Chapter 2.1 – Animation Resources

An animation resource can define one of two types of animations:

Property Animation

Creates an animation by modifying an object’s property values over a set period of time with an Animator.

View Animation

There are two types of animations that you can do with the view animation framework:

• Tween animation: Creates an animation by performing a series of transformations on a single image with an Animation
• Frame animation: or creates an animation by showing a sequence of images in order with an AnimationDrawable.

Property Animation

An animation defined in XML that modifies properties of the target object, such as background color or alpha value, over a set amount of time.

FILE LOCATION:

res/animator/filename.xml
The filename will be used as the resource ID.

COMPILED RESOURCE DATATYPE:

Resource pointer to a ValueAnimator, ObjectAnimator, or AnimatorSet.

RESOURCE REFERENCE:

In Java: R.animator.filename
In XML: @[package:]animator/filename

SYNTAX:

<set
  android:ordering=["together" | "sequentially"]>
    <objectAnimator
        android:propertyName="string"
        android:duration="int"
        android:valueFrom="float | int | color"
        android:valueTo="float | int | color"
        android:startOffset="int"
        android:repeatCount="int"
        android:repeatMode=["repeat" | "reverse"]
        android:valueType=["intType" | "floatType"]/>
    <animator
        android:duration="int"
        android:valueFrom="float | int | color"
        android:valueTo="float | int | color"
        android:startOffset="int"
        android:repeatCount="int"
        android:repeatMode=["repeat" | "reverse"]
        android:valueType=["intType" | "floatType"]/>
    <set>
        ...
    </set>
</set>

The file must have a single root element: either <set>, <objectAnimator>, or <valueAnimator>. You can group animation elements together inside the <set> element, including other <set> elements.

ELEMENTS:

<set>

A container that holds other animation elements (<objectAnimator>, <valueAnimator>, or other <set> elements). Represents an AnimatorSet. You can specify nested <set> tags to further group animations together. Each <set> can define its own ordering attribute.

attributes:

android:ordering

Keyword. Specifies the play ordering of animations in this set.

Value	Description
sequentially	Play animations in this set sequentially
together (default)	Play animations in this set at the same time.

<objectAnimator>

Animates a specific property of an object over a specific amount of time. Represents an ObjectAnimator.

attributes:

android:propertyName

String. Required. The object’s property to animate, referenced by its name. For example you can specify "alpha" or"backgroundColor" for a View object. The objectAnimator element does not expose a target attribute, however, so you cannot set the object to animate in the XML declaration. You have to inflate your animation XML resource by calling loadAnimator() and call setTarget() to set the target object that contains this property.

android:valueTo

float, int, or color. Required. The value where the animated property ends. Colors are represented as six digit hexadecimal numbers (for example, #333333).

android:valueFrom

float, int, or color. The value where the animated property starts. If not specified, the animation starts at the value obtained by the property’s get method. Colors are represented as six digit hexadecimal numbers (for example, #333333).

android:duration

int. The time in milliseconds of the animation. 300 milliseconds is the default.

android:startOffset

int. The amount of milliseconds the animation delays after start() is called.

android:repeatCount

int. How many times to repeat an animation. Set to "-1" to infinitely repeat or to a positive integer. For example, a value of "1"means that the animation is repeated once after the initial run of the animation, so the animation plays a total of two times. The default value is "0", which means no repetition.

android:repeatMode

int. How an animation behaves when it reaches the end of the animation. android:repeatCount must be set to a positive integer or"-1" for this attribute to have an effect. Set to "reverse" to have the animation reverse direction with each iteration or "repeat" to have the animation loop from the beginning each time.

android:valueType

Keyword. Do not specify this attribute if the value is a color. The animation framework automatically handles color values

Value	Description
intType	Specifies that the animated values are integers
floatType (default)	Specifies that the animated values are floats

<animator>

Performs an animation over a specified amount of time. Represents a ValueAnimator.

attributes:

android:valueTo

float, int, or color. Required. The value where the animation ends. Colors are represented as six digit hexadecimal numbers (for example, #333333).

android:valueFrom

float, int, or color. Required. The value where the animation starts. Colors are represented as six digit hexadecimal numbers (for example, #333333).

android:duration

int. The time in milliseconds of the animation. 300ms is the default.

android:startOffset

int. The amount of milliseconds the animation delays after start() is called.

android:repeatCount

int. How many times to repeat an animation. Set to "-1" to infinitely repeat or to a positive integer. For example, a value of "1"means that the animation is repeated once after the initial run of the animation, so the animation plays a total of two times. The default value is "0", which means no repetition.

android:repeatMode

int. How an animation behaves when it reaches the end of the animation. android:repeatCount must be set to a positive integer or"-1" for this attribute to have an effect. Set to "reverse" to have the animation reverse direction with each iteration or "repeat" to have the animation loop from the beginning each time.

android:valueType

Keyword. Do not specify this attribute if the value is a color. The animation framework automatically handles color values.

Value	Description
intType	Specifies that the animated values are integers
floatType (default)	Specifies that the animated values are floats

EXAMPLE:

XML file saved at res/animator/property_animator.xml:

<set android:ordering="sequentially">
    <set>
        <objectAnimator
            android:propertyName="x"
            android:duration="500"
            android:valueTo="400"
            android:valueType="intType"/>
        <objectAnimator
            android:propertyName="y"
            android:duration="500"
            android:valueTo="300"
            android:valueType="intType"/>
    </set>
    <objectAnimator
        android:propertyName="alpha"
        android:duration="500"
        android:valueTo="1f"/>
</set>

In order to run this animation, you must inflate the XML resources in your code to an AnimatorSet object, and then set the target objects for all of the animations before starting the animation set. Calling setTarget() sets a single target object for all children of the AnimatorSet as a convenience. The following code shows how to do this:

AnimatorSet set = (AnimatorSet) AnimatorInflater.loadAnimator(myContext,
    R.anim.property_animator);
set.setTarget(myObject);
set.start();

SEE ALSO:

• Property Animation
• API Demos for examples on how to use the property animation system.

View Animation

The view animation framework supports both tween and frame by frame animations, which can both be declared in XML. The following sections describe how to use both methods.

Tween animation

An animation defined in XML that performs transitions such as rotating, fading, moving, and stretching on a graphic.

FILE LOCATION:

res/anim/filename.xml
The filename will be used as the resource ID.

COMPILED RESOURCE DATATYPE:

Resource pointer to an Animation.

RESOURCE REFERENCE:

In Java: R.anim.filename
In XML: @[package:]anim/filename

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:interpolator="@[package:]anim/interpolator_resource"
    android:shareInterpolator=["true" | "false"] >
    <alpha
        android:fromAlpha="float"
        android:toAlpha="float" />
    <scale
        android:fromXScale="float"
        android:toXScale="float"
        android:fromYScale="float"
        android:toYScale="float"
        android:pivotX="float"
        android:pivotY="float" />
    <translate
        android:fromXDelta="float"
        android:toXDelta="float"
        android:fromYDelta="float"
        android:toYDelta="float" />
    <rotate
        android:fromDegrees="float"
        android:toDegrees="float"
        android:pivotX="float"
        android:pivotY="float" />
    <set>
        ...
    </set>
</set>

The file must have a single root element: either an <alpha>, <scale>, <translate>, <rotate>, or <set> element that holds a group (or groups) of other animation elements (even nested <set> elements).

ELEMENTS:

<set>

A container that holds other animation elements (<alpha>, <scale>, <translate>, <rotate>) or other <set> elements. Represents an AnimationSet.

attributes:

android:interpolator

Interpolator resource. An Interpolator to apply on the animation. The value must be a reference to a resource that specifies an interpolator (not an interpolator class name). There are default interpolator resources available from the platform or you can create your own interpolator resource. See the discussion below for more about Interpolators.

android:shareInterpolator

Boolean. “true” if you want to share the same interpolator among all child elements.

<alpha>

A fade-in or fade-out animation. Represents an AlphaAnimation.

attributes:

android:fromAlpha

Float. Starting opacity offset, where 0.0 is transparent and 1.0 is opaque.

android:toAlpha

Float. Ending opacity offset, where 0.0 is transparent and 1.0 is opaque.

For more attributes supported by <alpha>, see the Animation class reference (of which, all XML attributes are inherrited by this element).

<scale>

A resizing animation. You can specify the center point of the image from which it grows outward (or inward) by specifying pivotX andpivotY. For example, if these values are 0, 0 (top-left corner), all growth will be down and to the right. Represents a ScaleAnimation.

attributes:

android:fromXScale

Float. Starting X size offset, where 1.0 is no change.

android:toXScale

Float. Ending X size offset, where 1.0 is no change.

android:fromYScale

Float. Starting Y size offset, where 1.0 is no change.

android:toYScale

Float. Ending Y size offset, where 1.0 is no change.

android:pivotX

Float. The X coordinate to remain fixed when the object is scaled.

android:pivotY

Float. The Y coordinate to remain fixed when the object is scaled.

For more attributes supported by <scale>, see the Animation class reference (of which, all XML attributes are inherrited by this element).

<translate>

A vertical and/or horizontal motion. Supports the following attributes in any of the following three formats: values from -100 to 100 ending with “%”, indicating a percentage relative to itself; values from -100 to 100 ending in “%p”, indicating a percentage relative to its parent; a float value with no suffix, indicating an absolute value. Represents a TranslateAnimation.

attributes:

android:fromXDelta

Float or percentage. Starting X offset. Expressed either: in pixels relative to the normal position (such as "5"), in percentage relative to the element width (such as "5%"), or in percentage relative to the parent width (such as "5%p").

android:toXDelta

Float or percentage. Ending X offset. Expressed either: in pixels relative to the normal position (such as "5"), in percentage relative to the element width (such as "5%"), or in percentage relative to the parent width (such as "5%p").

android:fromYDelta

Float or percentage. Starting Y offset. Expressed either: in pixels relative to the normal position (such as "5"), in percentage relative to the element height (such as "5%"), or in percentage relative to the parent height (such as "5%p").

android:toYDelta

Float or percentage. Ending Y offset. Expressed either: in pixels relative to the normal position (such as "5"), in percentage relative to the element height (such as "5%"), or in percentage relative to the parent height (such as "5%p").

For more attributes supported by <translate>, see the Animation class reference (of which, all XML attributes are inherrited by this element).

<rotate>

A rotation animation. Represents a RotateAnimation.

attributes:

android:fromDegrees

Float. Starting angular position, in degrees.

android:toDegrees

Float. Ending angular position, in degrees.

android:pivotX

Float or percentage. The X coordinate of the center of rotation. Expressed either: in pixels relative to the object’s left edge (such as"5"), in percentage relative to the object’s left edge (such as "5%"), or in percentage relative to the parent container’s left edge (such as "5%p").

android:pivotY

Float or percentage. The Y coordinate of the center of rotation. Expressed either: in pixels relative to the object’s top edge (such as"5"), in percentage relative to the object’s top edge (such as "5%"), or in percentage relative to the parent container’s top edge (such as "5%p").

For more attributes supported by <rotate>, see the Animation class reference (of which, all XML attributes are inherrited by this element).

EXAMPLE:

XML file saved at res/anim/hyperspace_jump.xml:

<set xmlns:android="http://schemas.android.com/apk/res/android"
    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/accelerate_interpolator"
        android:startOffset="700">
        <scale
            android:fromXScale="1.4"
            android:toXScale="0.0"
            android:fromYScale="0.6"
            android:toYScale="0.0"
            android:pivotX="50%"
            android:pivotY="50%"
            android:duration="400" />
        <rotate
            android:fromDegrees="0"
            android:toDegrees="-45"
            android:toYScale="0.0"
            android:pivotX="50%"
            android:pivotY="50%"
            android:duration="400" />
    </set>
</set>

This application code will apply the animation to an ImageView and start the animation:

ImageView image = (ImageView) findViewById(R.id.image);
Animation hyperspaceJump = AnimationUtils.loadAnimation(this, R.anim.hyperspace_jump); image.startAnimation(hyperspaceJump);

SEE ALSO:

• 2D Graphics: Tween Animation

Interpolators

An interpolator is an animation modifier defined in XML that affects the rate of change in an animation. This allows your existing animation effects to be accelerated, decelerated, repeated, bounced, etc.
An interpolator is applied to an animation element with the android:interpolator attribute, the value of which is a reference to an interpolator resource.
All interpolators available in Android are subclasses of the Interpolator class. For each interpolator class, Android includes a public resource you can reference in order to apply the interpolator to an animation using the android:interpolator attribute. The following table specifies the resource to use for each interpolator:

Interpolator class	Resource ID
AccelerateDecelerateInterpolator	@android:anim/accelerate_decelerate_interpolator
AccelerateInterpolator	@android:anim/accelerate_interpolator
AnticipateInterpolator	@android:anim/anticipate_interpolator
AnticipateOvershootInterpolator	@android:anim/anticipate_overshoot_interpolator
BounceInterpolator	@android:anim/bounce_interpolator
CycleInterpolator	@android:anim/cycle_interpolator
DecelerateInterpolator	@android:anim/decelerate_interpolator
LinearInterpolator	@android:anim/linear_interpolator
OvershootInterpolator	@android:anim/overshoot_interpolator

Here’s how you can apply one of these with the android:interpolator attribute:

<set android:interpolator="@android:anim/accelerate_interpolator">
    ...
</set>

Custom interpolators

If you’re not satisfied with the interpolators provided by the platform (listed in the table above), you can create a custom interpolator resource with modified attributes. For example, you can adjust the rate of acceleration for the AnticipateInterpolator, or adjust the number of cycles for the CycleInterpolator. In order to do so, you need to create your own interpolator resource in an XML file.

FILE LOCATION:

res/anim/filename.xml
The filename will be used as the resource ID.

COMPILED RESOURCE DATATYPE:

Resource pointer to the corresponding interpolator object.

RESOURCE REFERENCE:

In XML: @[package:]anim/filename

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<InterpolatorName xmlns:android="http://schemas.android.com/apk/res/android"
    android:attribute_name="value"
    />

If you don’t apply any attributes, then your interpolator will function exactly the same as those provided by the platform (listed in the table above).

ELEMENTS:

Notice that each Interpolator implementation, when defined in XML, begins its name in lowercase.

<accelerateDecelerateInterpolator>

The rate of change starts and ends slowly but accelerates through the middle.No attributes.

<accelerateInterpolator>

The rate of change starts out slowly, then accelerates.

attributes:

android:factor

Float. The acceleration rate (default is 1).

<anticipateInterpolator>

The change starts backward then flings forward.

attributes:

android:tension

Float. The amount of tension to apply (default is 2).

<anticipateOvershootInterpolator>

The change starts backward, flings forward and overshoots the target value, then settles at the final value.

attributes:

android:tension

Float. The amount of tension to apply (default is 2).

android:extraTension

Float. The amount by which to multiply the tension (default is 1.5).

<bounceInterpolator>

The change bounces at the end.No attributes

<cycleInterpolator>

Repeats the animation for a specified number of cycles. The rate of change follows a sinusoidal pattern.

attributes:

android:cycles

Integer. The number of cycles (default is 1).

<decelerateInterpolator>

The rate of change starts out quickly, then decelerates.

attributes:

android:factor

Float. The deceleration rate (default is 1).

<linearInterpolator>

The rate of change is constant.No attributes.

<overshootInterpolator>

The change flings forward and overshoots the last value, then comes back.

attributes:

android:tension

Float. The amount of tension to apply (default is 2).

EXAMPLE:

XML file saved at res/anim/my_overshoot_interpolator.xml:

<?xml version="1.0" encoding="utf-8"?>
<overshootInterpolator xmlns:android="http://schemas.android.com/apk/res/android"
    android:tension="7.0"
    />

This animation XML will apply the interpolator:

<scale xmlns:android="http://schemas.android.com/apk/res/android"
    android:interpolator="@anim/my_overshoot_interpolator"
    android:fromXScale="1.0"
    android:toXScale="3.0"
    android:fromYScale="1.0"
    android:toYScale="3.0"
    android:pivotX="50%"
    android:pivotY="50%"
    android:duration="700" />

Frame animation

An animation defined in XML that shows a sequence of images in order (like a film).

FILE LOCATION:

res/drawable/filename.xml
The filename will be used as the resource ID.

COMPILED RESOURCE DATATYPE:

Resource pointer to an AnimationDrawable.

RESOURCE REFERENCE:

In Java: R.drawable.filename
In XML: @[package:]drawable.filename

SYNTAX:

<?xml version="1.0" encoding="utf-8"?>
<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
    android:oneshot=["true" | "false"] >
    <item
        android:drawable="@[package:]drawable/drawable_resource_name"
        android:duration="integer" />
</animation-list>

ELEMENTS:

<animation-list>

Required. This must be the root element. Contains one or more <item> elements.

attributes:

android:oneshot

Boolean. “true” if you want to perform the animation once; “false” to loop the animation.

<item>

A single frame of animation. Must be a child of a <animation-list> element.

attributes:

android:drawable

Drawable resource. The drawable to use for this frame.

android:duration

Integer. The duration to show this frame, in milliseconds.

EXAMPLE:

XML file saved at res/anim/rocket.xml:

<?xml version="1.0" encoding="utf-8"?>
<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
    android:oneshot="false">
    <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 application code will set the animation as the background for a View, then play the animation:

ImageView rocketImage = (ImageView) findViewById(R.id.rocket_image);
rocketImage.setBackgroundResource(R.drawable.rocket_thrust); rocketAnimation = (AnimationDrawable) rocketImage.getBackground(); rocketAnimation.start();