Android™ Application Development - Bahar Ali Khan

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Chapter 3: Creating Applications and Activities What Makes an Android Application? 46 Android applications consist of loosely coupled components, bound using a project manifest that describes each component and how they interact. There are six components that provide the building blocks for your applications: ❑ Activities Your application’s presentation layer. Every screen in your application will be an extension of the Activity class. Activities use Views to form graphical user interfaces that display information and respond to user actions. In terms of desktop development, an Activity is equivalent to a Form. You’ll learn more about Activities later in this chapter. ❑ Services The invisible workers of your application. Service components run invisibly, updating your data sources and visible Activities and triggering Notifi cations. They’re used to perform regular processing that needs to continue even when your application’s Activities aren’t active or visible. You’ll learn how to create Services in Chapter 8. ❑ Content Providers A shareable data store. Content Providers are used to manage and share application databases. Content Providers are the preferred way of sharing data across application boundaries. This means that you can confi gure your own Content Providers to permit access from other applications and use Content Providers exposed by others to access their stored data. Android devices include several native Content Providers that expose useful databases like contact information. You’ll learn how to create and use Content Providers in Chapter 6. ❑ Intents A simple message-passing framework. Using Intents, you can broadcast messages system-wide or to a target Activity or Service, stating your intention to have an action performed. The system will then determine the target(s) that will perform any actions as appropriate. ❑ Broadcast Receivers Intent broadcast consumers. By creating and registering a Broadcast Receiver, your application can listen for broadcast Intents that match specifi c fi lter criteria. Broadcast Receivers will automatically start your application to respond to an incoming Intent, making them ideal for event-driven applications. ❑ Notifi cations A user notifi cation framework. Notifi cations let you signal users without stealing focus or interrupting their current Activities. They’re the preferred technique for getting a user’s attention from within a Service or Broadcast Receiver. For example, when a device receives a text message or an incoming call, it alerts you by fl ashing lights, making sounds, displaying icons, or showing dialog messages. You can trigger these same events from your own applications using Notifi cations, as shown in Chapter 8. By decoupling the dependencies between application components, you can share and interchange individual pieces, such as Content Providers or Services, with other applications — both your own and those of third parties. Introducing the Application Manifest Each Android project includes a manifest fi le, AndroidManifest.xml, stored in the root of the project hierarchy. The manifest lets you defi ne the structure and metadata of your application and its components.
Chapter 3: Creating Applications and Activities It includes nodes for each of the components (Activities, Services, Content Providers, and Broadcast Receivers) that make up your application and, using Intent Filters and Permissions, determines how they interact with each other and other applications. It also offers attributes to specify application metadata (like its icon or theme), and additional top-level nodes can be used for security settings and unit tests as described below. The manifest is made up of a root manifest tag with a package attribute set to the project’s package. It usually includes an xmlns:android attribute that supplies several system attributes used within the fi le. A typical manifest node is shown in the XML snippet below: [ ... manifest nodes ... ] The manifest tag includes nodes that defi ne the application components, security settings, and test classes that make up your application. The following list gives a summary of the available manifest node tags, and an XML snippet demonstrating how each one is used: ❑ application A manifest can contain only one application node. It uses attributes to specify the metadata for your application (including its title, icon, and theme). It also acts as a container that includes the Activity, Service, Content Provider, and Broadcast Receiver tags used to specify the application components. [ ... application nodes ... ] ❑ activity An activity tag is required for every Activity displayed by your application, using the android:name attribute to specify the class name. This must include the main launch Activity and any other screen or dialogs that can be displayed. Trying to start an Activity that’s not defi ned in the manifest will throw a runtime exception. Each Activity node supports intent-filter child tags that specify which Intents launch the Activity. ❑ service As with the activity tag, create a new service tag for each Service class used in your application. (Services are covered in detail in Chapter 8.) Service tags also support intent-filter child tags to allow late runtime binding. 47
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Professional Android Application su
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Professional Android Application D
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Professional Android Application D
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About the Author Originally from Pe
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Acknowledgments A big thank you goe
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Contents Chapter 2: Getting Started
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Contents xii Saving and Loading Fil
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Contents Chapter 10: Accessing Andr
Page 19 and 20: Introduction Now is an exciting tim
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Data Storage, Retrieval, and Sharin
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Chapter 6: Data Storage, Retrieval,
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Querying Your Database Chapter 6: D
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Adding, Updating, and Deleting Cont
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Maps, Geocoding, and Location-Based
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Chapter 7: Maps, Geocoding, and Loc
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Summary Chapter 7: Maps, Geocoding,
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Chapter 8: Working in the Backgroun
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Accessing Android Hardware Android
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Chapter 11: Advanced Android Develo
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400 Android, getting started Androi
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402 databases databases creating ea
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Programmer to Programmer Get more
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Android™ Application Development - Bahar Ali Khan

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