Beginning Android

 public void onCreate(Bundle icicle) {
  super.onCreate(icicle);
  setContentView(R.layout.main);
  flipper = (ViewFlipper)findViewById(R.id.details);
  Button btn = (Button)findViewById(R.id.flip_me);
  btn.setOnClickListener(new View.OnClickListener() {
   public void onClick(View view) {
    flipper.showNext();
   }
  });
 }
}

This is just a matter of calling showNext() on the ViewFlipper, like you can on any ViewAnimator class.

The result is a trivial activity: click the button, and the next TextView in sequence is displayed, wrapping around to the first after viewing the last (see Figures 10-9 and 10-10).

Figure 10-9. The Flipper1 application, showing the first panel

Figure 10-10. The same application, after switching to the second panel

This, of course, could be handled more simply by having a single TextView and changing the text and color on each click. However, you can imagine that the ViewFlipper contents could be much more complicated, like the contents you might put into a TabView.

As with the TabWidget, sometimes, your ViewFlipper contents may not be known at compile time. As with TabWidget, though, you can add new contents on the fly with ease.

For example, let’s look at another sample activity (Fancy/Flipper2), using this layout:

<?xml version='1.0' encoding='utf-8'?>
<LinearLayout xmlns:android='http://schemas.android.com/apk/res/android'
 android:orientation='vertical'
 android:layout_width='fill_parent'
 android:layout_height='fill_parent'
>
 <ViewFlipper android:id='@+id/details'
  android:layout_width='fill_parent'
  android:layout_height='fill_parent'
 >
 </ViewFlipper>
</LinearLayout>

Notice that the ViewFlipper has no contents at compile time. Also note that there is no Button for flipping between the contents — more on this in a moment.

For the ViewFlipper contents, we will create large Button widgets, each containing one of a set of random words. And, we will set up the ViewFlipper to automatically rotate between the Button widgets, using an animation for transition:

public class FlipperDemo2 extends Activity {
 static String[] items={'lorem', 'ipsum', 'dolor', 'sit', 'amet',
  'consectetuer', 'adipiscing', 'elit',
  'morbi', 'vel', 'ligula', 'vitae',
  'arcu', 'aliquet', 'mollis', 'etiam',
  'vel', 'erat', 'placerat', 'ante',
  'porttitor', 'sodales', 'pellentesque',
  'augue', 'purus'};
 ViewFlipper flipper;
 @Override
 public void onCreate(Bundle icicle) {
  super.onCreate(icicle);
  setContentView(R.layout.main);
  flipper = (ViewFlipper)findViewById(R.id.details);
  flipper.setInAnimation(AnimationUtils.loadAnimation (this,
   R.anim.push_left_in));
  flipper.setOutAnimation(AnimationUtils.loadAnimation (this,
   R.anim.push_left_out));
  for (String item : items) {
   Button btn = new Button(this);
   btn.setText(item);
   flipper.addView(btn,
    new ViewGroup.LayoutParams(
     ViewGroup.LayoutParams.FILL_PARENT,
     ViewGroup.LayoutParams.FILL_PARENT));
  }
  flipper.setFlipInterval(2000);
  flipper.startFlipping();
 }
}

After getting our ViewFlipper widget from the layout, we first set up the “in” and “out” animations. In Android terms, an animation is a description of how a widget leaves (”out”) or enters (”in”) the viewable area. Animations are a complex beast, eventually worthy of their own chapter but not covered in this text. For now, realize that animations are resources, stored in res/anim/ in your project. For this example, we are using a pair of animations supplied by the SDK samples, available under the Apache 2.0 License. As their names suggest, widgets are “pushed” to the left, either to enter or leave the viewable area.

After iterating over the funky words, turning each into a Button, and adding the Button as a child of the ViewFlipper, we set up the flipper to automatically flip between children (flipper.setFlipInterval(2000);) and to start flipping (flipper.startFlipping ();).

The result is an endless series of buttons, each appearing, then sliding out to the left after 2 seconds, being replaced by the next button in sequence, wrapping around to the first after the last has been shown (see Figure 10