Drawable animation lets you load a series of Drawable resources one after another to create an animation. This is a traditional animation in the sense that it is created with a sequence of different images, played in order, like a roll of film. The {@link android.graphics.drawable.AnimationDrawable} class is the basis for Drawable animations.
While you can define the frames of an animation in your code, using the {@link
android.graphics.drawable.AnimationDrawable} class API, it's more simply accomplished with a
single XML file that lists the frames that compose the animation. The XML file for this kind
of animation belongs in the res/drawable/ directory of
your Android project. In this case, the instructions are the order and duration for each frame of
the animation.
The XML file consists of an <animation-list> element as the root node and a
series of child <item> nodes that each define a frame: a drawable resource for
the frame and the frame duration. Here's an example XML file for a Drawable animation:
<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
android:oneshot="true">
<item android:drawable="@drawable/rocket_thrust1" android:duration="200" />
<item android:drawable="@drawable/rocket_thrust2" android:duration="200" />
<item android:drawable="@drawable/rocket_thrust3" android:duration="200" />
</animation-list>
This animation runs for just three frames. By setting the android:oneshot
attribute of the list to true, it will cycle just once then stop and hold on the last
frame. If it is set false then the animation will loop. With this XML saved as
rocket_thrust.xml in the res/drawable/ directory of the project, it can
be added as the background image to a View and then called to play. Here's an example Activity,
in which the animation is added to an {@link android.widget.ImageView} and then animated when the
screen is touched:
AnimationDrawable rocketAnimation;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ImageView rocketImage = (ImageView) findViewById(R.id.rocket_image);
rocketImage.setBackgroundResource(R.drawable.rocket_thrust);
rocketAnimation = (AnimationDrawable) rocketImage.getBackground();
}
public boolean onTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN) {
rocketAnimation.start();
return true;
}
return super.onTouchEvent(event);
}
It's important to note that the start() method called on the AnimationDrawable
cannot be called during the onCreate() method of your Activity, because the
AnimationDrawable is not yet fully attached to the window. If you want to play the animation
immediately, without requiring interaction, then you might want to call it from the {@link
android.app.Activity#onWindowFocusChanged(boolean) onWindowFocusChanged()} method in your
Activity, which will get called when Android brings your window into focus.
For more information on the XML syntax, available tags and attributes, see Animation Resources.