Android™ Application Development - Bahar Ali Khan

Chapter 11: Advanced Android Development
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}
if (super.onKeyDown(_keyCode, _event))
return true;
if (_event.getAction() == KeyEvent.ACTION_DOWN){
switch (_keyCode) {
case (KeyEvent.KEYCODE_DPAD_LEFT):
movePosition(textPosition, TextPosition.Left); return true;
case (KeyEvent.KEYCODE_DPAD_RIGHT):
movePosition(textPosition, TextPosition.Right); return true;
case (KeyEvent.KEYCODE_DPAD_UP):
movePosition(textPosition, TextPosition.Top); return true;
case (KeyEvent.KEYCODE_DPAD_DOWN):
movePosition(textPosition, TextPosition.Bottom); return true;
}
}
return false;
Running the application now will show a screen displaying “Center”; pressing any of the four directions
will slide out this text and display the appropriate new position.
As an extra step, you could wire up the accelerometer sensor rather than relying on pressing the D-pad.
Animating Layouts and View Groups
A LayoutAnimation is used to animate View Groups, applying a single Animation (or Animation Set)
to each child View in a predetermined sequence.
Use a LayoutAnimationController to specify an Animation (or Animation Set) that’s applied to each
child View in a View Group. Each View it contains will have the same animation applied, but you can
use the Layout Animation Controller to specify the order and start time for each View.
Android includes two LayoutAnimationController classes.
❑ LayoutAnimationController Lets you select the start offset of each View (in milliseconds)
and the order (forward, reverse, and random) to apply the animation to each child View.
❑ GridLayoutAnimationController Is a derived class that lets you assign the animation
sequence of the child Views using grid row and column references.
Creating Layout Animations
To create a new Layout Animation, start by defi ning the Animation to apply to each child view. Then
create a new LayoutAnimation, either in code or as an external animation resource, that references the
animation to apply and defi nes the order and timing in which to apply it.
The following XML snippets show the defi nition of a simple animation stored as popin.xml in the res/
anim folder, and a layout animation stored as popinlayout.xml.
The Layout Animation applies a simple “pop-in” animation randomly to each child View of any View
Group it’s assigned to.