Android™ Application Development - Bahar Ali Khan

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Chapter 4: Creating User Interfaces 80 The following XML snippet shows a simple layout that places a TextView above an EditText control using a LinearLayout confi gured to lay out vertically: Implementing layouts in XML decouples the presentation layer from View and Activity code. It also lets you create hardware-specifi c variations that are dynamically loaded without requiring code changes. When it’s preferred, or required, you can implement layouts in code. When assigning Views to layouts, it’s important to apply LayoutParameters using the setLayoutParams method, or passing them in to the addView call as shown below: LinearLayout ll = new LinearLayout(this); ll.setOrientation(LinearLayout.VERTICAL); TextView myTextView = new TextView(this); EditText myEditText = new EditText(this); myTextView.setText(“Enter Text Below”); myEditText.setText(“Text Goes Here!”); int lHeight = LinearLayout.LayoutParams.FILL_PARENT; int lWidth = LinearLayout.LayoutParams.WRAP_CONTENT; ll.addView(myTextView, new LinearLayout.LayoutParams(lHeight, lWidth)); ll.addView(myEditText, new LinearLayout.LayoutParams(lHeight, lWidth)); setContentView(ll); Creating New Views The ability to extend existing Views, create composite widgets, and create unique new controls lets you create beautiful User Interfaces optimized for your particular workfl ow. Android lets you subclass the existing widget toolbox and implement your own View controls, giving you total freedom to tailor your User Interface to maximize the user experience.
Chapter 4: Creating User Interfaces When you design a User Interface, it’s important to balance raw aesthetics and usability. With the power to create your own custom controls comes the temptation to rebuild all of them from scratch. Resist that urge. The standard widgets will be familiar to users from other Android applications. On small screens with users often paying limited attention, familiarity can often provide better usability than a slightly shinier widget. Deciding on your approach when creating a new View depends on what you want to achieve: ❑ ❑ ❑ Modify or extend the appearance and/or behavior of an existing control when it already supplies the basic functionality you want. By overriding the event handlers and onDraw, but still calling back to the superclass’s methods, you can customize the control without having to reimplement its functionality. For example, you could customize a TextView to display a set number of decimal points. Combine controls to create atomic, reusable widgets that leverage the functionality of several interconnected controls. For example, you could create a dropdown combo box by combining a TextView and a Button that displays a fl oating ListView when clicked. Create an entirely new control when you need a completely different interface that can’t be achieved by changing or combining existing controls. Modifying Existing Views The toolbox includes a lot of common UI requirements, but the controls are necessarily generic. By customizing these basic Views, you avoid reimplementing existing behavior while still tailoring the User Interface, and functionality, of each control to your application’s needs. To create a new widget based on an existing control, create a new class that extends it — as shown in the following skeleton code that extends TextView: import android.content.Context; import android.util.AttributeSet; import android.widget.TextView; public class MyTextView extends TextView { } public MyTextView (Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); } public MyTextView (Context context) { super(context); } public MyTextView (Context context, AttributeSet attrs) { super(context, attrs); } To override the appearance or behavior of your new View, override and extend the event handlers associated with the behavior you want to change. 81
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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
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Introduction Now is an exciting tim
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Introduction covered, you can move
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Introduction At http://p2p.wrox.com
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Chapter 1: Hello, Android 2 Using t
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Chapter 1: Hello, Android An Open P
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Chapter 1: Hello, Android 6 ❑ ❑
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Chapter 1: Hello, Android 8 When ma
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Chapter 1: Hello, Android 10 In mar
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Chapter 1: Hello, Android 12 Each A
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Chapter 1: Hello, Android 14 ❑ Da
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Chapter 1: Hello, Android 16 ❑ an
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Getting Started All you need to sta
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Chapter 2: Getting Started Unless o
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Installing the ADT Plug-in Install
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Chapter 2: Getting Started 3. In th
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Chapter 2: Getting Started If every
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Data Storage, Retrieval, and Sharin
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Chapter 6: Data Storage, Retrieval,
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} Chapter 6: Data Storage, Retrieva
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} } } Chapter 6: Data Storage, Retr
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Querying Your Database Chapter 6: D
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} // Open or create the database to
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Adding, Updating, and Deleting Cont
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} } Chapter 6: Data Storage, Retrie
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} } break; Chapter 6: Data Storage,
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Maps, Geocoding, and Location-Based
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Chapter 7: Maps, Geocoding, and Loc
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} Chapter 7: Maps, Geocoding, and L
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Summary Chapter 7: Maps, Geocoding,
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Chapter 8: Working in the Backgroun
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Peer-to-Peer Communication In this
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Chapter 9: Peer-to-Peer Communicati
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} Chapter 9: Peer-to-Peer Communica
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Handling Subscription Requests Chap
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Figure 9-4 Chapter 9: Peer-to-Peer
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Accessing Android Hardware Android
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Chapter 10: Accessing Android Hardw
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content.put(Audio.AudioColumns.DATE
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public void onShutter() { // TODO D
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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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404 interapplication communication
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406 passing custom class objects pa
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408 synchronizing threads synchroni
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Programmer to Programmer Get more
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Android™ Application Development - Bahar Ali Khan

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