makeRandomizedLoanInfoBundle()); 


} 

... 

Code for onCreate and first button’s event handler shown earlier.

Java (LoanBundler.java) 

public class LoanBundler { 

public static Bundle makeLoanInfoBundle(double loanAmount, 


long loanPeriodInMonths, 

String currencySymbol) { 

Bundle loanInfo = new Bundle(); 

loanInfo.putDouble("loanAmount", loanAmount); 

loanInfo.putDouble("annualInterestRateInPercent", 

annualInterestRateInPercent); 

loanInfo.putLong("loanPeriodInMonths", loanPeriodInMonths); 

loanInfo.putString("currencySymbol", currencySymbol); 

return(loanInfo); 

} 

386 

jeudi 26 janvier 12

Java 

(LoanBundler.java, Continued) 

387 


public static Bundle makeRandomizedLoanInfoBundle() { 

Random randomizer = new Random(); 

double loanAmount = 25000 * (1 + randomizer.nextInt(10)); 

double interestRate = 0.25 * (1 + randomizer.nextInt(60)); 

long loanPeriod = 12 * (1 + randomizer.nextInt(30)); 

return(LoanBundler.makeLoanInfoBundle(loanAmount, 

interestRate, loanPeriod)); 

}







388 









}

Java (LoanCalculatorActivity, 

Continued) 

389 


private void setInputsFromExtras() { 


Bundle loanInfo = intent.getExtras(); 

if (loanInfo != null) { 

double loanAmount = loanInfo.getDouble("loanAmount"); 

double annualInterestRateInPercent = 

loanInfo.getDouble("annualInterestRateInPercent"); 

long loanPeriodInMonths = 

loanInfo.getLong("loanPeriodInMonths"); 

String currencySymbol = 

loanInfo.getString("currencySymbol"); 

setInputs(loanAmount, annualInterestRateInPercent, 

loanPeriodInMonths, currencySymbol); 

} 

}


Continued) 

390 


private void setInputs(double loanAmount, 


long loanPeriodInMonths, 

String currencySymbol) { 

if (loanAmount > 0) { 

mLoanAmount = loanAmount; 

} 

if (annualInterestRateInPercent > 0) { 

mAnnualInterestRateInPercent = 

annualInterestRateInPercent; 

} 

if (loanPeriodInMonths > 0) { 

mLoanPeriodInMonths = loanPeriodInMonths; 

} 

if (currencySymbol != null) { 

mCurrencySymbol = currencySymbol; 

} 

}


391 

jeudi 26 janvier 12


Wrap-Up 





More Reading 

• Tutorial: Intents and Intent Filters 

–http://developer.android.com/guide/topics/intents/ 

intents-filters.html 

• JavaDoc: Intent 

–http://developer.android.com/reference/android/content/ 

Intent.html 

• Chapters: Creating Intent Filters and 

Launching Activities and Sub-Activities 

–From The Busy Coder’s Guide to Android Development 

• http://commonsware.com/Android/ 

• Chapter: Intents and Services 

393 


–From Android in Action by Ableson et al

Summary 

• Java (original Activity) 



newActivityInfo.putBlah(…); // putDouble, putString, etc. 

activityIntent.putExtras(newActivityInfo); 


• Java (new Activity) 


Bundle info = intent.getExtras(); 

if (info != null) { /* Retrieve vals with info.getBlah(...) */ } 


 

 

 

 

394 

jeudi 26 janvier 12




Part II: Using URI 








• Part I 




• Part II 



• Part III 

396 





Overview 















398 






Invoking Activities 

with a URI 





Summary 


– Supply a URI that indirectly refers to new Activity. The new Activity registers 

as target for URIs of a certain form. 

• The originating Activity and the new Activity need not be in the same project 

• More than one Activity could match the URI. 

– If so, Android will ask you which one to use. 

• Syntax 


400 


Uri uri = Uri.parse("foo://bar.example.com/baz"); 

Intent intent = new Intent(Intent.ACTION_VIEW, uri); 



 

 

 

 

Registering to Handle URIs 

• Matching the URI itself 

–Register for a scheme and a host 

• Example URI 

– loan://coreservlets.com/calc 

• intent-filter entry 

– 

• Matching the data type 

–Register for a MIME type 

• Example URIs 

– content:// (referring to that MIME type) 

– file:// (referring to that MIME type) 

– anything:// (the Intent can call setType to specify MIME type) 

• intent-filter entry 

– 

– 

401 

jeudi 26 janvier 12

Predefined Action/URI 

Combinations 

402 


Action URI Meaning 

Intent.ACTION_CALL tel:phone_number Opens phone application and calls 

phone_number. 

Intent.ACTION_DIAL tel:phone_number Opens phone application and dials (but 

doesn’t call) phone_number. 

Intent.ACTION_DIAL voicemail: Opens phone application and dials (but 

doesn’t call) the voice mail number. 

Intent.ACTION_VIEW geo:lat,long Opens the maps application centered on 

(lat, long). 

Intent.ACTION_VIEW geo:0,0?q=address Opens the maps application centered on 

the specified address. 

Intent.ACTION_VIEW http://url 

https://url 

Intent. 

ACTION_WEB_SEARCH 

Opens the browser application to the 

specified address. 

plain_text Opens the browser application and uses 

Google search for given string. 

Table adapted from Section 4.1.5 of Android in Action by Ableson et al.



Example: 


(Data in Extras Bundle) 








• Initial Activity uses URI to indirectly invoke loan calculator 

• Initial Activity is in different project than loan calculator 

• Data is sent via extras Bundle as in previous example 

• Approach 

404 


–Create Intent with Intent.ACTION_VIEW and URI of "loan:// 

coreservlets.com/calc" 

–Create and attach Bundle as in previous example 


–Put data entry for LoanCalculatorActivity in manifest 

–


(res/layout/main.xml – 2 nd Proj.) 

 

 

 

 

 

... 

 

405 


Entries for input form and second 

button shown later.


Action Declaration (Loan Proj.) 

 

 

 

 

... 

 

 

 

 

 

 

 

... 

 

 

406 

jeudi 26 janvier 12







} 

} 

407 



Uri uri = Uri.parse("loan://coreservlets.com/calc"); 


intent.putExtras 

(LoanBundler.makeRandomizedLoanInfoBundle()); 

startActivity(intent); 

} 

... 

Code for second button (that embeds data in the URI) shown later.

Java Code Shown Earlier 

• LoanBundler 

–Makes a Bundle that stores the loan amount, interest rate, and 

loan period 

• LoanCalculatorActivity 

408 


–Calls getIntent().getExtras() and reads the data out of the 

resultant Bundle. Uses that for the initial values for the loan 

amount, interest rate, and loan period 

–Passes the values to PaymentInfo, which in turn uses 

LoanUtils to calculate monthly payment and total payments 

–Puts all five values (loan amount, interest rate, loan period, 

monthly payment, total payments) into TextViews


409 

jeudi 26 janvier 12



Sending Data via 

Parameters in the URI 




Summary 


– Embed query parameters in the URI. These parameters will represent data 

to be used by the new Activity. 

• Syntax 


411 


String address = 

"loan://coreservlets.com/calc?loanAmount=xxx&…"; 

Uri uri = Uri.parse(address); 



– Java (new Activity) 

Uri uri = getIntent().getData(); 

String loanAmountString = uri.getQueryParameter("loanAmount"); 

// Convert String to double 

...

Sending Data: 

Extras vs. URI Parameters 

• Extras Bundle 

–Pros 

• Can send data of different types. 

• No parsing required in Activity that receives the data. 

–Cons 

• More complex for originating Activity 

– Requires parsing in originating Activity if values come from EditText 

• URI parameters 

412 


–Pros 

• Simpler for originating Activity, especially if EditText used 

• More consistent with URI usage 

–Cons 

• Can send Strings only 

• Requires parsing in receiving Activity



Example: 


(Data in URI Parameters) 








• Data is extracted from textfields (EditTexts) and embedded in the 

URI that is used to invoke loan calculator 

• Approach 

414 


–Create Intent with Intent.ACTION_VIEW and URI of "loan:// 

coreservlets.com/calc?data" 

• Data is 

"loanAmount=…&annualInterestRateInPercent=…&…" 


–Put data entry for LoanCalculatorActivity in manifest 

–


(res/layout/main.xml – 2 nd Proj.) 

 

 

... 

 

 

 

 

 

 

... 

 

415 


Entry for first button shown earlier. Entries for other textfields (EditTexts) 

similar to the one shown. Entry for button at the bottom just has 

android:onClick="showLoanPayments2".



 

 


 

Loan Calculator: Monthly Payments 

 


Loan amount: 

Interest rate: 

Months: 

Monthly payment: 

Total payments: 

 

416 


The same prompts are also used in the output display. 

Note that represents a non-breaking space. Regular spaces are not preserved at the beginning and end of strings in Android 

resource files. Note also that is not legal here, since that is a character entity specific to HTML, not general in XML.


Action Declaration (Loan Proj.) 

 

 

 

 

... 

 

 

 

 

 

 

 

... 

 

 

417 


Unchanged from previous example.



... 

418 



String address = makeLoanAddressFromEditTextInputs(); 



startActivity(intent); 

} 

Code for onCreate and first button shown earlier.

Java 

(IntentFilter2Activity, Continued) 

private String makeLoanAddressFromEditTextInputs() { 

EditText loanAmountInput = (EditText)findViewById(R.id.loan_amount); 

Editable loanAmount = loanAmountInput.getText(); 

String loanAmountParam = 

String.format("loanAmount=%s", loanAmount); 

EditText interestRateInput = (EditText)findViewById(R.id.interest_rate); 

Editable interestRate = interestRateInput.getText(); 

String interestRateParam = 

String.format("annualInterestRateInPercent=%s", interestRate); 

EditText loanPeriodInput = (EditText)findViewById(R.id.loan_period); 

Editable loanPeriod = loanPeriodInput.getText(); 

String loanPeriodParam = 

String.format("loanPeriodInMonths=%s", loanPeriod); 

String baseAddress = "loan://coreservlets.com/calc"; 


String.format("%s?%s&%s&%s", baseAddress, loanAmountParam, 

interestRateParam, loanPeriodParam); 

return(address); 

} 

419 

jeudi 26 janvier 12







420 









}


Continued) 

421 


private void setInputsFromUri() { 


if (uri != null) { 

double loanAmount = getDoubleParam(uri, "loanAmount"); 


getDoubleParam(uri, "annualInterestRateInPercent"); 


getLongParam(uri, "loanPeriodInMonths"); 


uri.getQueryParameter("currencySymbol"); 



} 

} 

getQueryParameter is the builtin method of Uri. getDoubleParam and getLongParam (next slides) are 

methods of LoanCalculatorActivity that call getQueryParameter and then parse the resultant String.


Continued) 

422 


private void setInputsFromUri() { 


if (uri != null) { 

double loanAmount = getDoubleParam(uri, "loanAmount"); 


getDoubleParam(uri, "annualInterestRateInPercent"); 


getLongParam(uri, "loanPeriodInMonths"); 


uri.getQueryParameter("currencySymbol"); 



} 

}


Continued) 

423 


private double getDoubleParam(Uri uri, String queryParamName) { 

String rawValue = uri.getQueryParameter(queryParamName); 

double value = 0.0; 

try { 

value = Double.parseDouble(rawValue); 

} catch(Exception e) { } // NumberFormatEx or NullPointerEx 

return(value); 

} 

private long getLongParam(Uri uri, String queryParamName) { 

String rawValue = uri.getQueryParameter(queryParamName); 

long value = 0; 

try { 

value = Long.parseLong(rawValue); 

} catch(Exception e) { } // NFE or NPE 

return(value); 

}


424 

jeudi 26 janvier 12


Wrap-Up 





Summary 

• Java (original Activity) 


"loan://coreservlets.com/calc?loanAmount=xxx&…"; 




• Java (new Activity – can be different project) 


String loanAmountString = uri.getQueryParameter("loanAmount"); 

// Convert String to double, handle bad data 

... 


 

 

 

 

 

426 

jeudi 26 janvier 12




Part III: Using Tabs 








• Part I 




• Part II 



• Part III 

428 





Overview 















430 







Invoking Activities with 





Summary 


– Make tabbed windows. Each tab invokes a different Activity, or 

an Activity with different data. 

• Can use either specific-class approach or URI approach 

• Can send data either with an extras Bundle or in URI 

• Tab window Activity and new Activities must be in same project 

– Due to security reasons 

• Syntax 

– Java 

• Extends TabActivity. Uses TabHost and TabSpec 

432 


– Details on next slide 


• Same as shown earlier

Using TabActivity: Outline 

public class SomeActivity extends TabActivity { 




Resources resources = getResources(); 

TabHost host = getTabHost(); 

Intent intent1= ...; 

Drawable tabIcon = 

resources.getDrawable(R.drawable.icon_name); 

TabSpec tab1Spec = 

host.newTabSpec("Tab One") 

.setIndicator("Some Text", tabIcon) 

.setContent(intent1); 

host.addTab(tab1Spec); 

// Repeat for other tabs 

} 

} 

433 


Note that the setter methods for TabSpec return the TabSpec so that you can do chained assignments. 

Note also that there is no layout file when using this approach.

Defining Tab Icons 


–Although it is legal to call setIndicator(someString), the 

resultant tab looks bad because of blank space at top. So, 

more common to do setIndicator(someString, someIcon). 

• You can also do setIndicator(someView) for fancy tabs 

• Icon option 1 

–Use a single image for the icon 

• Same image used when the tab is or is not selected 

• Icon option 2 

434 


–Use 2 similar but differently colored images for the icon 

• One for when selected, one for when not

Option 1: A Single Image 

• Pros 

–Simpler 

–Text color and background color of the tab already change on 

selection, so not confusing if icon stays same. 

• Cons 

–Doesn’t look quite as good as with two images 

• Approach 

435 


–Put image file in res/drawable/some_icon.png 

–Refer to image with 

• Drawable tabIcon = 

resources.getDrawable(R.drawable.some_icon); 

–Put icon in tab label with 

• tabSpec.setIndicator("Some Text", tabIcon);

Option 2: Two Images 

(Normal and Selected) 

• Pros 

– Looks better 

• Cons 

– More work 

• Approach 

– Put image files in 

• res/drawable/some_icon_normal.png and 

• res/drawable/some_icon_selected.png 

– Make XML file (next page) 

• res/drawable/some_icon.xml 

– Refer to XML file with 

• Drawable tabIcon = 

resources.getDrawable(R.drawable.some_icon); 

– Put icon in tab label with 

• tabSpec.setIndicator("Some Text", tabIcon); 

436 

jeudi 26 janvier 12

XML Code for Dual-Image Icon 

 

 

 

 

 

 

 

437 


The file names of the two images are arbitrary. They need not end in _selected and _normal, although this 

can be a useful convention so that you know what the images are for.



Example: 


(Each Tab Sends 






–Has tabs that, when pressed, invoke the 

loan calculator with different data 

• Activity specified either with class name or URI 

– But either way, initial Activity must be in same project as new one 

• Data sent via either in extras Bundle or in URI 

• Approach 

439 


–Intents and data created in same way as before 

–Intent associated with tab via tabHost.setContent 

–Put entry for LoanCalculatorActivity in manifest 

• Same as shown previously

XML: Icon File 

(res/drawable/calculator.xml) 

 

 

 

 

 

 

 

 

440 

jeudi 26 janvier 12



 

 

 

 

... 

 

 

 

 

 

 

 

... 

 

 

441 


Unchanged from previous examples.

Java 

(TabbedActivity: Tab 1) 

public class TabbedActivity extends TabActivity { 






Intent intent1 = 


Bundle loanBundle1 = 

LoanBundler.makeLoanInfoBundle(100000, 7.5, 120); 

intent1.putExtras(loanBundle1); 

Drawable tabIcon = 

resources.getDrawable(R.drawable.calculator); 

TabSpec tab1Spec = host.newTabSpec("Tab One") 

.setIndicator("10 Year", tabIcon) 



442 


This first tab uses an Intent that specifies the Activity by class name. 

It sends data via an extras Bundle. Reminder: there is no layout file when using TabActivity.

Java 


443 


Uri uriTwentyYear = 

Uri.parse("loan://coreservlets.com/calc"); 


new Intent(Intent.ACTION_VIEW, uriTwentyYear); 

Bundle loanBundle2 = 

LoanBundler.makeLoanInfoBundle(100000, 7.5, 240); 

intent2.putExtras(loanBundle2); 

tabIcon = resources.getDrawable(R.drawable.calculator); 

TabSpec tab2Spec = host.newTabSpec("Tab Two") 




This second tab uses an Intent that specifies the Activity with a URI. 

It sends data via an extras Bundle.

Java 


444 


String baseAddress = "loan://coreservlets.com/calc"; 


String.format("%s?%s&%s&%s", 

baseAddress, 

"loanAmount=100000", 

"annualInterestRateInPercent=7.5", 

"loanPeriodInMonths=360"); 

Uri uriThirtyYear = Uri.parse(address); 


new Intent(Intent.ACTION_VIEW, uriThirtyYear); 

tabIcon = resources.getDrawable(R.drawable.calculator); 

TabSpec tab3Spec = host.newTabSpec("Tab Three") 




This second tab uses an Intent that specifies the Activity with a URI. 

It sends data via parameters embedded in the URI.


445 

jeudi 26 janvier 12


Wrap-Up 





Summary 

• Java (extends TabActivity) 


Intent intent1= ...; // Refers to Activity in same project 

Drawable tabIcon = resources.getDrawable(R.drawable.some_icon); 

TabSpec tab1Spec = host.newTabSpec("Tab One") 

.setIndicator("Some Text", tabIcon) 



// Repeat for other tabs 

• Icon (res/drawable/some_icon.xml) 

 

 

 

 

 

447 

jeudi 26 janvier 12


Localization and Resources 








• Localization overview 

• Localization options 

–Language 

–Country/region language variations 

–Screen orientation 

–Display resolution 

–Others 

• Configuration qualifier precedence 

449 

jeudi 26 janvier 12


Overview 





Big Idea 

• Good news 

– Android’s use of resource files (res/layout/main.xml, res/values/ 

strings.xml, etc.) simplifies GUI development 

• Bad news 

– Descriptions in English won’t work in German 

– What fits in portrait orientation won’t fit in landscape 

– Images for high-density screens are too large for low-density ones 

• Solution 

– Make multiple layout and resource files 

• For different languages, orientations, etc. 

– Have Android automatically switch among or combine them 

• Notes 

– Localization sometimes called L10N (L, 10 letters, N) 

– Also sometimes called Internationalization (I18N) 

451 

jeudi 26 janvier 12


Process 

• Make qualified versions of resource files 

– Find the settings that affect your application 

• Language, orientation, touchscreen type, dock mode, etc. 

– Find qualifier names that correspond to each setting 

• Language: en, en-rUS, es, es-rMX, etc. 

• Screen orientation: port, land 

• Display density: xhdpi, hdpi, mdpi, ldpi 

• Dock mode: car, desk 

• Etc. 

– Append qualifier names to folder names 

• res/values/strings.xml, res/values-es/strings.xml, 

res/values-es-rMX/main.xml 

• res/layout/main.xml, res/layout-land/main.xml 

• Load the resource normally 

– R.string.title, R.layout.main, etc. 

– Android will switch among layout files automatically 

– Android will combine values files automatically 

• More specific values will replace earlier ones 

452


Language 





Overview 


–Change the display based on the user’s language 

• Resources that typically change 

–Strings (in res/values, e.g., in res/values/strings.xml) 

–Images (in res/drawable – image file or XML file) 

–Colors (in res/values, e.g., in res/values/colors.xml) 

–Audio and video (in res/raw) 

–Dimensions, arrays, and styles (in res/values, e.g., …/ 

dimens.xml, …/arrays.xml, …/styles.xml) 

• Resources that do not usually change 

454 


–Layout files (in res/layout) 

• Changing layout based on language makes for hard-to-maintain 

apps. See best-practices slide.

Steps 

• Make multiple folders with language codes 

– res/values, res/values-es, res/values-ja, etc. 

• Language codes are specified by ISO 639-1 

– http://en.wikipedia.org/wiki/ISO_639-1 

• Define all strings in default folder 

– In res/values, define all names 

• Use the most common language 

– E.g., res/values/strings.xml (or other name in res/values) 

Apple 

Welcome! 

• Use similar approach for colors, images, etc. 

– Use res/values/ for all colors, dimensions, arrays, etc. 

– Use res/drawable for all image files 

– Use res/raw for all audio and video files 

455 

jeudi 26 janvier 12

Steps (Continued) 

• In XML, refer to base string name 

– someAttribute="@string/company_name" 

– someAttribute="@ string/welcome_message" 

• No reference to folder or language. 

• Android will provide the proper version automatically. It first loads values 

from res/values/strings.xml, then loads values from res/values-es/ 

strings.xml. Any names in second file that are common to first file are 

replaced. 

• In Java, refer to base string name 

– getString(R.string.company_name) 

– getString(R.string.welcome_message) 

• No reference to folder or language. Same process as above. 

• Use similar approach for other resources 

– XML: @drawable/flag, @color/default_foreground, etc. 

– Java: R.drawable.flag, R.color.default_foreground, etc. 

457 

jeudi 26 janvier 12

How User Changes Device 

Language 

• On phone (or other physical Android device) 

458 


–Go to home screen, press Menu button, select Settings 

• (Most people also have the Settings app on desktop) 

–Choose Language and Keyboard 

–Choose Select locale at the top 

• Most phones will have a very 

limited number of choices, 

based on what device 

manufacturer supports 

– Android cannot (easily) use 

localization within apps unless 

entire OS supports that language. 

Major Android failing. 

– But, see upcoming slides on 

programmatic Locale changes.

How User Changes Device 

Language 

• On emulator 

459 


–Option 1: use same approach as 

above 

• You will have a limited number of 

choices, based on what was 

installed in your Android SDK image. 

But, it will almost certainly be a 

bigger set than the real phone. 

–Option 2: use Custom Locale app 

on app screen 

• If Locale you want is not there, add it 

(even regional ones) 

• Long-press the Locale to choose it 

To go to app screen, go to home 

screen and press this.

Example: The Android Resort 


–Make an app that advertises a luxury resort where visitors can 

sit inside all day and play with their smart phones 

• Approach 

460 


–res/values/strings.xml defines 

• resort_name, welcome, our, pool, reserve, confirmed 

–res/values-es/strings.xml defines 

• welcome, our, pool, reserve, confirmed 

– Does not redefine resort_name 

–Also uses dimensions, colors, images, and layout files 

• But these do not change based on language, so localized 

versions are not shown until a later example

Strings File: English/Other 


 

 

AndroidResort.com 

Welcome to 

Our 

swimming pool 

Reserve Now! 

Registration Confirmed 

 

461 


Reminder from intents lecture: is a non-breaking space. 

Android does not preserve whitespace at the beginning and end of 

strings in resource files.

Strings File: Spanish 

(res/values-es/strings.xml) 

 

 

Bienvenido a 

Nuestra 

piscina 

¡Reserva Ahora! 

Registro Confirmado 

 

462 


Note that there is not an entry for resort_name. 

The value from res/values/strings.xml carries over.

Layout File res/layout/main.xml 

(No Language-Based Versions) 

 

 

 

 

 

 

 

 

 

 

 

463 

jeudi 26 janvier 12

Manifest File 

(No Language-Based Versions) 

 

 

 

 

 

 

 

 

 

 

 

 

464 

jeudi 26 janvier 12

Java Code 

public class AndroidResortActivity extends Activity { 





} 

} 

465 


public void confirmRegistration(View clickedButton) { 

String message = getString(R.string.confirmed); 


} 



}


466 


Uses the named strings via getString(R.string.string_name). Uses same 

syntax regardless of whether the string came from values/strings.xml or 

was overridden in values-es/strings.xml 

Uses the named strings via @string/string_name. Uses same syntax regardless of 

whether the string came from values/strings.xml or was overridden in values-es/ 

strings.xml 

Defines all named strings. Applies to all languages except Spanish, and even one of 

the names applies to Spanish, since the Spanish version does not override 

resort_name. 

Overrides the named strings that are different in Spanish.

Results: English 

467 


res/values/strings.xml 

• resort_name 

• welcome 

• our 

• pool 

• reserve 

• confirmed 

This is the result not just for English, but for any language other than Spanish.

Results: Spanish 

468 


res/values/strings.xml 

• resort_name 

res/values-es/strings.xml 

• welcome 

• our 

• pool 

• reserve 

• confirmed

Best Practices 

• Provide unlocalized defaults for all values 

–So if Locale is unexpected, it displays in default language 

• E.g., if English is main language, use res/values, not res/valuesen. 

Also, test your app in unsupported Locale. 

• Use graphical layout editor for testing 

–For layout file, it lets you interactively change language, 

screen orientation, display resolution, and more 

• Avoid changing layouts based on language 

469 


–Might be necessary in some cases (e.g., US English asks for 

given name first and family name second, whereas Indian 

English asks for them in opposite order). However, makes for 

hard-to-maintain code. 

• Consider putting the logic in Java code instead

Graphical Layout Editor in 

Eclipse (Editing main.xml) 

470 


Changing display resolution 

Changing screen orientation 

Changing language (Eclipse will list all languages your 

app supports, based on your folder names) 

Also lets you change dock 

mode, day/night mode, style 

(theme), and Android version.

Changing the Language 

Programmatically 

• Letting user change Locale 

– Pros 

• Expected/recommended Android approach 

• All localization works gracefully 

– Cons 

• Can only use languages that device manufacturer supports for the 

entire OS 

• Requires user to take several steps they might not know 

• Changing Locale in your code 

– Pros 

• Can use any language you want 

• Can let user set language in app with simple button 

– Cons 

• Not expected/recommended approach 

• Settings do not live across app restarts (including rotations!), so 

requires you to remember and reuse it. 

471 

jeudi 26 janvier 12

Changing the Language 

Programmatically: Code 

• Steps 

Locale locale = new Locale("es"); // Language code 

Locale.setDefault(locale); 

Configuration config = new Configuration(); 

config.locale = locale; 

context.getResources().updateConfiguration(config, 

–context above is reference to the main Activity 


472 


–http://adrianvintu.com/blogengine/post/ 

Force-Locale-on-Android.aspx 

null);


Region 





Idea 

• Values can be specific to region 

– Not only to general language 

– Examples 

• Words 

– US English: garbage truck 

– Australian English: rubbish lorry 

• Images 

– Flag of the country 

• Colors 

– Colors matching flag 

• Audio files 

– US English: Yankee Doodle 

– Australian English: Waltzing Matilda 

• Good news 

– Android lets you define res/values-en-au, etc. 

• Bad news 

– Most phones support few or no regional settings 

474 

jeudi 26 janvier 12

Steps 

• Put default values in res/values 

–As before. List all the names 

• Put general lang. values in res/values-xx 

–Where xx is ISO 639-1 language code as before 

–List only the names that change from the default language 

• Put regional values in res/values-xx-rYY 

–Where xx is the language code and YY is the country code 

(case insensitive). Note the “r” for “region”. 

• Codes are specified by ISO 3166-1 

– http://en.wikipedia.org/wiki/ISO_3166-1_alpha-3 

–List only the names that change from the base language 

• Process 

475 


–Android will load from most general to most specific



–Add support for Mexican Spanish, which uses “alberca” 

instead of “piscina” for “swimming pool”. 

• Approach 

476 


–res/values/strings.xml defines 

• resort_name, welcome, our, pool, reserve, confirmed 

–res/values-es/strings.xml defines 

• welcome, our, pool, reserve, confirmed 

–res/values-es-rMX/strings.xml defines 

• pool

Strings File: English/Other 


 

 

AndroidResort.com 

Welcome to 

Our 

swimming pool 

Reserve Now! 

Registration Confirmed 

 

477 

jeudi 26 janvier 12

Strings File: General Spanish 

(res/values-es/strings.xml) 

 

 

Bienvenido a 

Nuestra 

piscina 

¡Reserva Ahora! 

Registro Confirmado 

 

478 

jeudi 26 janvier 12

Strings File: Mexican Spanish 

(res/values-es-rMX/strings.xml) 

 

 

alberca 

 

479 

jeudi 26 janvier 12


480 


Uses the named strings via getString(R.string.string_name). Uses same 

syntax regardless of whether the string came from values/strings.xml or 

was overridden in values-es/strings.xml or values-es-rMX/strings.xml. 

Uses the named strings via @string/string_name. Uses same syntax regardless of 

whether the string came from values/strings.xml or was overridden in values-es/ 

strings.xml or values-es-rMX/strings.xml. 

Defines all named strings. Applies to all languages except Spanish, and even one of 

the names applies to Spanish, since the Spanish versions do not override 

resort_name. 

Overrides the named strings that are different in Spanish. 

Overrides the named strings that are different in Mexican Spanish from in 

general Spanish.

Results 

481 


Any language other than Spanish General Spanish Mexican Spanish


Screen Orientation 





Overview 


–Change the display based on whether the device is being held 

in portrait or landscape mode. 


–Layout files (in res/layout) 


–Dimensions (in res/values, e.g., …/dimens.xml) 

–Video (in res/raw) 


483 


–Strings (in res/values, e.g., in res/values/strings.xml) 

–Colors (in res/values, e.g., in res/values/colors.xml) 

–Audio (in res/raw)

Steps 

• Make two folders: default and landscape 

–res/layout and res/layout-land 

• You can do layout-port, but more common to use default 

• Define different layouts (of same name) in 

each 

–For portrait mode 

• res/layout/main.xml (and maybe other names) 

–For landscape mode 

• res/layout-land/main.xml (and maybe other names) 

• Use similar approach for dimensions, images, 

etc. 

–Use res/values/ and res/drawable for portrait mode and for 

things that are the same in both orientations. 

484 


–Override in res/values-land and res/drawable-land

Steps (Continued) 

• In XML, refer to base dimensions or images 

–textSize="@dimen/heading_size" 

–src="@ drawable/some_image" 

• No reference to folder or orientation. Android handles. 

• In Java, refer to base layout name 

485 


–setContentView(R.layout.main) 

• Android will provide the proper version automatically. For layout 

files, only one version applies. For values files, names are 

combined as before, with later values overriding earlier values of 

the same name.

Precedence of Folder Names 


– Many folders with a single qualifier could apply (values, values-es, 

values-land, etc.). 

– You can also combine the names (e.g., values-es-land) 

• Language must be first, so use values-es-land, not values-land-es 

– So, which entries win? 

• Layout files and drawable files 

– Only one file applies. Language entries win over screen orientation, so if 

there is layout-es and layout-land, and you are in both Spanish and 

landscape, layout-es wins 

• But, remember advice to avoid language-based layouts 

• Values files 

– Many files may apply. They are loaded from least specific to most 

specific, and later values override earlier ones of the same name. 

Language is more specific than orientation. 

486 

jeudi 26 janvier 12

How User Changes Screen 

Orientation 

• On phone (or other Android device) 

–Physically rotate the device 

• On emulator 

–Hit Control-F12 or 

–Hit 9 on the number keypad (Num Lock must be off) 

• In visual layout editor in Eclipse 

487 


–Choose Portrait or Landscape from the second combobox 

above the display



–Use two layouts: one for portrait and one for landscape 

–Change font sizes for heading depending on orientation 

–Keep support for English and Spanish 

• Approach 

488 


–res/layout/main.xml defines layout for portrait mode 

–res/layout-land/main.xml defines layout for landscape 

–res/values/dimens.xml defines font size for portrait 

–res/values-land/dimens.xml defines size for landscape 

–res/values, res/values-es, and res/values-es-rMX define strings 

and colors as shown previously

Layout File: Portrait Mode 


 

 

 

 

 

 

 

 

 

 

 

489 

jeudi 26 janvier 12

Layout File: Landscape Mode 

(res/layout-land/main.xml) 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

490 


Recall that horizontal is the default orientation.

Dimensions File: Portrait Mode 

(res/values/dimens.xml) 

 

 

32dp 

22dp 

 

491 

jeudi 26 janvier 12

Dimensions File: Landscape 

(res/values-land/dimens.xml) 

 

 

26dp 

24dp 

 

492 

jeudi 26 janvier 12


493 


Defines the layout for portrait mode. Uses @dimen/heading_size and @dimen/ 

body_size, which are defined in res/values/dimens.xml 

Defines the layout for landscape mode. Uses @dimen/heading_size and @dimen/ 

body_size, which are defined in res/values-land/dimens.xml 

Defines heading_size and body_size for use in portrait mode. 

Defines heading_size and body_size for use in landscape mode.

Results: English 

(Really Non-Spanish) 

494 

jeudi 26 janvier 12

Results: General Spanish 

495 

jeudi 26 janvier 12

Results: Mexican Spanish 

496 

jeudi 26 janvier 12

Preventing Screen Rotations 

• Issue 

–Screen rotations usually require a new layout 

–They also cause the app to be shutdown and restarted 

• Handling this will be discussed in the next lecture 

• Problem 

–What if you do not have landscape layout? 

–Or have not yet handled shutdown and restart? 

• Solution 

497 


–Put an entry in AndroidManifest.xml saying that app runs 

only in portrait mode (or only in landscape mode) 

Example: Screen from Widgets 

Lecture (Manifest File) 

 

 

 

 

... 

 

 

 

 

 

 

... 

 

 

498 

jeudi 26 janvier 12


(in Landscape Mode) 

499 

jeudi 26 janvier 12


Display Resolution 





Overview 


–Change images based on the resolution of the display 



–Video (in res/raw) 


501 


–Dimensions 

• If you use xxdp, then it will scale to screen resolution 

– There are also small, normal, large, and xlarge qualifiers for screen size. Even 

with xxdp, you might want to adapt to those 

• But if you use yypx or zzin or aamm, then you need to change 

the dimensions to match the resolution 

–Layout files, strings, colors, audio, etc.

Common Approaches 

• Alternative 1: Default plus two others 

– drawable 

• Put images for high-res and extra-high-res (dots-per-inch) here 

– drawable-mdpi 

• Put images for medium-res (dots-per-inch) here 

– drawable-ldpi 

• Put images for low-res (dots-per-inch) here 

• Alternative 2: Three res-specific folders 

– drawable-hdpi 

• Put images for high-res and extra-high-res (dots-per-inch) here 

– drawable-mdpi 

• Put images for medium-res (dots-per-inch) here 

– drawable-ldpi 

• Put images for low-res (dots-per-inch) here 

502 

jeudi 26 janvier 12

Meanings of Resolution Qualifiers 

• xhdpi (extra-high dpi) 

–320 dots per inch 

–But, Android uses best match, so if you put images in 

drawable-hdpi and it is extra-high, images are still used. 

• Another common option is to use a single set of images for both 

extra-high and high, and put them in drawable 

• hdpi (high dpi) 


• mdpi (medium dpi) 


• ldpi (low dpi) 

503 


–120 dots per inch

Best Practices 

• For small icons (e.g., for ImageButton) 

–Use multiple versions 

–Realize that the size will be slightly different on different 

displays, so leave enough room to compensate 

• For larger images (e.g., for ImageView) 

504 


–Use multiple versions 

–Scale the image if it is larger than the available space 

Precedence of Folder Names 


– You may have many folders that apply 

• drawable, drawable-mdpi, drawable-es, drawable-es-land-hdpi… 

– So, which entries win? 

• Precedence rules 

505 


– Language is highest precedence 

• drawable-es wins over drawable-land or drawable-mdpi 

– Orientation is second highest 

• drawable-land wins over drawable-hdpi 

– Density is last (of these three) 

• But, try to chain the qualifiers so there is never a conflict. 

– drawable-land-hdpi, drawable-land-mdpi, etc.



–Have three versions of the swimming pool image: for low, 

medium, and high (or extra-high) resolution devices 

• Approach 

506 


–drawable/android_resort_pool.jpg 

• For high-res or extra-high-res devices 

–drawable-mdpi/android_resort_pool.jpg 

• For medium-res devices 

–drawable-ldpi/android_resort_pool.jpg 

• For low-res devices 

–Scale the image so that if it is still too big, it will not be 

cropped

Results (Choosing Different 

Densities in Visual Editor) 

507 

jeudi 26 janvier 12


Wrap-Up 





Configuration Types 

• Most common qualifiers (in order of precedence) 

– Language and region 

• es, es-rMX, etc. 

– Screen size 

• small, normal, large, xlarge 

– Orientation 

• port, land 

– Resolution (density) 

• ldpi, mdpi, hdpi, xhdpi 

– Touchscreen type 

• notouch, stylus, finger 

– Full list 

• http://developer.android.com/guide/topics/resources/ 

providing-resources.html 

• Using multiple qualifiers 

– Order of qualifiers must match precedence order above 

• values-es-port-ldpi, not values-es-ldpi-port or values-port-es-ldpi 

509 

jeudi 26 janvier 12

More Reading 

• Developer’s Guide: Localization 

–http://developer.android.com/guide/topics/resources/ 

localization.html 

• Developer’s Guide: Application Resources 

–http://developer.android.com/guide/topics/resources/ 

• Tutorial: Hello L10N 

–http://developer.android.com/resources/tutorials/ 

localization/index.html 

• Chapter: Localization 

510 


–From Android in Action by Ableson et al

Summary 

• Language 

–Provide multiple versions of strings file 

• Maybe images, colors, and sounds as well 

• Default folder should provide values for all names 

• Screen orientation 

–Provide multiple versions of layout files 

• Maybe dimension files and images as well 

• Screen density 

–Provide multiple versions of images (drawable files) 

• Maybe videos and dimension files as well 

• Best practices 

511 


–Test in all combinations, esp. unexpected languages 

–Use Eclipse graphical layout editor for initial testing


Handling Screen Rotations and 

Other App Restarts 








• Motivation 

• Saving data 

• The Bundle class 

• Retrieving data 

• Activity lifecycle 

513 

jeudi 26 janvier 12


Overview 






• Android can shut down and restart your app 

– When you rotate the screen 

– When you change languages 

– When app is in background and Android is short on memory 

– When you hit the Back button 

• Problem 

– You risk losing user changes 

• Solution 

– Save data in a Bundle in onSaveInstanceState 

– Read data out of Bundle in onRestoreInstanceState 

(or in onCreate) 

• Does not handle Back button scenario. 

App restarts from scratch with no saved data in that case. 

515 

jeudi 26 janvier 12

Reminder: 

Preventing Screen Rotations 

• Issue 

–Screen rotations usually require a new layout 

–They also cause the app to be shutdown and restarted 

• Handling this is the topic of this lecture 

• Problem 

–What if you do not have landscape layout? 

–Or have not yet handled shutdown and restart? 

• Solution 

516 


–Put an entry in AndroidManifest.xml saying that app runs 

only in portrait mode (or only in landscape mode). 


Steps 





Summary: Saving Data 

• Override onSaveInstanceState 

– And pass the Bundle to the superclass method 

protected void onSaveInstanceState(Bundle outState) { 

super.onSaveInstanceState(outState); 

outState.putBlah(someData); 

} 

• Called 

– When user rotates screen 

– When user changes language 

– When app is hidden and Android needs the memory 

• Not called 

– When user hits Back button 

• Note 

– Superclass method automatically stores state of GUI widgets (EditText 

data, CheckBox state, etc.) 

518 

jeudi 26 janvier 12

Summary: Restoring Data 

• Override onRestoreInstanceState 

–Pass Bundle to superclass method 

–Look for data by name, check for null, use the data 

protected void onRestoreInstanceState(Bundle savedInstanceState) { 

super.onRestoreInstanceState(savedInstanceState); 

SomeType data = savedInstanceState.getBlah(key); 

if (data != null) { doSomethingWith(data); } 

} 

• Called 

–Any time app is restarted after onSaveInstanceState 

• Note 

519 


–The same Bundle is passed to onCreate. 

–Superclass method automatically restores widget state

The Bundle Class: Details 

• Putting data in a Bundle 

– putBoolean, putBooleanArray, putDouble, putDoubleArray, 

putString, putStringArray, etc. 

• These all take keys and values as arguments. 

The keys must be Strings. The values must be of the standard types 

(int, double, etc.) or array of them. 

– putSerializable, putParceleable 

• Lets you store custom objects. Note that ArrayList and most other 

builtin Java types are already Serializable 

• Retrieving data from a Bundle 

– getBoolean, getBooleanArray, getDouble, getDoubleArray, 

getString, getStringArray, etc. 

• No typecast required on retrieval. Numbers are 0 if no match. 

– getSerializable, getParceleable 

• Typecast required on retrieval. Values are null if no match. 

520 

jeudi 26 janvier 12


Example 





Loan Payment Comparisons 


–User can enter various interest rates to compare the resultant 

monthly and total payments for a $100K, 

30 year, fixed-rate loan 

–Different layouts for portrait and landscape modes 

–Uses the PaymentInfo class that was shown in the first Intents 

lecture 

• Approach 

522 


–Keep an ArrayList of PaymentInfo 

• Also put results in a TableView 

–In onSaveInstanceState, store the ArrayList 

–In onRestoreInstanceState, retrieve the ArrayList 

• Also put results in a TableView



 

 

 

 

 

... 

 

 

 

(Has heading and divider, but no body rows.) 

 

 

523 

jeudi 26 janvier 12


(res/layout-land/main.xml) 

 

 

 

 

 

 

... 

 

 

 

 

(Has heading and divider, but no body rows.) 

 

 

524 

jeudi 26 janvier 12

Values Files 


–Defines intro text, prompt, table headings, 

and button label. 

• Used in both portrait and landscape mode. 

• res/values/dimens.xml 

–Gives font sizes. 

• Used in portrait mode. 

• res/values-land/dimens.xml 

525 



• Used in landscape mode.

Core Java Code 

public class RotationsActivity extends Activity { 

private final static double LOAN_AMOUNT = 100000; 

private final static long LOAN_PERIOD = 360; // In months 

private TableLayout mPaymentsTable; 

private EditText mInterestRateField; 

private float mTableSize; 

private ArrayList mRowData = 

new ArrayList(); 

526 






mPaymentsTable = (TableLayout)findViewById(R.id.payment_table); 

mInterestRateField = 

(EditText)findViewById(R.id.interest_rate_field); 


mTableSize = resources.getDimension(R.dimen.table_body_size); 

} 

Looks up the ID of the table so that it can later programmatically add rows to it. Note that the 

PaymentInfo data is declared as ArrayList instead of List. This is because we will later store it in a 

Bundle, and ArrayList is Serializable whereas List is not.

Core Java Code (Continued) 

527 


// Attached to the Button via the android:onClick attribute 

public void addComparisonRow(View clickedButton) { 

double interestRate = 5.0; 

try { 

interestRate = Double.parseDouble 

(mInterestRateField.getText().toString()); 

} catch(Exception e) {} 

PaymentInfo info = 

new PaymentInfo(LOAN_AMOUNT, interestRate, LOAN_PERIOD); 

mRowData.add(info); 

addRow(info); 

mInterestRateField.setText(""); 

} 

Reads the textfield value, converts to a number (5.0 default if field is empty or value is illegal), computes payment info, 

stores payment info in an ArrayList, then calls code to add data to bottom of table.

Core Java Code (Continued) 

528 


private void addRow(PaymentInfo info) { 

TableRow row = new TableRow(this); 

row.addView(makeColumn 

(info.getFormattedAnnualInterestRateInPercent())); 

row.addView(makeColumn(info.getFormattedMonthlyPayment())); 

row.addView(makeColumn(info.getFormattedTotalPayments())); 

mPaymentsTable.addView(row); 

} 

private TextView makeColumn(String text) { 

TextView col = new TextView(this); 

col.setGravity(Gravity.RIGHT); 

col.setTextSize(mTableSize); 

col.setText(text); 

return(col); 

} 

Creates a TableRow and inserts it into bottom of TableView.

Results (Without Saving State) 

529 


User enters some interest rates to 

get this result 

After entering the data as on the left, 

user rotates the screen. Data is lost!

Java Code: Saving State 

530 



protected void onSaveInstanceState(Bundle outState) { 

super.onSaveInstanceState(outState); 

outState.putSerializable("rowData", mRowData); 

} 

ArrayList is already Serializable. But, I had to make PaymentInfo (the data inside) Serializable as well.

Java Code: Saving State 

531 



protected void onRestoreInstanceState(Bundle savedInstanceState) { 

super.onRestoreInstanceState(savedInstanceState); 

@SuppressWarnings("unchecked") 

ArrayList rowData = 

(ArrayList) 

savedInstanceState.getSerializable("rowData"); 

if (rowData != null) { 

mRowData = rowData; 

for(PaymentInfo info: rowData) { 

addRow(info); 

} 

} 

} 

Since generics are implemented by erasure (all work done at compile time, no work done at run time), casting to ArrayList will 

give a warning that Java cannot verify that the list contains only Blahs. So, suppress that warning.

Java Code: PaymentInfo 

public class PaymentInfo implements Serializable { 

private final double mLoanAmount, 

mAnnualInterestRateInPercent, 

mMonthlyPayment, mTotalPayments; 

private final long mLoanPeriodInMonths; 

private final String mCurrencySymbol; 

} 

532 


// Calculates and stores monthly payment and total payments 

// Has methods to print out values with nice formatting 

Custom data stored in a Bundle must be Serializable or Parceleable.

Results (Saving State) 

533 


User enters some interest rates to 

get this result 

After entering the data as on the left, user 

rotates the screen. Data is preserved!



More Lifecycle Events 




Overview 


–You can respond to situations other than app being killed and 

app being restarted 

• Situations 

535 


–Another Activity partially obscures Activity 

• Use onPause 

–Activity is no longer visible at all 

• Use onStop 

–A stopped Activity is restarted 

• Use onStart (every time including first) or 

onRestart (every time except first) 

–An Activity is killed for good (no saved state Bundle) 

• Use onDestroy

Lifecycle Summary 

onSaveInstanceState is called 

here 

536 


If state was saved before, 

onRestoreInstanceState is 

called here 

Diagram taken from top of http://developer.android.com/reference/android/app/ 

Activity.html


Wrap-Up 





More Reading 

• JavaDoc: Activity 

–http://developer.android.com/reference/android/app/ 

Activity.html 

• Introductory parts give lots of details 

• Chapters 

538 


–Handling Activity Lifecycle Events and 

–Handling Rotation 

• From The Busy Coder’s Guide to Android Development 

by Mark Murphy. 

– http://commonsware.com/Android/

Summary 

• Save data in onSaveInstanceState 

–Can put individual pieces of data in the Bundle, or can add a 

composite data structure. 

–Custom classes must implement Serializable or Parceleable 

• Load data in onRestoreInstanceState 

or in onCreate 

539 


–Look in Bundle for property of given name 

–For Object types, check for null 

–For number types, check for 0


Network Programming: 

Part I (General Techniques) 








• Part I (this section): general networking 

– Socket basics 

– Requesting Internet permission 

– Example: NIST atomic time 

– Aside: simple String formatting and parsing 

– Example: FTP welcome messages 

– Example: validating URLs with HEAD 

• Part II (next section): HTTP-specific approaches 

– HttpURLConnection 

– HttpClient 

– Examples: Searching Web pages 

– Using JSON 

– Example: remote loan calculations 

– Example: Google translation services 

541 

jeudi 26 janvier 12


Overview 






• Many ways to communicate with a server 

543 


–Socket class 

• Lets you do general-purpose network programming 

– Same as with desktop Java programming 

–HttpURLConnection 

• Simplifies connections to HTTP servers 


–HttpClient 

• Simplest way to download entire content of a URL 

– Not standard in Java SE, but standard in Android 

–JSONObject 

• Simplifies creation and parsing of JSON data 

– Not standard in Java SE, but standard in Android


Socket Basics 





Steps for Talking to Server 

1. Create a Socket object 

Socket client = new Socket("hostname", portNumber); 

2. Create output stream to send data to the Socket 

// Last arg of true means autoflush -- flush stream 

// when println is called 

PrintWriter out = 

new PrintWriter(client.getOutputStream(), true); 

3. Create input stream to read response from server 

545 


BufferedReader in = 

new BufferedReader 

(new InputStreamReader(client.getInputStream()));

Steps for Implementing a Client 

(Continued) 

4. Do I/O with the input and output Streams 

– For the output stream, PrintWriter, use print, println, and printf, similar to 

System.out.print/println/printf 

• The main difference is that you can create PrintWriters for different 

Unicode characters sets, and you can’t with PrintStream (the class 

of System.out). 

– For input stream, BufferedReader, call read to get a single char or an 

array of characters, or call readLine to get a whole line 

• Note that readLine returns null if the connection was terminated (i.e. 

on EOF), but waits otherwise 

– You can use ObjectInputStream and ObjectOutputStream for 

Java-to-Java communication. Very powerful and simple. 

5. Close the socket when done 

client.close(); 

• Also closes the associated input and output streams 

546 

jeudi 26 janvier 12

Exceptions 

• UnknownHostException 

–If host passed to Socket constructor is not known to DNS 

server. 

• Note that you may use an IP address string for the host 

• IOException 

547 


–Timeout 

–Connection refused by server 

–Interruption or other unexpected problem 

• Server closing connection does not cause an error when reading: 

null is returned from readLine

Helper Class: SocketUtils 


–It is common to make BufferedReader and PrintWriter from a 

Socket, so simplify the syntax slightly 


public class SocketUtils { 

} 

548 


public static BufferedReader getReader(Socket s) throws IOException { 

return(new BufferedReader 

(new InputStreamReader(s.getInputStream()))); 

} 

public static PrintWriter getWriter(Socket s) throws IOException { 

// Second argument of true means autoflush. 

return (new PrintWriter(s.getOutputStream(), true)); 

}

Requesting Internet Permission 

• Apps that use internet must say so 

–User will be notified that app wants internet permission, and 

can deny it. Apps that do not request permission will be 

denied access by the Android OS 

• It is possible with effort to circumvent this by launching a hidden 

Web browser that has data embedded in URL 

– See http://dtors.org/2010/08/06/circumventing-android-permissions/ 

• AndroidManifest.xml 

 

 

 

 

… 

 

549 

jeudi 26 janvier 12


Example: 

NIST Time Server 





Time from US National Inst. of 

Standards & Technology (NIST) 


–NIST sponsors several servers with high-precision time 

• The simplest to read is Daytime Protocol (RFC-867), which 

returns the time on the second line of the response to a 

connection. Runs on port 13. 

– See http://www.nist.gov/pml/div688/grp40/its.cfm 

– One popular host name is time-b.nist.gov 

• Approach 

551 


–Make a Socket connection to time-b.nist.gov on port 13 

–Create a BufferedReader (no PrintWriter needed) 

–Read first line of result and ignore it 

–Read second line of result and print it out

Manifest File 


 

 

 

... 

 

552 

jeudi 26 janvier 12

Layout File 

(res/layout/nist_time.xml) 

 

 

 

 

 

553 

jeudi 26 janvier 12

Values Files 


–Defines title, prompts, and button labels for all Activities in 

this section. 


• res/values/colors.xml 

–Defines foreground color for some of the results 






554 




Main Activity 

(NistTimeActivity.java) 

public class NistTimeActivity extends Activity { 

private String mHost = "time-b.nist.gov"; 

private int mPort = 13; 

private TextView mResultDisplay; 

555 





setContentView(R.layout.nist_time); 

mResultDisplay = 

(TextView)findViewById(R.id.time_display); 

}

} 

Main Activity, Continued 

(NistTimeActivity.java) 

556 


public void showTime(View clickedButton) { 

try { 

Socket socket = new Socket(mHost, mPort); 

BufferedReader in = SocketUtils.getReader(socket); 

in.readLine(); // Ignore leading blank line 

String timeResult = in.readLine(); 

mResultDisplay.setText(timeResult); 

socket.close(); 

} catch (UnknownHostException uhe) { 

mResultDisplay.setText("Unknown host: " + mHost); 

uhe.printStackTrace(); // View this in DDMS window 

} catch (IOException ioe) { 

mResultDisplay.setText("IOException: " + ioe); 

ioe.printStackTrace(); // View this in DDMS window 

} 

}

Results 

557 

jeudi 26 janvier 12


Aside: 

String Formatting and 

Parsing 





Formatting and Parsing 

Strategies 


–Simple to connect to a server and create Reader/Writer 

–So, hard parts are formatting request and parsing response 

• Approach 

559 


–Formatting requests 

• Use printf (aka String.format) 

–Parsing response: simplest 

• Use StringTokenizer 

–Parsing response: more powerful 

• Use String.split with regular expressions 

–Parsing response: most powerful 

• Use Pattern and full regex library 

– Not covered in this tutorial

Formatted Output: printf 

• Takes a variable number of arguments 

–System.out.printf("Formatting String", arg1, arg2, …); 

• Advantages 

–Lets you insert values into output without much clumsier 

String concatenation. 

–Lets you control the width of results so things line up 

–Lets you control the number of digits after the decimal point 

in numbers, for consistent-looking output 

• Very similar to C/C++ printf function 

560 


–If you know printf in C/C++, you can probably use Java's 

printf immediately without reading any documentation 

• Although some additions in time formatting and locales 

–Use String.format to get the equivalent of C’s sprintf

Simple Example: printf vs. println 

• General idea 

– Each %s entry in formatting string is replaced by next argument in 

argument list. %n means newline. 

• Example 

public static void printSomeStrings() { 

String firstName = "John"; 

String lastName = "Doe"; 

int numPets = 7; 

String petType = "chickens"; 

System.out.printf("%s %s has %s %s.%n", 

firstName, lastName, numPets, petType); 

System.out.println(firstName + " " + lastName + 

" has " + numPets + " " + 

petType + "."); 

} 

• Result: 

John Doe has 7 chickens. 

John Doe has 7 chickens. 

561 

jeudi 26 janvier 12

Controlling Formatting 

• Different flags 

–%s for strings, %f for floats/doubles, %t for dates, etc. 

• Unlike in C/C++, you can use %s for any type (even nums) 

• Various extra entries can be inserted 

–To control width, number of digits, commas, justification, 

type of date format, and more 

• Complete details 

–printf uses mini-language 

• Complete coverage would take an entire lecture 

• However, basic usage is straightforward 

–For complete coverage, see 

http://download.oracle.com/javase/6/docs/api/java/util/Formatter.html#syntax 

• Most common errors 

– Using + instead of , between arguments (printf uses varargs) 

– Forgetting to add %n at the end if you want a newline (not automatic) 

562 

jeudi 26 janvier 12

Printf Formatting Options 

%s 

%d 

Stands For Options Example 

String. Can output any data 

type. If arg is Object, toString is 

called. 

Decimal. Outputs whole 

number in base 10. Also %x 

and %o for hex and octal. 

%f Floating point. Lets you line 

up decimal point and control 

precision. 

%tx 

563 


Time (or date). %tA for day, 

%tB for month, %tY for year, 

and many more. 

%widths 

Gives min num of chars. 

Spaces added to left if 

needed. 

%widthd %,widthd 

Gives min width; inserts 

commas. 

%width.precisionf 

%,width.precisionf 

width includes comma and 

decimal point. 

Date now = new Date(); 

printf("%8s", "Hi") 

outputs 

" Hi" 

printf("%tA, %tB ,%tY", now, now, now) 

outputs 

"Thursday, November 17, 2005" 

printf("%,9d", 1234) 

outputs 

" 1,234" 

printf("%6.2f", Math.PI) 

outputs 

" 3.14" 

%n Outputs OS-specific end of line (linefeed on Linux/Unix, CR/LF pair on Windows)

Printf Example: Controlling Width 

and Precision 

public class CEO { 

private String name; 

private double salary; // In billions 

} 

564 


public CEO(String name, double salary) { 

this.name = name; 

this.salary = salary; 

} 

public String getName() { return(name); } 

public double getSalary() { return(salary); } 

Note that you cannot make a class with a “main” method in an Android app and run it from Eclipse in the 

usual way (R-click, Run As � Java Application). So, the printf and parsing examples are in a separate 

project called NetworkingSupport. This project also contains the servlet used in the second networking 

lecture.

Printf Example: Controlling Width 

and Precision 

public static void printSomeSalaries() { 

CEO[] softwareCEOs = 

{ new CEO("Steve Jobs", 3.1234), 

new CEO("Scott McNealy", 45.5678), 

new CEO("Jeff Bezos", 567.982323), 

new CEO("Larry Ellison", 6789.0), 

new CEO("Bill Gates", 78901234567890.12)}; 

System.out.println("SALARIES:"); 

for(CEO ceo: softwareCEOs) { 

System.out.printf("%15s: $%,8.2f%n", 

ceo.getName(), ceo.getSalary()); 

}} 

SALARIES: 

Steve Jobs: $ 3.12 

Scott McNealy: $ 45.57 

Jeff Bezos: $ 567.98 

Larry Ellison: $6,789.00 

Bill Gates: $78,901,234,567,890.12 

565 

jeudi 26 janvier 12

Parsing Strings Using 

StringTokenizer 


566 


–Build a tokenizer from an initial string 

–Retrieve tokens one at a time with nextToken 

–You can also see how many tokens are remaining 

(countTokens) or simply test if the number of tokens 

remaining is nonzero (hasMoreTokens) 

StringTokenizer tok 

= new StringTokenizer(input, delimiters); 

while (tok.hasMoreTokens()) { 

doSomethingWith(tok.nextToken()); 

}

StringTokenizer 

• Constructors 

– StringTokenizer(String input, String delimiters) 

– StringTokenizer(String input, String delimiters, 

boolean includeDelimiters) 

– StringTokenizer(String input) 

• Default delimiter set is " \t\n\r\f" (whitespace) 

• Methods 

– nextToken(), nextToken(String delimiters) 

– countTokens() 

– hasMoreTokens() 

• Also see methods in String class 

– split, substring, indexOf, startsWith, endsWith, compareTo, … 

– Java has good support for regular expressions 

567 

jeudi 26 janvier 12

Interactive Tokenizer: Example 

import java.util.StringTokenizer; 

public class TokTest { 

public static void main(String[] args) { 

if (args.length == 2) { 

String input = args[0], delimiters = args[1]; 

StringTokenizer tok 

= new StringTokenizer(input, delimiters); 

while (tok.hasMoreTokens()) { 

System.out.println(tok.nextToken()); 

} 

} else { 

System.out.println 

("Usage: java TokTest string delimiters"); 

} 

} 

} 

568 

jeudi 26 janvier 12

Interactive Tokenizer: Result 

> java TokTest http://www.microsoft.com/~gates/ :/. 

http 

www 

microsoft 

com 

~gates 

> java TokTest "if (tok.hasMoreTokens()) {" "(){. " 

if 

tok 

hasMoreTokens 

569 

jeudi 26 janvier 12

Parsing Strings using the split 

method of String 

• Basic usage 

– String[] tokens = mainString.split(delimiterString); 

• Differences from StringTokenizer 

– Entire string is the delimiter (not one-char delimiters) 

• "foobar".split("ob") returns "fo" and "ar" 

• "foobar".split("bo") returns "foobar" 

– You can use regular expressions in the delimiter 

• ^, $, *, +, ., etc for beginning of String, end of String, 0 or more, 1 or more, 

any one character, etc. 

• See http://download.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html#sum 

– Unless you use "+", an empty string is returned between delimiters 

• "foobar".split("o") returns "f", "", and "bar" 

• "foobar".split("o+") returns "f" and "bar" 

– You can supply second argument to split 

• Giving max splits; any extras go in final string 

570 

jeudi 26 janvier 12

Importance of Regular 

Expressions 


–String.split and other 

methods use regular 

expressions 

–So do many other languages. 

Knowing regex syntax is 

an important part of every 

programmer’s repertoire. 

• Tutorials 

571 


From Randall Munroe and xkcd.com 

– http://download.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html#sum 

– http://download.oracle.com/javase/tutorial/essential/regex/

Interactive Tokenizer: Example 

public class SplitTest { 



String[] tokens = args[0].split(args[1]); 

for(String token: tokens) { 

if (token.length() != 0) { 

System.out.println(token); 

} 

} 

} else { 


("Usage: java SplitTest string delimeters"); 

} 

} 

} 

572 

jeudi 26 janvier 12

Interactive Tokenizer: Result 

> java TokTest http://www.microsoft.com/~gates/ :/. 

http 

www 

microsoft 

com 

~gates 

> java SplitTest http://www.microsoft.com/~gates/ :/. 

http 

www.microsoft.com/~gates/ 

> java SplitTest http://www.microsoft.com/~gates/ [:/.]+ 

http 

www 

microsoft 

com 

~gates 

573 

jeudi 26 janvier 12



Example: 

FTP Welcome Messages 




FTP Server Welcome Messages 


–When you connect to an FTP server, you usually get a 

welcome message. The problem is that it can be a variable 

number of lines long. 

• If multiline, first line should start with "220-" (220 dash) and last 

line should start with "220 " (220 space) 

• Approach 

575 


–Connect to server on port 21 and read first line 

• If it does not start with "220-", print it and exit 

–If first line does start with "220-", read and echo lines until 

you find one that starts with "220 ".

Example Welcome Messages 

• ftp.microsoft.com 

> ftp ftp.microsoft.com 

220 Microsoft FTP Service 

• ftp.oracle.com 

> ftp ftp.oracle.com 

220-*********************************************************************** 

220-Oracle FTP Server 

220- 

220-The use of this FTP server is governed by United States Export Admini- 

220-stration Regulations. Details of the U.S. Commercial Encryption Export 

220-Controls can be found at the Bureau of Industry and Security web site. 

220-All Oracle products are subject to U.S. Export Laws. Diversion contrary 

220-to U.S. law is prohibited. 

... 

220- 

220-**************************************************************************** 

220- 

220 

576 

jeudi 26 janvier 12

Example Welcome Message 

> ftp ftp.ngc.com 

220-*************************************************************************** 

* Access Restricted * 

* The Northrop Grumman computer network is for use, only by authorized * 

* users, and only for authorized purposes. Unauthorized sending, * 

* transmitting, or otherwise disseminating proprietary data or trade * 

* secrets, private company information or classified data is strictly * 

* prohibited. The network and its contents are the exclusive property of * 

* the company. There is no right of privacy on the part of any 

* 

* individual, regarding any information transmitted, stored or received 

* 

* via the network. Employees may access the Northrop Grumman Global * 

* Network only by using tools provided by IT Solutions. Use of other * 

* remote access services is strictly prohibited. Use or access to the 

* 

* network constitutes consent to the company's acceptable use provisions * 

* contained in Corporate Procedure R1, and to the monitoring, storage, * 

* retrieval or disclosure or any information transmitted, stored or * 

* received via the network for any purpose, including employee * 

* discipline, contractual remedies or criminal prosecutions. * 

* Passwords must comply with Corporate policy UO J104. * 

*************************************************************************** 

220 FTP server ready 

577 

jeudi 26 janvier 12

Manifest File 


 

 

 

... 

 

578 

jeudi 26 janvier 12


(res/layout/ftp_message.xml) 

 

 

 

 

 

 

 

 

 

 

 

 

 

579 

jeudi 26 janvier 12


(res/layout-land/ftp_message.xml) 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

580 

jeudi 26 janvier 12

Values Files 



this section. 









581 




Main Activity 

(FtpMessageActivity.java) 

public class FtpMessageActivity extends Activity { 

private EditText mFtpHost; 

private TextView mFtpMessageResult; 

private static final int FTP_PORT = 21; 

582 





setContentView(R.layout.ftp_message); 

mFtpHost = (EditText)findViewById(R.id.ftp_host); 

mFtpMessageResult = 

(TextView)findViewById(R.id.ftp_message_result); 

}



583 


public void showMessage(View clickedButton) { 

String host = mFtpHost.getText().toString(); 

try { 

Socket socket = new Socket(host, FTP_PORT); 


List results = new ArrayList(); 

String line = in.readLine(); 

results.add(line); 

if (line.startsWith("220-")) { 

while((line = in.readLine()) != null) { 

results.add(line); 

if ((line.equals("220") || 

line.startsWith("220 "))) { 

break; 

} 

} 

} 

String output = makeOutputString(results); 

mFtpMessageResult.setText(output); 

socket.close();

} 



584 


} 


mFtpMessageResult.setText("Unknown host: " + host); 



mFtpMessageResult.setText("IOException: " + ioe); 


} 

private String makeOutputString(List results) { 

StringBuilder output = new StringBuilder(); 

for (String s: results) { 

output.append(s + "\n"); 

} 

return(output.toString()); 

}

Results 

585 

jeudi 26 janvier 12



Example: Verifying URLs 

with the HEAD Command 




The HEAD Command 


– Web browsers normally send GET or POST requests 

• Server responds with status line, response headers, blank line, and 

then the document 

– If you only care about status line, send HEAD instead 

• Server responds only with status line and response headers 

• Approach 

– Parse a URL into the host, port (80 if none) and URI 

– Connect to host on port. Send request for URI plus Host request 

header (for servers with virtual hosting) 

– Read status line and see if it is 2xx (good), 3xx (forwarded) or 

anything else (bad). 

• If forwarded, keep reading to find Location header 

• Note 

– Here we use no HTTP-specific classes. Next tutorial section 

covers HttpURLConnection and other HTTP-specific classes. 

587 

jeudi 26 janvier 12

HTTP Request/Response: 

GET 

• Request 

GET /foo/bar.html HTTP/1.1 

Host: ... 

Header2: ... 

... 

HeaderN: 

(Blank Line) 

588 


• Response 

HTTP/1.1 200 OK 

Content-Type: text/html 


... 

HeaderN: ... 

(Blank Line) 

 

 

... 

 

... 

HTTP Request/Response: 

HEAD 

• Request 

HEAD /foo/bar.html HTTP/1.1 

Host: ... 


... 

HeaderN: 

(Blank Line) 

589 


• Response 

HTTP/1.1 200 OK 

Content-Type: text/html 


... 

HeaderN: ...

Using Telnet to Test Server 

Commands 

• Telnet 

–Most people think of telnet as a tool for logging into a remote 

server on default login port (23) 

–But, it is really more general: a tool for connecting to a 

remote server on any port and interactively sending 

commands and looking at results 

• Enabling telnet on Windows 7 or Vista 

590 


–Starting with Windows Vista, telnet is disabled by default 

• To enable it, see http://technet.microsoft.com/ 

en-us/library/cc771275(WS.10).aspx 

• Or Google for “install telnet windows 7” and above page will 

come up #1 

• You may also need to turn on local echo – Unix telnet clients are 

much more convenient

Example: Steve Ballmer’s Home 

Page at Microsoft 

> telnet www.microsoft.com 80 

Trying 207.46.19.254... 

Connected to lb1.www.ms.akadns.net. 

Escape character is '^]'. 

HEAD /presspass/exec/steve/default.aspx HTTP/1.0 

HTTP/1.1 200 OK 

Cache-Control: private 

Content-Length: 182105 

Content-Type: text/html; charset=utf-8 

Server: Microsoft-IIS/7.5 

X-AspNet-Version: 2.0.50727 

VTag: 279105531500000000 

P3P: CP="..." 

X-Powered-By: ASP.NET 

Date: Tue, 02 Aug 2011 17:58:43 GMT 

Connection: keep-alive 

Connection to lb1.www.ms.akadns.net 

closed by foreign host. 

591 


This URI corresponds to the full URL http://www.microsoft.com/ 

presspass/exec/steve/default.aspx, which is the real bio page for 

Steve Ballmer. 

Also, since microsoft.com is using dedicated hosting, I can use the 

simpler HTTP 1.0 HEAD request (with no Host header). The Java 

code will use HTTP 1.1 with the Host header, so that it can also 

handler sites that use virtual (shared) hosting.

Example: Larry Ellison’s Home 

Page at Microsoft 

> telnet www.microsoft.com 80 

Trying 207.46.19.254... 

Connected to lb1.www.ms.akadns.net. 

Escape character is '^]'. 

HEAD /presspass/exec/larry/default.aspx HTTP/1.0 

HTTP/1.1 302 Found 

Content-Length: 293 

Content-Type: text/html; charset=utf-8 

Location: http://www.microsoft.com/library/errorpages/ 

smarterror.aspx?aspxerrorpath=http%3a%2f 

%2f207.46.21.164%2fpresspass%2fexec%2flarry%2fdefault.aspx 

... 

Date: Tue, 02 Aug 2011 18:06:11 GMT 

Connection: keep-alive 

Connection to lb1.www.ms.akadns.net closed by foreign host. 

592 


This corresponds to http://www.microsoft.com/presspass/exec/larry/ 

default.aspx, which is a nonexistent page. The page they forward to 

should return 404 to prevent indexing by search engines.

Manifest File 


 

 

 

... 

 

593 

jeudi 26 janvier 12


(res/layout/url_checker.xml) 

 

 

 

 

 

 

 

 

 

 

 

 

 

594 

jeudi 26 janvier 12


(res/layout-land/url_checker.xml) 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

595 

jeudi 26 janvier 12

Values Files 



this section. 









596 




Main Activity 

(UrlCheckerActivity.java) 

public class UrlCheckerActivity extends Activity { 

private EditText mUrlToTest; 

private TextView mUrlMessageResult; 

597 





setContentView(R.layout.url_checker); 

mUrlToTest = 

(EditText)findViewById(R.id.url_to_test); 

mUrlMessageResult = 

(TextView)findViewById 

(R.id.url_validation_result); 

}



598 


public void checkUrl(View clickedButton) { 

String url = mUrlToTest.getText().toString(); 

UrlParser parser = new UrlParser(url); 

String host = parser.getHost(); 

int port = parser.getPort(); 

String uri = parser.getUri(); 

try { 

Socket socket = new Socket(host, port); 

PrintWriter out = SocketUtils.getWriter(socket); 


out.printf("HEAD %s HTTP/1.1\r\n", uri); 

out.printf("Host: %s\r\n", host); 

out.printf("Connection: close\r\n\r\n"); 

String serverResult = in.readLine(); 

String info = statusInfo(serverResult, in); 

mUrlMessageResult.setText(info); 

socket.close();



599 


} 


mUrlMessageResult.setText("Unknown host: " + host); 



mUrlMessageResult.setText("IOException: " + ioe); 


}



600 


private String statusInfo(String serverResult, BufferedReader in) 

throws IOException { 

StatusLineParser statusLine = new StatusLineParser(serverResult); 

String result; 

if (statusLine.isGood()) { 

result = String.format("Good URL: %s -- %s", 

statusLine.getStatusCode(), 

statusLine.getMessage()); 

} else if (statusLine.isForwarded()) { 

result = String.format("URL forwarded to %s", 

location(in)); 

} else { 

result = String.format("Bad URL: %s -- %s", 

statusLine.getStatusCode(), 

statusLine.getMessage()); 

} 

return(result); 

}



601 


private String location(BufferedReader in) throws IOException { 

String line; 

while((line = in.readLine()) != null) { 

if (line.toUpperCase().startsWith("LOCATION")) { 

String[] results = line.split("\\s+", 2); 

return(results[1]); 

} 

} 

return("(Unknown Location)"); 

}

Helper Classes 

• StatusLineParser 

–Reads status line and breaks it into three parts: HTTP version, 

status code, and message 

• Also isGood (status code in the 200’s), isForwarded (301/302) 

and isBad (anything else) methods 

• UrlParser 

602 


–Breaks a URL like http://host:port/path into the host, port, and 

path parts. Uses 80 if no port specified. 

–Note that the builtin URL class already does this. See next 

lecture. But Android has no builtin support for protocols other 

than HTTP, so learning to do it yourself is important.

Results 

603 

jeudi 26 janvier 12


Wrap-Up 





More Reading 

• JavaDoc 

– Socket 

• http://developer.android.com/reference/java/net/Socket.html 

– Pattern (gives regular expression details) 

• http://developer.android.com/reference/java/util/regex/Pattern.html 

• Tutorial: Networking 

– http://download.oracle.com/javase/tutorial/networking/ 

• Not Android specific, but still very good networking coverage 

• Chapters 

– Networking and Web Services 

• From Android in Action by Ableson et al 

– Communicating via the Internet 


by Mark Murphy (http://commonsware.com/Android/) 

605 

jeudi 26 janvier 12

Summary 

• Basics 

– Socket socket = new Socket(host, port); 

– PrintWriter out = SocketUtils.getWriter(socket); 

– BufferedReader in = SocketUtils.getReader(socket); 

• Slightly longer if you don’t use SocketUtils 

• Catch UnknownHostException and IOException 

– Ask for Internet permission in AndroidManifest.xml 

• Formatting and parsing 

– Format request: printf 

– Handle response 

• Read lines with readLine. Remember it blocks and waits for either 

end-of-line (String) or closed connection (null). 

• Parse the line with StringTokenizer or String.split 

606 


– To use the split method, learn regular expressions



Network Programming: 

Part II (HTTP-Specific Techniques) 







• Part I (previous section): general networking 

– Socket basics 

– Requesting Internet permission 

– Example: NIST atomic time 

– Aside: simple String formatting and parsing 

– Example: FTP welcome messages 

– Example: validating URLs with HEAD 

• Part II (this section): HTTP-specific approaches 

– HttpURLConnection 

– HttpClient 

– Examples: Searching Web pages 

– Using JSON 

– Example: remote loan calculations 

– Example: Google translation services 

608 

jeudi 26 janvier 12


Overview 






• Many ways to communicate with a server 

610 


–Socket class 

• Lets you do general-purpose network programming 



• Simplifies connections to HTTP servers 


–HttpClient 

• Simplest way to download entire content of a URL 

– Not standard in Java SE, but standard in Android 

–JSONObject 

• Simplifies creation and parsing of JSON data 

– Not standard in Java SE, but standard in Android


HttpURLConnection 





URL and HttpURLConnection: 

Overview 

• URL 

– The URL class can parse a URL and extract its components 

(protocol, host, port, URI, etc.) 

– You can use openConnection to get a stream to the URL 

• HttpURLConnection 

– If the URL’s protocol is HTTP, cast the result of openConnection 

to HttpURLConnection 

• Lets you read the status code 

612 


– 200, 301, 404, etc. 

• Lets you set request headers 

– Accept, Referer, User-Agent, etc. 

• Lets you read response headers 

– Content-Type, Location, etc. 

• Special case for cookies 

– Use CookieManager instead of raw headers

URL: Details 

• openConnection 

–Establishes connection to server. 

• Cast result to HttpURLConnection for more control 

• Uses GET by default. To use POST, call setDoOutput(true) and 

send data via openOutputStream 

• openInputStream 

–Gets a Stream for reading data. Wrap in InputStreamReader 

(usually buffered) to use readLine. 

• getProtocol, getHost, getPort, getFile, getRef 

613 


–Returns the different components of the URL. 

• The port is -1 if none specified, so you can distinguish an omitted 

port from an explicit 80.

Simple URL Methods: Example 

import java.net.*; 

public class UrlTest { 



try { 

URL url = new URL(args[0]); 


("URL: " + url.toExternalForm() + "\n" + 

" File: " + url.getFile() + "\n" + 

" Host: " + url.getHost() + "\n" + 

" Port: " + url.getPort() + "\n" + 

" Protocol: " + url.getProtocol() + "\n" + 

" Reference: " + url.getRef()); 

} catch(MalformedURLException mue) { 

System.out.println("Bad URL."); 

} 

} else 

System.out.println("Usage: UrlTest "); 

} 

} 

614 

jeudi 26 janvier 12

Simple URL Methods: Results 

> java UrlTest http://www.irs.gov/mission/#squeezing-them-dry 

URL: http://www.irs.gov/mission/#squeezing-them-dry 

File: /mission/ 

Host: www.irs.gov 

Port: -1 

Protocol: http 

Reference: squeezing-them-dry 

615 


What month do you think it was when I first wrote this example?

HttpURLConnection: Details 

• Getting a connection from a URL 

URL url = new URL("http://…"); 

HttpURLConnection urlConnection = 

(HttpURLConnection)url.openConnection(); 

• Reading data 


new BufferedReader(new InputStreamReader 

(urlConnection.getInputStream())); 

while ((line = in.readLine()) != null) { 

doSomethingWith(line); 

} 

• Other methods 

616 


–disconnect, getResponseCode, getHeaderField 

• Call disconnect when done



Example: Searching Web 

Pages for Keywords 

(Version 1) 




URL Searcher 


–Print out all lines in a given URL that contain keyword 

• Approach 

618 


–Read URL and keyword from user 

–Call theUrl.openConnection and cast result to 

HttpURLConnection 

–Attach BufferedReader to the HttpURLConnection 

–Read one line at a time (until null), checking if the line 

contains the keyword 

–Catch MalformedURLException and IOException 

–Call disconnect() when done

Manifest File 


 

 

 

... 

 

619 

jeudi 26 janvier 12

Layout File (res/layout/ 

url_searcher.xml) 

 

 

 

 

... 

 

 

 

 

 

 

 

 

 

 

 

620 

jeudi 26 janvier 12

Values Files 



this section. 









621 




Main Activity 

(UrlSearcher1Activity.java) 

public class UrlSearcher1Activity extends Activity { 

protected EditText mUrlToSearch, mSearchString; 

protected TextView mUrlMessageResult; 

protected float mResultTextSize, mErrorTextSize; 

622 





setContentView(R.layout.url_searcher); 

mUrlToSearch = (EditText)findViewById(R.id.url_to_search); 

mSearchString = (EditText)findViewById(R.id.search_string); 

mUrlMessageResult = 

(TextView)findViewById(R.id.url_search_result); 


mResultTextSize = 

resources.getDimension(R.dimen.url_search_results_size); 

mErrorTextSize = 

resources.getDimension(R.dimen.url_search_error_size); 

} 

Note the protected fields and (next slides) methods – next example will extend this class and share much of the code.



623 


public void searchInUrl(View clickedButton) { 

String urlString = 

mUrlToSearch.getText().toString(); 

String searchString = 

mSearchString.getText().toString(); 

showResults(urlString, searchString); 

} 

This is the method called by the Button. Next example will inherit it unchanged.



624 


protected void showResults(String urlString, String searchString) { 

HttpURLConnection urlConnection = null; 

try { 

URL url = new URL(urlString); 

urlConnection = (HttpURLConnection)url.openConnection(); 


new BufferedReader 

(new InputStreamReader(urlConnection.getInputStream())); 

String line; 

StringBuilder matches = new StringBuilder(""); 

int lineNum = 0; 

int numMatches = 0; 

while ((line = in.readLine()) != null) { 

lineNum++; 

if(line.contains(searchString)) { 

numMatches++; 

matches.append(makeMatch(line, lineNum)); 

} 

} 

displayResults(matches, numMatches); 

This is the method that is overridden in the next example.



625 


} 

} catch (MalformedURLException mue) { 

showError("Bad URL: " + urlString); 

mue.printStackTrace(); // View this in DDMS window 


showError("Error in connection: " + ioe); 


} finally { 

if (urlConnection != null) { 

urlConnection.disconnect(); 

} 

} 

This is a continuation of the showResults method started on previous slide.



626 


protected String makeMatch(String text, int lineNum) { 

return(String.format("LINE %s: %s%n", lineNum, text)); 

} 

protected void displayResults(StringBuilder matches, 

int numMatches) { 

if (numMatches > 0) { 

showMatches(matches, numMatches); 

} else { 

showError("No matches"); 

} 

}

} 



627 


protected void showMatches(StringBuilder matches, 

int numMatches) { 

String introMessage = 

String.format("FOUND %s MATCHES:%n%n", 

numMatches); 

matches.insert(0, introMessage); 

mUrlMessageResult.setTextSize(mResultTextSize); 

mUrlMessageResult.setText(matches); 

} 

protected void showError(String text) { 

mUrlMessageResult.setTextSize(mErrorTextSize); 

mUrlMessageResult.setText("\n\n" + text); 

}

Results 

628 

jeudi 26 janvier 12


HttpClient 





HttpClient 


–A popular class from the Apache HttpComponents suite that is 

bundled with Android. 

• Minor problem: Android does not document precisely which 

version it uses, so hard to use Apache tutorials 

• Capabilities 

630 


–Simple way to read an entire URL (via GET) into String 

–Moderately simple way to send POST parameters, then read 

entire result into a String 

–Many, many other capabilities 

• But only the simple reading of content is shown in this tutorial. 

For other capabilities, see http://hc.apache.org/httpclient-3.x/ 

tutorial.html

HttpClient: Reading Result of GET 

Request 

• Make a default client 

–HttpClient client = new DefaultHttpClient(); 

• Make an HttpGet with address 

–HttpGet httpGet = new HttpGet(address); 

• Make a String ResponseHandler 

–ResponseHandler handler = 

new BasicResponseHandler(); 

• Call client.execute 

631 


–String content = client.execute(httpGet, handler);

HttpClient: Reading Result of 

POST Request 

• Make a default client 

HttpClient client = new DefaultHttpClient(); 

• Make an HttpPost with address 

HttpPost httpPost = new HttpPost(address); 

• Make a List of name/value pairs 

List params = new ArrayList(); 

params.add(new BasicNameValuePair(paramName1, paramValue1)); 

params.add(…); // More names and values. NOT URL-encoded 

• Attach POST data 

UrlEncodedFormEntity entity = new UrlEncodedFormEntity(params, "UTF-8"); 

httpPost.setEntity(entity); 

• Make a String ResponseHandler 

ResponseHandler handler = new BasicResponseHandler(); 

• Call client.execute 

String content = client.execute(httpPost, handler); 

632 

jeudi 26 janvier 12

HttpUtils 


–A class developed for this tutorial that wraps up some simple 

HttpClient functionality 

• Static methods 

633 


–urlContent(String address) 

• Returns a String containing entire content of address 

• Uses GET. If you want query data, URL encode it and attach it to 

the end of URL after question mark 

–urlContentPost(String address, 

String ... paramNamesAndValues) 

• Returns a String containing entire content of address 

• Uses POST. All args after the first are alternating parameter 

names and unencoded parameter values.

HttpUtils 

634 


public static String urlContent(String address) 

throws IOException, ClientProtocolException { 


HttpGet httpGet = new HttpGet(address); 

ResponseHandler handler = 

new BasicResponseHandler(); 

return(client.execute(httpGet, handler)); 

}

HttpUtils, Continued 

635 


public static String urlContentPost(String address, 

String ... paramNamesAndValues) 

throws IOException, ClientProtocolException { 


HttpPost httpPost = new HttpPost(address); 

List params = new ArrayList(); 

for(int i=0; i



Example: Searching Web 

Pages for Keywords 

(Version 2) 




URL Searcher 


–Redo the previous example, but read URL content with 

HttpClient instead of HttpURLConnection 

• Approach 

637 


–Read URL and keyword from user 

–Call HttpUtils.urlContent(address) to get entire content of 

address as a single String 

–Use String.split to split String on CR or LF 

–Test each array entry to see if it contains keyword 

–Reuse most of the code from the previous example

XML Files 

• AndroidManifest.xml 

–Requests Internet permission as shown previously. Also 

declares the new Activity. 

• res/layout/url_searcher.xml 

–Reuses previous layout file with no changes 

• Values files 

638 


–Reuses previous files with no changes 

• strings.xml 

• colors.xml 

• dimens.xml

Main Activity 


public class UrlSearcher2Activity extends UrlSearcher1Activity { 


protected void showResults(String urlString, 

String searchString) { 

try { 

String urlBody = HttpUtils.urlContent(urlString); 

String[] lines = urlBody.split("[\\n\\r]+"); 

StringBuilder matches = new StringBuilder(""); 

int lineNum = 0; 

int numMatches = 0; 

for (String line: lines) { 

lineNum++; 

if(line.contains(searchString)) { 

numMatches++; 

matches.append(makeMatch(line, lineNum)); 

} 

} 

displayResults(matches, numMatches); 

639 


All methods except showResults are inherited from previous class.

} 



640 


} 

} catch (ClientProtocolException cpe) { 

showError("Bad URL: " + urlString); 

cpe.printStackTrace(); // View this in DDMS window 


showError("Error in connection: " + ioe); 


}

Results 

641 


Identical to previous example.


Aside: JSON Format 





JSON (JavaScript Object Notation) 


–A simple textual representation of (JavaScript) objects 

• Called “object literals” or “anonymous objects” 

–Main applications in JavaScript 

• One-time-use objects (rather than reusable classes) 

• Objects received via strings 

• Directly in JavaScript 

– var someObject = { property1: value1, 

property2: value2, 

... }; 

• Widely used in other languages 

643 


–Lightweight alternative to XML 

–Android has a builtin class (JSONObject) that will both build 

and parse strings representing JSON

JSON: Example in JavaScript 

var person = 

{ firstName: 'Brendan', 

lastName: 'Eich', 

bestFriend: { firstName: 'Chris', 

lastName: 'Wilson' }, 

greeting: function() { 

return("Hi, I am " + this.firstName + 

" " + this.lastName + "."); 

} 

}; 

644 

jeudi 26 janvier 12

Strict JSON 

• Object literals in JavaScript 

–Any way you would type a data structure into JavaScript. 

– { firstName: 'Larry', lastName: 'Page'} 

• Strict JSON according to json.org 

–Subset of JavaScript where: 

• Object property names must be in double quotes 

• Strings are represented with double quotes only (not single 

quotes) 

– { "firstName": "Larry", "lastName": "Page"} 

–This is what Android’s JSONObject supports 

• MIME type for JSON from server 

645 


–RFC 4627 says JSON should have "application/json" type 

–No known libraries enforce this

Popular Web Services that Send 

JSON Data 

• Google APIs 

– Search, translate, data, and many more 

• http://code.google.com/apis/customsearch/v1/overview.html 

• Yahoo APIs 

– Search, travel, answers 

• http://developer.yahoo.com/ 

• Twitter APIs 

– https://dev.twitter.com/ 

• GeoNames 

– http://www.geonames.org/export/web-services.html 

• Flickr 

– http://www.flickr.com/services/api/ 

• Thousands of others 

– See list here 

• http://www.programmableweb.com/apis/directory/1?format=JSON 

646 

jeudi 26 janvier 12


The JSONObject Class 





JSONObject 


–A popular JSON-in-Java library from json.org that is bundled 

with Android. 

• Major problem: Android does not document precisely which 

version it uses, and the version it does use is long-obsolete and 

lacks JSON-from-bean capability 

• Capabilities 

648 


–Builds a JSONObject 

• From String, Map, or bean 

–Lets you extract data from JSONObject 

• getString(name), getDouble(name), etc 

–Lets you output string representing a JSONObject 

• toString

Building a JSONObject 

• Constructors 

649 


–new JSONObject(jsonString) 

• Reads a JSON string and builds JSONObject from it. 

– This is most important constructor for use directly on Android, since main 

Android use of JSON is handling JSON from Web services 

–new JSONObject(nameValueMap) 

• Takes a Map and builds JSON from it. Used on Android if you 

want to send JSON to a Web service 

–new JSONObject(bean) [not in Android version!] 

• Takes a bean and builds JSON based on bean properties. 

Cannot use directly on Android, but very useful on server that 

sends JSON to Android 

– If Android had supported this version, would have been much better way to 

send JSON to a Web service

Extracting Data From a 

JSONObject 

• Accessors 

650 


–get(propertyName) 

• Returns Object associated with name 

–getString(propertyName) 

• Returns String associated with name. Works for any type (if 

Object, uses its toString method) 

–getDouble(propertyName) 

• Returns double associated with name. Throws JSONException if 

value cannot be converted to double. 

–getBlah(propertyName) 

• getInt, getBoolean, etc. Similar in spirit to getDouble. 

–getJSONArray(propertyName) 

• Returns JSONArray (not native Java array!) associated with 

name

Other Capabilities 

• toString 

–Builds strict-JSON string from JSONObject 

• The JSONArray class 

651 


–Represents an array of JSON. 

–Although it can be used to send data from Android, it is 

usually used for received data. 

• { "names": ["larry", "curly", "moe"], 

"primes": [2, 3, 5, 7, 11] }


Using JSONObject 

on Server 





Steps for Servlet Outputting 

JSON (for Android Use) 

• Usual tasks 

– response.setContentType("application/json"); 

– PrintWriter out = response.getWriter 

– Call normal business logic code to get bean, array, or Map 

• New tasks 

653 


– Turn Java object into JSONObject 

• JSONObject result = new JSONObject(bean); 

• JSONArray result = new JSONArray(arrayOfBeans, false); 

• JSONObject result = new JSONObject(map); 

– Output JSONObject with print 

• out.print(result); 

– Automatically calls toString, which does the real JSONification

JSONObject’s Algorithm for 

JSONifying a Java Object 

• Find the bean properties 

–E.g., Name class has getFirstName, and getLastName 

methods, so properties are firstName and lastName 

• Call the associated accessor methods 

–Call each of getFirstName and getLastName on object 

• Build JSON representation 

–JavaScript property names are bean property names 

–Values are results of getter methods 

• Mini Example 

654 


–toString of a JSONObject representing a Name 

• Java: make new Name("John", "Resig"). 

Pass to JSONObject, then call print (which uses toString) 

• Result: { "firstName": "John", "lastName": "Resig"}

Finding Bean Property Name 

Based on Method Name 

• Usual rule 

–Drop the word “get” and change the next letter to lowercase. 

Instance variable name is irrelevant. 

• Method name: getUserFirstName 

• Property name: userFirstName 

• Exception 1: boolean properties 

–If getter returns boolean or Boolean 

• Method name: getPrime or isPrime 

• Property name: prime 

• Exception 2: consecutive uppercase letters 

655 


–If two uppercase letters in a row after “get” 

• Method name: getURL 

• Property name: URL (not uRL)

Bean Properties: Examples 

Method Name Property Name Example JSON Output 

getFirstName firstName { "firstName": "Joe", … } 

isExecutive 

(boolean property) 

656 


getExecutive 

(boolean property) 

executive { "executive": true, … } 

executive { "executive": true, … } 

getZIP ZIP { "ZIP": "12345", … } 

Note 1: property name does not exist anywhere in your code. It is just a shortcut for the method name. 

Note 2: property name is derived only from method name. Instance variable name is irrelevant.

Steps for Using JSON Utilities: 

Sample Servlet Code 

public void doPost(HttpServletRequest request, 

HttpServletResponse response) 

throws ServletException, IOException { 

response.setContentType("application/json"); 

PrintWriter out = response.getWriter(); 

SomeBean javaResult = callSomeBusinessLogic(…); 

JSONObject jsonResult = 

new JSONObject(javaResult); 

out.print(jsonResult); 

} 

657 


Lines in red are the only ones that typically change 

from application to application. Other lines stay exactly as is. 

Calling print automatically calls toString behind the scenes

Drawbacks of JSONification 

• Sends state, not behavior, of object 

–So, properties that are derived from other properties will be 

inconsistent on client if other properties are changed 

• Example: Java “Circle” class 

–getRadius 

• Returns instance variable 

–getArea 

• Returns Math.PI*radius*radius 

• JSONified instance 

658 


–Example 

• Make new Circle(10). Pass to JSONObject, call toString 

• Result: { "radius": 10.0, "area": 314.15927…} 

–Problem 

• If client-side code changes radius, area doesn’t match

JSONObject from Bean: Example 

Code 

public class CityTest1 { 


City sf = CityUtils.getCity("San Francisco"); 

JSONObject sfJSON = new JSONObject(sf); 

System.out.println("JSON version of SF is:\n" + 

sfJSON); 

} 

} 

659 


City is a simple class with a bunch of getter methods 

(getTime, getName, getPopulation, etc.) 

Note: toString is automatically called when you print an Object in Java. It is the 

toString method of JSONObject that builds the JSON representation.

JSONObject from Bean: Example 

Result 

JSON version of SF is: 

{"time": "06:00:55 AM", 

"name": "San Francisco", 

"timeZone": -3, 

"pop": 744041, 

"population": " 744,041"} 

660 


(White space added for readability)



Example: 

Remote Loan Calculator 




JSON-Based Loan Calculator 

Service 


– Make servlet for doing loan calculations 

• Input: JSON object with amount, period, and interest rate 

• Output: JSON object with inputs plus monthly payment and total 

payments 

• Approach 

– Server 

• Read parameter and pass to JSONObject constructor 

• Extract values with getDouble and getLong 

• Use same PaymentInfo class as in several previous examples 

• Turn PaymentInfo into JSON via JSONObject 

– Client (Android) 

• Build Map and turn into JSONObject, send to server 

• Read String, turn into JSONObject 

• Extract info with getString 

662 

jeudi 26 janvier 12

Servlet 

@WebServlet("/loan-calculator") 

public class LoanCalculator extends HttpServlet { 


public void doGet(HttpServletRequest request, HttpServletResponse response) 


String inputString = request.getParameter("loanInputs"); 

double loanAmount = 200000; 

double annualInterestRateInPercent = 5.5; 

long loanPeriodInMonths = 360; 

try { 

JSONObject inputValues = new JSONObject(inputString); 

loanAmount = inputValues.getDouble("amount"); 

annualInterestRateInPercent = inputValues.getDouble("rate"); 

loanPeriodInMonths = inputValues.getLong("months"); 

} catch (Exception e) { // NullPointerException & JSONException 

// Use default values assigned before the try block 

} 

PaymentInfo info = new PaymentInfo(loanAmount, 

annualInterestRateInPercent, 

loanPeriodInMonths); 

PrintWriter out = response.getWriter(); 

out.println(new JSONObject(info)); 

} 

663 


If you are unfamiliar with servlets, see extensive tutorial series 

at http://www.coreservlets.com/

Servlet, Continued 

664 



public void doPost(HttpServletRequest request, 

HttpServletResponse response) 


doGet(request, response); 

} 

Makes the most sense to send the data via POST. However, it also supports GET to simplify interactive testing by editing the browser line. 

This app is installed on apps.coreservlets.com, so URL is http://apps.coreservlets.com/NetworkingSupport/loan-calculator 

You can experiment interactively by calling 

http://apps.coreservlets.com/NetworkingSupport/loan-calculator?loanInputs={amount: 200000, rate: 6.5, months: 180} 

The tutorial Web site has the servlet code as well as the Android code, so you can install the servlet on a local Java server (requires Tomcat 7 

or equivalent). However, note that the Android emulator does not understand localhost as a host name, since it acts like independent device. 

So, you must use real domain name or IP address.

Android Activity 


private EditText mBaseUrl, mLoanAmount, mInterestRate, mLoanPeriod; 

private TextView mMontlyPaymentResult, mTotalPaymentsResult; 

665 





setContentView(R.layout.loan_calculator); 

mBaseUrl = (EditText)findViewById(R.id.base_url); 

mLoanAmount = (EditText)findViewById(R.id.loan_amount); 

mInterestRate = (EditText)findViewById(R.id.interest_rate); 

mLoanPeriod = (EditText)findViewById(R.id.loan_period); 

mMontlyPaymentResult = 

(TextView)findViewById(R.id.monthly_payment_result); 

mTotalPaymentsResult = 

(TextView)findViewById(R.id.total_payments_result); 

}

Android Activity, Continued 

666 


public void showLoanPayments(View clickedButton) { 

String baseUrl = mBaseUrl.getText().toString(); 

String loanAmount = mLoanAmount.getText().toString(); 

String interestRate = mInterestRate.getText().toString(); 

String loanPeriod = mLoanPeriod.getText().toString(); 

LoanInputs inputs = 

new LoanInputs(loanAmount, interestRate, loanPeriod); 

JSONObject inputsJson = new JSONObject(inputs.getInputMap()); 

try { 

String jsonString = 

HttpUtils.urlContentPost(baseUrl, "loanInputs", 

inputsJson.toString()); 

JSONObject jsonResult = new JSONObject(jsonString); 

mMontlyPaymentResult.setText 

(jsonResult.getString("formattedMonthlyPayment")); 

mTotalPaymentsResult.setText 

(jsonResult.getString("formattedTotalPayments")); 

mLoanAmount.setText 

(jsonResult.getString("loanAmount")); 

mInterestRate.setText 

(jsonResult.getString("annualInterestRateInPercent")); 

mLoanPeriod.setText 

(jsonResult.getString("loanPeriodInMonths"));

Helper Class 

public class LoanInputs { 

private Map mInputMap; 

} 

667 


public LoanInputs(String amount, String rate, 

String months) { 

mInputMap = new HashMap(); 

mInputMap.put("amount", amount); 

mInputMap.put("rate", rate); 

mInputMap.put("months", months); 

} 

public Map getInputMap() { 

return(mInputMap); 

}

Results 

668 


http://apps.coreservlets.com/NetworkingSupport/loan-calculator


Example: Google 

Translation Services 





Double Translate App 


– The Google Translate services has a JSON-based API 

– http://code.google.com/apis/language/translate/v2/using_rest.html 

• Can look up all the supported languages 

• Can translate from any supported language into any other 

– Translate from English to foreign and then back to English to see 

how well the translation works 

• Very good for literal text with simple grammar. 

• Approach 

– Get JSONArray representing supported lanuages. 

• Put in Spinner 

– Get JSONObject representing intermediate translation 

• Send back to server to get final translation 

– Only selected code will be shown here. Full code online. 

670 

jeudi 26 janvier 12

Main Activity 

public class DoubleTranslateActivity extends Activity { 

private EditText mText; 

private Spinner mLanguageChoices; 

private TextView mIntermediateResult, mFinalResult; 

private String apiKey = "..."; 

671 


The translate API requires you to apply for 

a free API key and send the key with every 

request.


672 






mText = (EditText)findViewById(R.id.text); 

mLanguageChoices = (Spinner)findViewById(R.id.language_choices); 

List supportedLanguages = 

TranslateUtils.supportedLanguages(apiKey); 

ArrayAdapter spinner2Adapter = 



supportedLanguages); 

spinner2Adapter.setDropDownViewResource 


mLanguageChoices.setAdapter(spinner2Adapter); 

mIntermediateResult = (TextView)findViewById(R.id.intermediate_result); 

mFinalResult = (TextView)findViewById(R.id.final_result); 

}


673 


public void doubleTranslate(View clickedButton) { 

String sourceLanguageCode = "en"; 

Language targetLanguage = 

(Language)mLanguageChoices.getSelectedItem(); 

String targetLanguageCode = targetLanguage.getCode(); 

String textToTranslate = mText.getText().toString(); 

Translator translator = 

new Translator(apiKey, sourceLanguageCode, 

targetLanguageCode, textToTranslate); 

String firstTranslation = translator.getFirstTranslation(); 

mIntermediateResult.setText(firstTranslation); 

String secondTranslation = 

translator.getSecondTranslation(); 

mFinalResult.setText(secondTranslation); 

}

Key Helper Class 

(TranslationUtils) 

public static String translationString 

(String apiKey, String sourceLanguage, 

String targetLanguage, String textToTranslate) { 

try { 

String jsonString = translationJson(apiKey, sourceLanguage, 

targetLanguage, textToTranslate); 

JSONObject jsonObject = new JSONObject(jsonString); 

String text = 

jsonObject.getJSONObject("data").getJSONArray("translations") 

.getJSONObject(0).getString("translatedText"); 

return(text); 

} catch(HttpResponseException hre) { 

int errorCode = hre.getStatusCode(); 

if (errorCode == 403) { // 403 is "Forbidden" 

return(ERROR_FORBIDDEN); 

} else { // Probably 400, "Bad Request" 

return(ERROR_BAD_REQUEST); 

} 

} catch(IOException ioe) { 

return(ERROR_BAD_CONNECTION); 

} catch(JSONException jse) { 

return(ERROR_JSON_PROBLEM); 

} 

} 

674 

jeudi 26 janvier 12

Results: Very Simple Text 

675 

jeudi 26 janvier 12

Results: Medium-Difficulty Text 

676 

jeudi 26 janvier 12

Results: Deliberately-Tricky Text 

677 


The proper interpretation is “old people crew (work on) the boat”. This is an 

example of a garden-path sentence and is taken from http:// 

en.wikipedia.org/wiki/Garden_path_sentence

Results: More Deliberately-Tricky 

Text 

678 


The proper interpretation is “baby deer die when hunters (who are in the 

burning forest) shoot at them”.


Wrap-Up 





More Reading 

• JavaDoc 


• http://developer.android.com/reference/java/net/ 

HttpURLConnection.html 

• HttpClient Tutorial 

–http://hc.apache.org/httpclient-3.x/tutorial.html 

• JSON Tutorials 

680 


–http://json.org/ 

–http://www.webmonkey.com/2010/02/ 

get_started_with_json/ 

–http://www.hunlock.com/blogs/ 

Mastering_JSON_(_JavaScript_Object_Notation_)

Summary 

• Read individual lines from a URL 

–Use HttpURLConnection 

• Read an entire URL as a String 

–Use HttpClient 

• Particularly useful if result is JSON 

• JSON 

–Simple format widely used in Ajax and Web services 

• JSONObject 

681 


–Converts string into JSON 

–Outputs JSON string 

• But builtin Android version lacks most important method, for 

building JSON string from a bean


Multithreaded Programming 

Part I: General Techniques 








• Why threads? 

• Basic approach 

–Make a task list with Executors.newFixedThreadPool 

–Add tasks to list with taskList.execute(someRunnable) 

• Three variations on the theme 

–Separate classes that implement Runnable 

–Main Activity implements Runnable 

–Inner classes that implement Runnable 

• Related topics 

683 


–Race conditions and synchronization 

–Helpful Thread-related methods 

–Advanced topics in concurrency

684 


Overview 





Motivation for Concurrent 

Programming 

• Pros 

–Advantages even on single-processor systems 

• Efficiency 

– Downloading image files 

• Convenience 

– A clock icon 

• Responsiveness 

– If you block the main thread, event handlers will not respond 

–Some devices have multiple cpus or cores 

• Find out via Runtime.getRuntime().availableProcessors() 

• Cons 

685 


–Significantly harder to debug and maintain than single- 

threaded apps

Steps for 

Concurrent Programming 

• First, make a task list 

ExecutorService taskList = 

Executors.newFixedThreadPool(poolSize); 

• The poolSize is the maximum number of simultaneous threads. For 

many apps, it is higher than the number of tasks, so each task has a 

separate thread. 

• There are other types of thread pools, but this is simplest 

• Second, add tasks to the list (three options) 

– Make a separate class that implements Runnable. 

• Make instances of this class and start threading via 

taskList.execute(new MySeparateRunnableClass(…)) 

– Have your existing class implement Runnable. 

• Start threading via taskList.execute(this) 

– Use an inner class. 

• taskList.execute(new MyInnerRunnableClass(…)) 

686 

jeudi 26 janvier 12

687 



Approach One: Separate 

Classes that Implement 

Runnable 




Thread Mechanism One: 

Separate Runnable Class 

• Make class that implements Runnable 

–No import statements needed: Runnable is in java.lang 

• Put actions to be performed in run method 

–public class MyRunnableClass implements Runnable { 

} 

public void run() { … } 

• Create instance of your class 

–Or lots of instances if you want lots of threads 

• Pass instance to ExecutorService.execute 

688 


–taskList.execute(new MyRunnableClass(…)); 

• The number of simultaneous threads won’t exceed the maximum 

size of the pool.

Separate Runnable Class: 

Template Code 

689 


public class MainClass extends Activity { 

... 

public void startSomeThreads() { 

int poolSize = ...; 



for(int i=0; i

Thread Mechanism One: Example 

public class ThreadingBasicsActivity extends Activity { 




setContentView(R.layout.threading_basics); 

} 

} 

690 


public void separateClass(View clickedButton) { 


Executors.newFixedThreadPool(50); 

taskList.execute(new SeparateCounter(6)); 



} 

This method is associated with 

a Button via the 


layout file.

Thread Mechanism One: Example 

(Continued) 

public class SeparateCounter implements Runnable { 

private final int mLoopLimit; 

} 

691 


public SeparateCounter(int loopLimit) { 

this.mLoopLimit = loopLimit; 

} 

public void run() { 

for (int i = 0; i < mLoopLimit; i++) { 

String threadName = 

Thread.currentThread().getName(); 

System.out.printf("%s: %s%n", threadName, i); 

// Sleep for up to 1 second 

ThreadUtils.pause(Math.random()); 

} 

} 

This example is just for testing, so the output will go in the DDMS window. The next tutorial section will talk about what to do if 

the results of the background threads directly affect the user interface.

Helper Class 

public class ThreadUtils { 

public static void pause(double seconds) { 

try { 

Thread.sleep(Math.round(1000.0 * seconds)); 

} catch (InterruptedException ie) {} 

} 

} 

692 


// Uninstantiable class: static methods only 

private ThreadUtils() {}

Thread Mechanism One: Results 

pool-2-thread-1: 0 















693 

jeudi 26 janvier 12

Pros and Cons of Approach 


– Loose coupling 

• Can change pieces independently 

• Can reuse Runnable class in more than one application 

– Passing arguments 

• If you want different threads to do different things, you pass args to 

constructor, which stores them in instance variables that run method uses 

– Little danger of race conditions 

• You usually use this approach when there is no data shared among 

threads, so no need to synchronize. 

• Disadvantages 

– Hard to access main Activity 

• If you want to call methods in main app, you must 

694 


– Pass reference to main app to the Runnable’s constructor, which stores it 

– Make methods in main app be public

695 


Approach Two: Main 

App Implements 

Runnable 





Review of Interfaces: Syntax 

• Shape interface 

public interface Shape { 

} 

public double getArea(); // No body, just specification 

• Circle class 

public class Circle implements Shape { 

} 

• Note 

696 


public double getArea() { some real code } 

–You can implement many interfaces 

• public class MyClass implements Foo, Bar, Baz { … }

Review of Interfaces: Benefits 

• Class can be treated as interface type 

697 


–public interface Shape { 

public double getArea(); 

} 

–public class Circle implements Shape { … } 

–public class Rectangle implements Shape { … } 

Shape[] shapes = 

{ new Circle(…), new Rectangle(…) … }; 

double sum = 0; 

for(Shape s: shapes) { 

sum = sum + s.getArea(); // All Shapes have getArea 

}

Thread Mechanism Two: 

Main App Implements Runnable 

• Have main class implement Runnable 

– Put actions in run method of existing class 

• public class MyClass extends Activity implements Runnable { 

… 


} 

• Pass the instance of main class to execute 

– taskList.execute(this); 

• Main differences from previous approach 

– Good 

• run can easily call methods in main class, since it is in that class 

– Bad 

• If run accesses any shared data (instance variables), you have to 

worry about conflicts (race conditions) 

• Very hard to pass arguments, so each task starts off the same 

698 

jeudi 26 janvier 12

Main App Implements Runnable: 

Template Code 

699 

public class ThreadedActivity extends Activity 

implements Runnable { 


// Code to run in background. Don’t update UI. 

} 

} 






for(int i=0; i

Thread Mechanism Two: Example 

public class ThreadingBasicsActivity extends Activity 


private final static int LOOP_LIMIT = 5; 

700 


public void implementsInterface(View clickedButton) { 



taskList.execute(this); 


} 


This method is associated with 

a Button via the 


layout file. 



for (int i = 0; i < LOOP_LIMIT; i++) { 

String threadName = Thread.currentThread().getName(); 



} 

}

Thread Mechanism Two: Results 
















701 

jeudi 26 janvier 12



–Easy to access main app. 

• The run method is already inside main app. Can access any 

public or private methods or instance variables. 


702 


–Tight coupling 

• run method tied closely to this application 

–Cannot pass arguments to run 

• So, you either start a single thread only (quite common), or all 

the threads do very similar tasks 

–Danger of race conditions 

• You usually use this approach specifically because you want to 

access data in main application. So, if run modifies some shared 

data, you must synchronize.

703 



Approach Three: Inner 

Class that Implements 

Runnable 




Review of Inner Classes 

• Class can be defined inside another class 

– Methods in the inner class can access all methods and instance 

variables of surrounding class 

• Even private methods and variables 

• Example 

public class OuterClass { 

private int count = …; 

704 


} 

public void foo(…) { 

InnerClass inner = new InnerClass(); 

inner.bar(); 

} 

private class InnerClass { 

public void bar() { 

doSomethingWith(count); 

} 

}

Thread Mechanism Three: 

Runnable Inner Class 

• Have inner class implement Runnable 

–Put actions in run method of inner class 

• public class MyClass extends Activity { 

… 

private class SomeInnerClass implements Runnable { 


} 

} 

• Pass instances of inner class to execute 

705 


–taskList.execute(new SomeInnerClass(…));

Inner Class Implements 

Runnable: Template Code 

706 


public class MainClass extends Activity { 





for(int i=0; i


Example 

public class ThreadingBasicsActivity extends Activity { 




setContentView(R.layout.threading_basics); 

} 

707 


public void innerClass(View clickedButton) { 



taskList.execute(new InnerCounter(6)); 



} 

This method is associated with a Button via the 

android:onClick attribute in the layout file. Note 

also that the class is not yet finished – inner class 

on next page is still inside this class.

} 


Example (Continued) 

708 


private class InnerCounter implements Runnable { 

private final int mLoopLimit; 

} 

public InnerCounter(int loopLimit) { 

this.mLoopLimit = loopLimit; 

} 


for (int i = 0; i < mLoopLimit; i++) { 

String threadName = 

Thread.currentThread().getName(); 



} 

} 

You can also use anonymous inner classes. This is not different enough to warrant a separate 

example here, especially since we showed examples in the section on Widget event handling.


Results 
















709 

jeudi 26 janvier 12



–Easy to access main app. 

• Methods in inner classes can access any public or private 

methods or instance variables of outer class. 

–Can pass arguments to run 

• As with separate classes, you pass args to constructor, which 

stores them in instance variables that run uses 


710 


–Tight coupling 

• run method tied closely to this application 

–Danger of race conditions 

• You usually use this approach specifically because you want to 

access data from main application. So, if run modifies some 

shared data, you must synchronize.

711 



Summary of Approaches 




Pros and Cons 

• Separate class that implements Runnable 

–Can pass args to run 

–Cannot easily access data in main class 

–Usually no worry about race conditions 

• Main class implements Runnable 

–Can easily access data in main class 

–Cannot pass args to run 

–Must worry about race conditions 

• Inner class implements Runnable 

712 


–Can easily access data in main class 

–Can pass args to run 

–Must worry about race conditions

713 


Race Conditions and 

Synchronization 





Race Conditions 


– You write code that assumes no other threads run between certain 

steps. But, if your thread is interrupted in the wrong place and 

another thread changes some data, you get the wrong answer. 

• Typical scenarios 

– You modify shared data & assume next thread sees new result. 

• You read a value and then increment it. You assume no thread runs 

between when you read it and when you increment it. 

– You read shared data and then use it, forgetting that it could 

change between when you read it and when you use it 

• You look up size of a List, then loop from 0 to size-1. But, another 

thread could remove elements in between. 

714 

jeudi 26 janvier 12

Race Conditions: Example 

public class RaceConditionsActivity extends Activity 


private final static int LOOP_LIMIT = 3; 

private final static int POOL_SIZE = 4; 

private int mLatestThreadNum = 0; 

715 





setContentView(R.layout.race_conditions); 

} 

public void tryRace(View clickedButton) { 


Executors.newFixedThreadPool(POOL_SIZE); 

for(int i=0; i

} 

Race Conditions: Example 

(Continued) 


int currentThreadNum = mLatestThreadNum; 

System.out.printf("Setting currentNum to %s%n", 

currentThreadNum); 

mLatestThreadNum = mLatestThreadNum + 1; 


System.out.printf("I am Counter %s; i is %s%n", 

currentThreadNum, i); 

ThreadUtils.pause(0.5 * Math.random()); 

} 

} 

• What’s wrong with this code? 

716 

jeudi 26 janvier 12

Race Conditions: Result 

• Usual Output 

Setting currentNum to 0 

I am Counter 0; i is 0 















717 


• Occasional Output 
















I am Counter 38; i is 2

Race Conditions: Solution? 

• Do things in a single step 

718 



int currentThreadNum = mLatestThreadNum++; 




System.out.printf("I am Counter %s; i is %s%n", 

currentThreadNum, i); 

ThreadUtils.pause(0.5 * Math.random()); 

} 

} 

This “solution” does not fix the problem. In some ways, it makes it worse!

Arbitrating Contention for Shared 

Resources 

• Synchronizing a section of code 

synchronized(someObject) { 

code 

} 

• Fixing the previous race condition 


int currentThreadNum; 

synchronized(this) { 

currentThreadNum = mLatestThreadNum; 



mLatestThreadNum = mLatestThreadNum + 1; 

} 


... 

} 

} 

719 

jeudi 26 janvier 12


Resources 

• Synchronizing a section of code 

synchronized(someObject) { 

code 

} 

• Simplistic interpretation 

–Once a thread enters the code, no other thread can enter until 

the first thread exits. 

• Stronger interpretation 

720 


–Once a thread enters the code, no other thread can enter any 

section of code that is synchronized using the same “lock” 

object 

• If two pieces of code say “synchronized(blah)”, the question is if 

the blah’s are the same object instance.


Resources 

• Synchronizing an entire method 

public synchronized void someMethod() { 

body 

} 

• Note that this is equivalent to 

721 


public void someMethod() { 

synchronized(this) { 

body 

} 

}

722 



Helpful Thread-Related 

Methods 




Methods in Thread Class 

• Thread.currentThread() 

–Gives instance of Thread that is running current code 

• Thread.sleep(milliseconds) 

–Puts calling code to sleep. Useful for non-busy waiting in all 

kinds of code, not just multithreaded code. You must catch 

InterruptedException, but you can ignore it: 

• try { Thread.sleep(someMilliseconds); } 

catch (InterruptedException ie) { } 

–See also TimeUnit.SECONDS.sleep, 

TimeUnit.MINUTES.sleep, etc. 

• Same idea except takes sleep time in different units. 

• someThread.getName(), someThread.getId() 

723 


–Useful for printing/debugging, to tell threads apart

Methods in ExecutorService 

Class 

• execute(Runnable) 

– Adds Runnable to the queue of tasks 

• shutdown 

– Prevents any more tasks from being added with execute (or 

submit), but lets current tasks finish. 

• shutdownNow 

– Attempts to halt current tasks. But author of tasks must have them 

respond to interrupts (ie, catch InterruptedException), or this is 

no different from shutdown. 

• awaitTermination 

– Blocks until all tasks are complete. Must shutdown() first. 

• submit, invokeAny, invokeAll 

– Variations that use Callable instead of Runnable. See next slide 

on Callable. 

724 

jeudi 26 janvier 12

Callable 

• Runnable 

–“run” method runs in background. No return values, but run 

can do side effects. 

–Use “execute” to put in task queue 

• Callable 

725 


–“call” method runs in background. It returns a value that can 

be retrieved after termination with “get”. 

–Use “submit” to put in task queue. 

–Use invokeAny and invokeAll to block until value or values 

are available 

• Example: you have a list of links from a Web page and want to 

check status (404 vs. good). Submit them to a task queue to run 

concurrently, then invokeAll will let you see return values when 

all links are done being checked.

Lower-Level Threading 

• Use Thread.start(someRunnable) 

– Implement Runnable, pass to Thread constructor, call start 

• Thread t = new Thread(someRunnable); 

• t.start(); 

– About same effect as taskList.execute(someRunnable), except 

that you cannot put bound on number of simultaneous threads. 

– Mostly a carryover from pre-Java-5 days; still widely used. 

• Extend Thread 

– Put run method in Thread subclass, instantiate, call start 

• SomeThreadSubclass t = new SomeThreadSubclass(…); 

• t.start(); 

– A holdover from pre-Java-5; has little use in modern Java 

applications (Android or otherwise) 

726 

jeudi 26 janvier 12

727 


Advanced Topics 





Types of Task Queues 

• Executors.newFixedThreadPool(nThreads) 

– Simplest and most widely used type. Makes a list of tasks to be run in the 

background, but with caveat that there are never more than nThreads 

simultaneous threads running. 

• Executors.newScheduledThreadPool 

– Lets you define tasks that run after a delay, or that run periodically. 

Replacement for pre-Java-5 “Timer” class. 

• Executors.newCachedThreadPool 

– Optimized version for apps that start many short-running threads. Reuses 

thread instances. 

• Executors.newSingleThreadExecutor 

– Makes queue of tasks and executes one at a time 

• ExecutorService (subclass) constructors 

– Lets you build FIFO, LIFO, and priority queues 

728 

jeudi 26 janvier 12

Stopping a Thread 

public class SomeTask implements Runnable { 

private volatile boolean running; 

} 

729 


public void run(){ 

running = true; 

while (running) { 

... 

} 

doCleanup(); 

} 

public void setRunning(boolean running) { 

this.running = running; 

} 

Compilers on multicore systems often do optimizations that prevent changes to 

variables from one thread from being seen by another thread. To guarantee that 

other threads see your changes, either use synchronized methods, declare the 

variable “volatile”, or use AtomicBoolean.

Nasty Synchronization Bug 

public class Driver { 

public void startThreads() { 

… 

for(…) { 

taskList.execute(new SomeThreadedClass()); 

}}} 

public class SomeThreadedClass implements Runnable { 

public synchronized void doSomeOperation() { 

accessSomeSharedObject(); 

} 

... 


while(someCondition) { 

doSomeOperation(); // Accesses shared data 

doSomeOtherOperation();// No shared data 

} 

} 

} 

730 

jeudi 26 janvier 12

Synchronization Solution 

• Solution 1: synchronize on the shared data 

public void doSomeOperation() { 

synchronized(someSharedObject) { 


} 

} 

• Solution 2: synchronize on the class object 


synchronized(SomeThreadedClass.class) { 


} 

} 

731 


– Note that if you synchronize a static method, the lock is the 

corresponding Class object, not this

Synchronization Solution 

(Continued) 

• Solution 3: synchronize on arbitrary object 

732 


public class SomeThreadedClass 

implements Runnable{ 

private static Object lockObject 

= new Object(); 

... 


synchronized(lockObject) { 


} 

} 

... 

} 

– Why doesn’t this problem usually occur with thread mechanism 

two (with run method in main class)?

Determining Maximum Thread 

Pool Size 

• In most apps, a reasonable guess is fine 

int maxThreads = 50; 

ExecutorService tasks = 

Executors.newFixedThreadPool(maxThreads); 

• For more precision, you can use equation 

733 


maxThreads = numCpus * targetUtilization * 

(1 + avgWaitTime/avgComputeTime) 

• Compute numCpus with 

Runtime.getRuntime().availableProcessors() 

• targetUtilization is from 0.0 to 1.0 

• Find ratio of wait to compute time with profiling 

• Equation taken from Java Concurrency in Practice

Other Advanced Topics 

• wait/waitForAll 

– Releases the lock for other threads and suspends itself (placed in a wait 

queue associated with the lock) 

– Very important in some applications, but very, very hard to get right. Try 

to use the newer Executor services if possible. 

• notify/notifyAll 

– Wakes up all threads waiting for the lock 

– A notified thread doesn’t begin immediate execution, but is placed in the 

runnable thread queue 

• Concurrency utilities in java.util.concurrency 

– Advanced threading utilities including semaphores, collections designed 

for multithreaded applications, atomic operations, etc. 

• Debugging thread problems 

– Use JConsole (bundled with Java 5; officially part of Java 6) 

• http://java.sun.com/developer/technicalArticles/J2SE/jconsole.html 

734 

jeudi 26 janvier 12


Wrap-Up 





More Reading 

• Books 

–Java Concurrency in Practice (Goetz, et al) 

–Chapter 10 (“Concurrency”) of Effective Java, 2 nd Ed (Josh 

Bloch) 

• Effective Java is the alltime best Java practices book 

–Java Threads (Oak and Wong) 

• Online references 

736 


–Lesson: Concurrency (Oracle Java Tutorial) 

• http://download.oracle.com/javase/tutorial/essential/concurrency/ 

–Jacob Jenkov’s Concurrency Tutorial 

• http://tutorials.jenkov.com/java-concurrency/index.html 

–Lars Vogel’s Concurrency Tutorial 

• http://www.vogella.de/articles/JavaConcurrency/article.html

Summary 

• Basic approach 



• Three variations 

–taskList.execute(new SeparateClass(…)); 

–taskList.execute(this); 

–taskList.execute(new InnerClass(…)); 

• Handling shared data 

737 


synchronized(referenceSharedByThreads) { 

} 

getSharedData(); 

modifySharedData(); 

doOtherStuff();



Multithreaded Programming Part II: 

Android-Specific Techniques 







• GUI update guidelines 

• Updating UI after threads complete 

• Downloading images from Internet 

• Updating UI with View.post 

• Updating UI with AsyncTask 

739 

jeudi 26 janvier 12

740 


Overview 





Issues 

• Nonresponsive GUI controls 

–Long-running code in main thread will make GUI controls 

nonresponsive. 

• Threads cannot update user interface 

741 


–Background threads are prohibited from updating UI.

Nonresponsive GUI Controls 

• Problem 

–Long-running code in main thread will make GUI controls 

nonresponsive. 

• For example, if a Button’s onClick handler takes 5 seconds, then 

none of the other controls will respond for 5 seconds. 

• Solution 

742 


–Move time-consuming operations to background threads 

• This was the entire point of the previous lecture on the basics of 

multithreaded programming

Threads Cannot Update UI 

• Problem 

– Background threads are prohibited from updating UI. 

• E.g., background threads cannot add a new View to the display, nor can 

they call setText on a visible View. 

• Solutions (alternatives) 

– Wait until all threads are done, then update UI 

743 


• When multithreading improves performance, but total wait time is small 

– Have background threads use View.post to send UI-updating operations 

back to UI thread 

• Especially when transitioning standard threading code to Android 

– Use AsyncTask to divide tasks between background and UI threads 

• Especially when developing for Android from beginning and you have a lot 

of incremental GUI updates.


Updating UI After 

Threads Complete 





Updating UI All at Once 

• Scenario 

–Using threads improves performance. 

–Total wait time is small, so no need to display intermediate 

results. 

• Approach 

745 


–Add threads to ExecutorService task list. 

–Use awaitTermination to wait until all tasks are finished (or a 

timeout is exceeded) 

–Update UI. You are in UI thread, so this is safe/legal.

Example: Multi-URL Validator 


–Let user enter any number of URLs 

–Check if they are legal by making HTTP HEAD requests and 

checking the server status line 

• Approach 

746 


–Make a List of URL result holders 

–For each URL, pass result holder to background thread. 

Background thread stores result in holder. Use inner class for 

background thread implementation. 

–After all tasks are complete or 10 seconds have elapsed 

(whichever is sooner), show results in ScrollView

Main Activity: Setup Code 

public class UrlCheckerActivity extends Activity { 

private LinearLayout mResultsRegion; 

private EditText mUrlsToTest; 

private int mGoodUrlColor, mForwardedUrlColor, 

mBadUrlColor; 

private Drawable mGoodUrlIcon, mForwardedUrlIcon, 

mBadUrlIcon; 

List mResultsHolder = 

new ArrayList(); 

private final static int HEAD_TIMEOUT = 10; 

private float mResultTextSize; 

private int mResultPaddingSize; 

747 

jeudi 26 janvier 12


(Continued) 

748 





setContentView(R.layout.url_checker); 

mUrlsToTest = (EditText)findViewById(R.id.urls_to_test); 

mResultsRegion = (LinearLayout)findViewById(R.id.results_region); 


mGoodUrlColor = resources.getColor(R.color.url_good); 

mForwardedUrlColor = resources.getColor(R.color.url_forwarded); 

mBadUrlColor = resources.getColor(R.color.url_bad); 

mGoodUrlIcon = resources.getDrawable(R.drawable.emo_im_happy); 

mForwardedUrlIcon = resources.getDrawable(R.drawable.emo_im_wtf); 

mBadUrlIcon = resources.getDrawable(R.drawable.emo_im_sad); 

mResultTextSize = 

resources.getDimension(R.dimen.url_checker_result_size); 

mResultPaddingSize = 

(int)resources.getDimension(R.dimen.url_checker_padding_size);

Main Activity: Button Handler 

(Starts Threads) 

749 


public void checkUrls(View clickedButton) { 

mResultsRegion.removeAllViews(); 

mResultsRegion.requestLayout(); 

String[] urls = 

mUrlsToTest.getText().toString().split("\\s+"); 



for (String url: urls) { 

UrlCheckerResult resultHolder = 

new UrlCheckerResult(url); 

mResultsHolder.add(resultHolder); 

taskList.execute(new UrlTester(resultHolder)); 

} 

try { 

taskList.shutdown(); 

taskList.awaitTermination(HEAD_TIMEOUT, 

TimeUnit.SECONDS); 

} catch (InterruptedException e) {}


(After Threads Complete) 

750 


for(UrlCheckerResult resultHolder: mResultsHolder) { 

UrlChecker result = resultHolder.getUrlResult(); 

if (result == null) { 

result = 

new UrlChecker(resultHolder.getUrlString(), 

HEAD_TIMEOUT); 

} 

TextView displayedResult = new TextView(this); 

displayedResult.setTextColor(chooseColor(result)); 

displayedResult.setTextSize(mResultTextSize); 

displayedResult.setText(result.toString()); 

displayedResult.setCompoundDrawablesWithIntrinsicBounds 

(chooseIcon(result), null, null, null); 

displayedResult.setCompoundDrawablePadding 

(mResultPaddingSize); 

mResultsRegion.addView(displayedResult); 

} 

} 

It would have been be illegal to do this in the background 

thread, because it changes the visible UI. Creating the 

TextView would have been legal, but adding it to the 

vertical LinearLayout inside the ScrollView (as done here) 

would have been illegal.

Main Activity: 

Runnable Inner Class 

751 


private class UrlTester implements Runnable { 

private UrlCheckerResult mResultHolder; 

} 

public UrlTester(UrlCheckerResult resultHolder) { 

mResultHolder = resultHolder; 

} 


UrlChecker result = 

new UrlChecker(mResultHolder.getUrlString()); 

mResultHolder.setUrlResult(result); 

} 

The run method does not update the UI directly. Instead, it updates a data 

structure that will later be read and then used to update the UI (code that 

does this was shown on previous slide). 

The UrlChecker class does the actual network calls. Since different servers can respond 

at different speeds, calling UrlChecker in a background thread can substantially improve 

performance.

Main Activity: 

Helper Methods 

752 


private int chooseColor(UrlChecker urlResult) { 

if (urlResult.isGood()) { 

return(mGoodUrlColor); 

} else if (urlResult.isForwarded()) { 

return(mForwardedUrlColor); 

} else { 

return(mBadUrlColor); 

} 

} 

private Drawable chooseIcon(UrlChecker urlResult) { 

if (urlResult.isGood()) { 

return(mGoodUrlIcon); 

} else if (urlResult.isForwarded()) { 

return(mForwardedUrlIcon); 

} else { 

return(mBadUrlIcon); 

} 

} 

I use different text colors and different icons depending on 

whether the URL is good, forwarded, or bad.

Main Helper Classes 

• UrlChecker 

–Makes a HEAD request and parses status line. If status code 

is 301 or 302, looks up Location header. 

• Most of the code shown in earlier lecture on Networking 

• UrlCheckerResult 

753 


–Stores a URL and the associated UrlChecker result. 

• The timeout could be exceeded before the results are found, in 

which case the UrlChecker is null. In that scenario, we display a 

message that shows the URL and says that no result was found 

within the allotted time.

Results 

754 

jeudi 26 janvier 12


Downloading 

Web Images 





Displaying a Network Image 


–The decodeStream method of BitmapFactory can take an 

InputStream and produce a Bitmap. You can put a Bitmap into 

an ImageView 

• Approach 

756 


–Get an HttpURLConnection (as explained in second 

networking lecture) 

–Get the input stream with connection.getInputStream() 

–Pass the stream to BitmapFactory.decodeStream and store 

result in Bitmap 

–Get a reference to an ImageView and pass new Bitmap to 

setImageBitmap

BitmapUtils: Getting a Bitmap 

public class BitmapUtils { 

public static Bitmap bitmapFromUrl(String urlString) 

throws MalformedURLException, IOException { 

URL url = new URL(urlString); 

HttpURLConnection urlConnection = 

(HttpURLConnection)url.openConnection(); 

InputStream in = urlConnection.getInputStream(); 

Bitmap bitmapImage = BitmapFactory.decodeStream(in); 

urlConnection.disconnect(); 

return(bitmapImage); 

} 

757 

jeudi 26 janvier 12

Making a View for an Image 


–Given an address, try to load a Bitmap from it. If successful, 

make an ImageView showing the Bitmap. If unsuccessful, 

make a TextView showing information on the error. 

• Approach 

758 


–Call BitmapUtils.bitmapFromUrl. 

• If no Exception, instantiate ImageView and pass Bitmap to 

setImageBitmap. 

• If Exception, instantiate TextView and store an error message in 

it.

BitmapUtils: 

Getting a View for an Image 

public static View viewForImage(String urlString, Context context) { 

Bitmap bitmapImage = null; 

String errorMessage = ""; 

try { 

bitmapImage = BitmapUtils.bitmapFromUrl(urlString); 

} catch (MalformedURLException mue) { 

errorMessage = String.format("Malformed URL %s", urlString); 


errorMessage = String.format("Error downloading image: %s", 

ioe.getMessage()); 

} 

if (bitmapImage != null) { 

ImageView displayedImage = new ImageView(context); 

displayedImage.setImageBitmap(bitmapImage); 

displayedImage.setPadding(5, 5, 5, 5); 

return(displayedImage); 

} else { 

TextView displayedMessage = new TextView(context); 

displayedMessage.setText(errorMessage); 

return(displayedMessage); 

} 

} 

759 

jeudi 26 janvier 12

Example: 

Unthreaded Image Viewer 


–Let user enter URL of an image to be displayed 

–Either show that image, or show error message 

• Approach 

760 


–Read the address from EditText, pass to 

BitmapUtils.viewForImage 

–Add resultant View to the layout

Activity 

public class SimpleImageDownloaderActivity extends Activity { 

private LinearLayout mMainWindow; 

private EditText mImageToDownload; 

private View mViewForImage; 

} 

761 





setContentView(R.layout.simple_image_downloader); 

mMainWindow = (LinearLayout)findViewById(R.id.main_window); 

mImageToDownload = 

(EditText)findViewById(R.id.image_to_download); 

} 

public void downloadImage(View clickedButton) { 

if (mViewForImage != null) { 

mMainWindow.removeView(mViewForImage); 

} 

String imageUrl = mImageToDownload.getText().toString(); 

mViewForImage = BitmapUtils.viewForImage(imageUrl, this); 

mMainWindow.addView(mViewForImage); 

}

Results 

762 

jeudi 26 janvier 12


Updating UI with 

View.post 





View.post 

• Scenario 

–Total wait time might be large, so you want to show 

intermediate results 

–You have a lot of normal threading code but you occasionally 

need to update UI. 

• Approach 

764 


–When background thread has result that should affect UI, 

create a Runnable and pass to post 

public void run() { // Background thread 

doStuffButDontUpdateUI(); 

someView.post(new Runnable() { 

public void run() { updateUI(); }}); 

}

Example: Multithreaded Image 

Viewer (Version 1) 


–Let user enter URLs of images to be displayed 

–Download and display them inside a scrolling horizontal 

LinearLayout 

• Approach 

765 


–Download images and associate them with ImageView, as 

shown in the previous subsection. If there was an error, create 

a TextView saying so. 

–Create a Runnable that will add the resultant View to the 

LinearLayout 

–Pass that Runnable to the post method of the LinearLayout


public class ImageDownloader1Activity extends Activity { 

protected LinearLayout mResultsRegion; 

protected EditText mImagesToDownload; 

766 





setContentView(R.layout.image_downloader); 

mImagesToDownload = 

(EditText)findViewById(R.id.images_to_download); 

mResultsRegion = 

(LinearLayout)findViewById(R.id.results_region); 

}


767 


public void downloadImages(View clickedButton) { 

mResultsRegion.removeAllViews(); 

mResultsRegion.requestLayout(); 

String[] images = 

mImagesToDownload.getText().toString().split("\\s+"); 

addImages(images); 

} 

protected void addImages(String[] images) { 



for (String image: images) { 

taskList.execute(new ImageDownloader(image)); 

} 

} 

The event handler is split into two methods because the next 

example will extend this class and override addImages, but 

will keep the inherited version of downloadImages 

unchanged.

Main Activity: Runnable Inner 

Class (For Background) 

768 

private class ImageDownloader implements Runnable { 

private String mImageUrl; 

} 


public ImageDownloader(String imageUrl) { 

mImageUrl = imageUrl; 

} 


View viewToAdd = 

BitmapUtils.viewForImage(mImageUrl, 

ImageDownloader1Activity.this); 

mResultsRegion.post(new ViewAdder(viewToAdd)); 

} 

This is the task that the ExecutorService executes. It calls viewForImage, a time-consuming 

task that loads an image from the network and associates it with an ImageView (or a 

TextView if there was an error). The View is then sent to the main UI thread by putting it in a 

Runnable and passing the Runnable to the post method of a View that is in the main Activity.

Main Activity: Runnable Inner 

Class (For UI Thread) 

769 


private class ViewAdder implements Runnable { 

private View mViewToAdd; 

} 

public ViewAdder(View viewToAdd) { 

mViewToAdd = viewToAdd; 

} 


mResultsRegion.addView(mViewToAdd); 

} 

This changes the UI, so could not have been 

done in the background.

Results 

770 

jeudi 26 janvier 12


Updating UI with 

AsyncTask 





AsyncTask 

• Scenario 

– Total wait time might be large, so you want to show intermediate 

results 

– You are designing code from the beginning to divide the work 

between GUI and non-GUI code 

• Approach 

– Use AsyncTask with doInBackground & onPostExecute 

772 


private class MixedTask extends AsyncTask { 

public SomeType doInBackground(…) { 

doNonGuiStuff(); 

return(valueForUiThread); 

} 

public void onPostExecute(SomeType valueForUiThread) { 

doGuiStuffWith(valueForUiThread); 

} 

}

AsyncTask: Quick Example 

• Task itself 

private class ImageDownloadTask extends AsyncTask { 

public View doInBackground(String... urls) { 

return(BitmapUtils.viewForImage(urls[0], MainActivity.this)); 

} 

} 

public void onPostExecute(View viewToAdd) { 

mResultsRegion.addView(viewToAdd); 

} 

• Invoking task 

String imageAddress = "http://…"; 

ImageDownloadTask task = new ImageDownloadTask(); 

task.execute(imageAddress); 

773 

jeudi 26 janvier 12

AsyncTask Details: Constructor 

• Class is genericized with three arguments 

– AsyncTask 

• Interpretation 

– ParamType 

• This is the type you pass to execute, which in turn is the type that is 

send to doInBackground. Both methods use varargs, so you can send 

any number of params. 

– ProgressType 

• This is the type that you pass to publishProgress, which in turn is 

passed to onProgressUpdate (which is called in UI thread). Use Void 

if you do not need to display intermediate progress. 

– ResultType 

• This is the type that you should return from doInBackground, which in 

turn is passed to onPostExecute (which is called in UI thread). 

774 

jeudi 26 janvier 12

AsyncTask Details: 

doInBackground 


–This is the code that gets executed in the background. It 

cannot update the UI. 

–It takes as arguments whatever was passed to execute 

–It returns a result that will be later passed to onPostExecute in 

the UI thread. 


private class SomeTask extends AsyncTask { 

public Type2 doInBackground(Type1... params) { 

return(doNonUiStuffWith(params)); 

} ... 

} 

… 

775 


new SomeTask().execute(type1VarA, type1VarB); 

The … in the doInBackground declaration is actually part 

of the Java syntax, indicating varargs.


doPostExecute 


–This is the code that gets executed by the UI thread. It can 

update the UI. 

–It takes as an argument whatever was returned by 

doInBackground 


private class SomeTask extends AsyncTask { 

public Type2 doInBackground(Type1... params) { 

return(doNonUiStuffWith(params)); 

} 

public void doPostExecute(Type2 result) { doUiStuff(result); } 

} 

… 

new SomeTask().execute(type1VarA, type1VarB); 

776 

jeudi 26 janvier 12


Other Methods 

• onPreExecute 

–Invoked by the UI thread before doInBackground starts 

• publishProgress 

–Sends an intermediate update value to onProgressUpdate. You 

call this from code that is in doInBackground. The type is the 

middle value of the class declaration. 

• onProgressUpdate 

–Invoked by the UI thread. Takes as input whatever was passed 

to publishProgress. 

• Note 

777 


–All of these methods can be omitted.

Example: Multithreaded Image 

Viewer (Version 2) 


–Let user enter URLs of images to be displayed 

–Download and display them inside a scrolling horizontal 

LinearLayout 

• Approach 

778 


–Extend previous example. Make an AsyncTask 

–doInBackground 

• Download images and associate them with ImageView, as shown 

in the previous subsection. If there was an error, create a 

TextView saying so. Return that View. 

–doPostExecute 

• Add the View to the LinearLayout

Activity 

public class ImageDownloader2Activity extends ImageDownloader1Activity { 


protected void addImages(String[] images) { 

for (String image: images) { 

ImageDownloadTask task = new ImageDownloadTask(); 

task.execute(image); 

} 

} 

} 

779 

private class ImageDownloadTask extends AsyncTask { 


public View doInBackground(String... urls) { 

return(BitmapUtils.viewForImage(urls[0], 

ImageDownloader2Activity.this)); 

} 

} 



public void onPostExecute(View viewToAdd) { 

mResultsRegion.addView(viewToAdd); 

}

Results 

780 

jeudi 26 janvier 12


Wrap-Up 





More Reading 

• JavaDoc 

–AsyncTask 

• http://developer.android.com/reference/android/os/AsyncTask.html 

• Tutorial: Processes and Threads 

–http://developer.android.com/guide/topics/fundamentals/ 

processes-and-threads.html 

• Chapters 

782 


–Threads, Services, Receivers, and Alerts 

• From The Android Developer’s Cookbook by Steele & To 

–Dealing with Threads 


by Mark Murphy (http://commonsware.com/Android/)

Summary 

• Update UI after all threads done 

–Use taskList.awaitTermination 

• Update UI incrementally with post 

–Main thread does non-GUI stuff. Sends values for UI thread 

via someView.post(someRunnable) 

• Update UI incrementally with AsyncTask 

–doInBackground 

• Does non-GUI stuff. Returns value for UI thread. 

–doPostExecute 

• Does GUI stuff. Uses value from doInBackground 

• Loading images from network 

783 


–Use HttpURLConnection & BitmapFactory.decodeStream

David Defour - Université de Perpignan

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