page.title=View Animation
parent.title=Animation
parent.link=animation.html
@jd:body
<p>You can use the view animation system to perform tweened animation on Views. Tween animation
calculates the animation with information such as the start point, end point, size, rotation, and
other common aspects of an animation.
</p>
<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><alpha></code>, <code><scale></code>, <code><translate></code>,
<code><rotate></code>, interpolator element, or <code><set></code> element that holds
groups of these elements (which may include another <code><set></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>
<set android:shareInterpolator="false">
<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" />
<set android:interpolator="@android:anim/decelerate_interpolator">
<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" />
<rotate
android:fromDegrees="0"
android:toDegrees="-45"
android:toYScale="0.0"
android:pivotX="50%"
android:pivotY="50%"
android:startOffset="700"
android:duration="400" />
</set>
</set>
</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>