android_frameworks_base/docs/html/guide/topics/graphics/view-animation.jd

page.title=View Animation
parent.title=Graphics
parent.link=index.html
@jd:body

  <div id="qv-wrapper">
    <div id="qv">
      <h2>In this document</h2>

      <ol>       
       <li><a href="#tween-animation">Tween animation</a></li>
       <li><a href="#frame-animation">Frame animation</a></li>
     </ol>

    </div>
  </div>

  You can use View Animation in any View object to
  perform tweened animation and frame by frame animation. Tween animation calculates the animation
  given information such as the start point, end point, size, rotation, and other common aspects of
  an animation. Frame by frame animation lets you load a series of Drawable resources one after
  another to create an animation.

  <h2 id="tween-animation">Tween Animation</h2>

  <p>A tween animation can perform a series of simple transformations (position, size, rotation,
  and transparency) on the contents of a View object. So, if you have a {@link
  android.widget.TextView} object, you can move, rotate, grow, or shrink the text. If it has a
  background image, the background image will be transformed along with the text. The {@link
  android.view.animation animation package} provides all the classes used in a tween animation.</p>

  <p>A sequence of animation instructions defines the tween animation, defined by either XML or
  Android code. As with defining a layout, an XML file is recommended because it's more readable,
  reusable, and swappable than hard-coding the animation. In the example below, we use XML. (To
  learn more about defining an animation in your application code, instead of XML, refer to the
  {@link android.view.animation.AnimationSet} class and other {@link
  android.view.animation.Animation} subclasses.)</p>

  <p>The animation instructions define the transformations that you want to occur, when they will
  occur, and how long they should take to apply. Transformations can be sequential or simultaneous
  - for example, you can have the contents of a TextView move from left to right, and then rotate
  180 degrees, or you can have the text move and rotate simultaneously. Each transformation takes a
  set of parameters specific for that transformation (starting size and ending size for size
  change, starting angle and ending angle for rotation, and so on), and also a set of common
  parameters (for instance, start time and duration). To make several transformations happen
  simultaneously, give them the same start time; to make them sequential, calculate the start time
  plus the duration of the preceding transformation.</p>

  <p>The animation XML file belongs in the <code>res/anim/</code> directory of your Android
  project. The file must have a single root element: this will be either a single
  <code>&lt;alpha&gt;</code>, <code>&lt;scale&gt;</code>, <code>&lt;translate&gt;</code>,
  <code>&lt;rotate&gt;</code>, interpolator element, or <code>&lt;set&gt;</code> element that holds
  groups of these elements (which may include another <code>&lt;set&gt;</code>). By default, all
  animation instructions are applied simultaneously. To make them occur sequentially, you must
  specify the <code>startOffset</code> attribute, as shown in the example below.</p>

  <p>The following XML from one of the ApiDemos is used to stretch, then simultaneously spin and
  rotate a View object.</p>
  <pre>
&lt;set android:shareInterpolator="false"&gt;
    &lt;scale
        android:interpolator="@android:anim/accelerate_decelerate_interpolator"
        android:fromXScale="1.0"
        android:toXScale="1.4"
        android:fromYScale="1.0"
        android:toYScale="0.6"
        android:pivotX="50%"
        android:pivotY="50%"
        android:fillAfter="false"
        android:duration="700" /&gt;
    &lt;set android:interpolator="@android:anim/decelerate_interpolator"&gt;
        &lt;scale
           android:fromXScale="1.4"
           android:toXScale="0.0"
           android:fromYScale="0.6"
           android:toYScale="0.0"
           android:pivotX="50%"
           android:pivotY="50%"
           android:startOffset="700"
           android:duration="400"
           android:fillBefore="false" /&gt;
        &lt;rotate
           android:fromDegrees="0"
           android:toDegrees="-45"
           android:toYScale="0.0"
           android:pivotX="50%"
           android:pivotY="50%"
           android:startOffset="700"
           android:duration="400" /&gt;
    &lt;/set&gt;
&lt;/set&gt;
</pre>

  <p>Screen coordinates (not used in this example) are (0,0) at the upper left hand corner, and
  increase as you go down and to the right.</p>

  <p>Some values, such as pivotX, can be specified relative to the object itself or relative to the
  parent. Be sure to use the proper format for what you want ("50" for 50% relative to the parent,
  or "50%" for 50% relative to itself).</p>

  <p>You can determine how a transformation is applied over time by assigning an {@link
  android.view.animation.Interpolator}. Android includes several Interpolator subclasses that
  specify various speed curves: for instance, {@link android.view.animation.AccelerateInterpolator}
  tells a transformation to start slow and speed up. Each one has an attribute value that can be
  applied in the XML.</p>

  <p>With this XML saved as <code>hyperspace_jump.xml</code> in the <code>res/anim/</code>
  directory of the project, the following code will reference it and apply it to an {@link
  android.widget.ImageView} object from the layout.</p>
  <pre>
ImageView spaceshipImage = (ImageView) findViewById(R.id.spaceshipImage);
Animation hyperspaceJumpAnimation = AnimationUtils.loadAnimation(this, R.anim.hyperspace_jump);
spaceshipImage.startAnimation(hyperspaceJumpAnimation);
</pre>

  <p>As an alternative to <code>startAnimation()</code>, you can define a starting time for the
  animation with <code>{@link android.view.animation.Animation#setStartTime(long)
  Animation.setStartTime()}</code>, then assign the animation to the View with <code>{@link
  android.view.View#setAnimation(android.view.animation.Animation) View.setAnimation()}</code>.</p>

  <p>For more information on the XML syntax, available tags and attributes, see <a href=
  "{@docRoot}guide/topics/resources/animation-resource.html">Animation Resources</a>.</p>

  <p class="note"><strong>Note:</strong> Regardless of how your animation may move or resize, the
  bounds of the View that holds your animation will not automatically adjust to accommodate it.
  Even so, the animation will still be drawn beyond the bounds of its View and will not be clipped.
  However, clipping <em>will occur</em> if the animation exceeds the bounds of the parent View.</p>

  <h2 id="frame-animation">Frame Animation</h2>

  <p>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 frame animations.</p>

  <p>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. Like the tween animation above,
  the XML file for this kind of animation belongs in the <code>res/drawable/</code> directory of
  your Android project. In this case, the instructions are the order and duration for each frame of
  the animation.</p>

  <p>The XML file consists of an <code>&lt;animation-list&gt;</code> element as the root node and a
  series of child <code>&lt;item&gt;</code> nodes that each define a frame: a drawable resource for
  the frame and the frame duration. Here's an example XML file for a frame-by-frame animation:</p>
  <pre>
&lt;animation-list xmlns:android="http://schemas.android.com/apk/res/android"
    android:oneshot="true"&gt;
    &lt;item android:drawable="@drawable/rocket_thrust1" android:duration="200" /&gt;
    &lt;item android:drawable="@drawable/rocket_thrust2" android:duration="200" /&gt;
    &lt;item android:drawable="@drawable/rocket_thrust3" android:duration="200" /&gt;
&lt;/animation-list&gt;
</pre>

  <p>This animation runs for just three frames. By setting the <code>android:oneshot</code>
  attribute of the list to <var>true</var>, it will cycle just once then stop and hold on the last
  frame. If it is set <var>false</var> then the animation will loop. With this XML saved as
  <code>rocket_thrust.xml</code> in the <code>res/drawable/</code> 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:</p>
  <pre>
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);
}
</pre>

  <p>It's important to note that the <code>start()</code> method called on the AnimationDrawable
  cannot be called during the <code>onCreate()</code> 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 <code>{@link
  android.app.Activity#onWindowFocusChanged(boolean) onWindowFocusChanged()}</code> method in your
  Activity, which will get called when Android brings your window into focus.</p>

  <p>For more information on the XML syntax, available tags and attributes, see <a href=
  "{@docRoot}guide/topics/resources/animation-resource.html">Animation Resources</a>.</p>
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