Property Animation Overview

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The property animation system is a robust framework that allows you to animate almost anything. You can define an animation to change any object property over time, regardless of whether it draws to the screen or not. A property animation changes a property's (a field in an object) value over a specified length of time. To animate something, you specify the object property that you want to animate, such as an object's position on the screen, how long you want to animate it for, and what values you want to animate between.

The property animation system lets you define the following characteristics of an animation:

• Duration: You can specify the duration of an animation. The default length is 300 ms.
• Time interpolation: You can specify how the values for the property are calculated as a function of the animation's current elapsed time.
• Repeat count and behavior: You can specify whether or not to have an animation repeat when it reaches the end of a duration and how many times to repeat the animation. You can also specify whether you want the animation to play back in reverse. Setting it to reverse plays the animation forwards then backwards repeatedly, until the number of repeats is reached.
• Animator sets: You can group animations into logical sets that play together or sequentially or after specified delays.
• Frame refresh delay: You can specify how often to refresh frames of your animation. The default is set to refresh every 10 ms, but the speed in which your application can refresh frames is ultimately dependent on how busy the system is overall and how fast the system can service the underlying timer.

To see a full example of property animation, see the ChangeColor class in the CustomTransition sample on GitHub.

How property animation works

First, let's go over how an animation works with a simple example. Figure 1 depicts a hypothetical object that is animated with its x property, which represents its horizontal location on a screen. The duration of the animation is set to 40 ms and the distance to travel is 40 pixels. Every 10 ms, which is the default frame refresh rate, the object moves horizontally by 10 pixels. At the end of 40ms, the animation stops, and the object ends at horizontal position 40. This is an example of an animation with linear interpolation, meaning the object moves at a constant speed.

Figure 1. Example of a linear animation

You can also specify animations to have a non-linear interpolation. Figure 2 illustrates a hypothetical object that accelerates at the beginning of the animation, and decelerates at the end of the animation. The object still moves 40 pixels in 40 ms, but non-linearly. In the beginning, this animation accelerates up to the halfway point then decelerates from the halfway point until the end of the animation. As Figure 2 shows, the distance traveled at the beginning and end of the animation is less than in the middle.

Figure 2. Example of a non-linear animation

Let's take a detailed look at how the important components of the property animation system would calculate animations like the ones illustrated above. Figure 3 depicts how the main classes work with one another.

Figure 3. How animations are calculated

The ValueAnimator object keeps track of your animation's timing, such as how long the animation has been running, and the current value of the property that it is animating.

The ValueAnimator encapsulates a TimeInterpolator, which defines animation interpolation, and a TypeEvaluator, which defines how to calculate values for the property being animated. For example, in Figure 2, the TimeInterpolator used would be AccelerateDecelerateInterpolator and the TypeEvaluator would be IntEvaluator.

To start an animation, create a ValueAnimator and give it the starting and ending values for the property that you want to animate, along with the duration of the animation. When you call start() the animation begins. During the whole animation, the ValueAnimator calculates an elapsed fraction between 0 and 1, based on the duration of the animation and how much time has elapsed. The elapsed fraction represents the percentage of time that the animation has completed, 0 meaning 0% and 1 meaning 100%. For example, in Figure 1, the elapsed fraction at t = 10 ms would be .25 because the total duration is t = 40 ms.

When the ValueAnimator is done calculating an elapsed fraction, it calls the TimeInterpolator that is currently set, to calculate an interpolated fraction. An interpolated fraction maps the elapsed fraction to a new fraction that takes into account the time interpolation that is set. For example, in Figure 2, because the animation slowly accelerates, the interpolated fraction, about .15, is less than the elapsed fraction, .25, at t = 10 ms. In Figure 1, the interpolated fraction is always the same as the elapsed fraction.

When the interpolated fraction is calculated, ValueAnimator calls the appropriate TypeEvaluator, to calculate the value of the property that you are animating, based on the interpolated fraction, the starting value, and the ending value of the animation. For example, in Figure 2, the interpolated fraction was .15 at t = 10 ms, so the value for the property at that time would be .15 × (40 - 0), or 6.

How property animation differs from view animation

The view animation system provides the capability to only animate View objects, so if you wanted to animate non-View objects, you have to implement your own code to do so. The view animation system is also constrained in the fact that it only exposes a few aspects of a View object to animate, such as the scaling and rotation of a View but not the background color, for instance.

Another disadvantage of the view animation system is that it only modified where the View was drawn, and not the actual View itself. For instance, if you animated a button to move across the screen, the button draws correctly, but the actual location where you can click the button does not change, so you have to implement your own logic to handle this.

With the property animation system, these constraints are completely removed, and you can animate any property of any object (Views and non-Views) and the object itself is actually modified. The property animation system is also more robust in the way it carries out animation. At a high level, you assign animators to the properties that you want to animate, such as color, position, or size and can define aspects of the animation such as interpolation and synchronization of multiple animators.

The view animation system, however, takes less time to setup and requires less code to write. If view animation accomplishes everything that you need to do, or if your existing code already works the way you want, there is no need to use the property animation system. It also might make sense to use both animation systems for different situations if the use case arises.

API overview

You can find most of the property animation system's APIs in android.animation. Because the view animation system already defines many interpolators in android.view.animation, you can use those interpolators in the property animation system as well. The following tables describe the main components of the property animation system.

The Animator class provides the basic structure for creating animations. You normally do not use this class directly as it only provides minimal functionality that must be extended to fully support animating values. The following subclasses extend Animator:

Table 1. Animators

Evaluators tell the property animation system how to calculate values for a given property. They take the timing data that is provided by an Animator class, the animation's start and end value, and calculate the animated values of the property based on this data. The property animation system provides the following evaluators:

Table 2. Evaluators

A time interpolator defines how specific values in an animation are calculated as a function of time. For example, you can specify animations to happen linearly across the whole animation, meaning the animation moves evenly the entire time, or you can specify animations to use non-linear time, for example, accelerating at the beginning and decelerating at the end of the animation. Table 3 describes the interpolators that are contained in android.view.animation. If none of the provided interpolators suits your needs, implement the TimeInterpolator interface and create your own. See Using interpolators for more information on how to write a custom interpolator.

Table 3. Interpolators

Animate using ValueAnimator

The ValueAnimator class lets you animate values of some type for the duration of an animation by specifying a set of int, float, or color values to animate through. You obtain a ValueAnimator by calling one of its factory methods: ofInt(), ofFloat(), or ofObject(). For example:

ValueAnimator.ofFloat(0f, 100f).apply {
    duration = 1000
    start()
}

ValueAnimator animation = ValueAnimator.ofFloat(0f, 100f);
animation.setDuration(1000);
animation.start();

In this code, the ValueAnimator starts calculating the values of the animation, between 0 and 100, for a duration of 1000 ms, when the start() method runs.

You can also specify a custom type to animate by doing the following:

ValueAnimator.ofObject(MyTypeEvaluator(), startPropertyValue, endPropertyValue).apply {
    duration = 1000
    start()
}

ValueAnimator animation = ValueAnimator.ofObject(new MyTypeEvaluator(), startPropertyValue, endPropertyValue);
animation.setDuration(1000);
animation.start();

In this code, the ValueAnimator starts calculating the values of the animation, between startPropertyValue and endPropertyValue using the logic supplied by MyTypeEvaluator for a duration of 1000 ms, when the start() method runs.

You can use the values of the animation by adding an AnimatorUpdateListener to the ValueAnimator object, as shown in the following code:

ValueAnimator.ofObject(...).apply {
    ...
    addUpdateListener { updatedAnimation ->
        // You can use the animated value in a property that uses the
        // same type as the animation. In this case, you can use the
        // float value in the translationX property.
        textView.translationX = updatedAnimation.animatedValue as Float
    }
    ...
}

animation.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
    @Override
    public void onAnimationUpdate(ValueAnimator updatedAnimation) {
        // You can use the animated value in a property that uses the
        // same type as the animation. In this case, you can use the
        // float value in the translationX property.
        float animatedValue = (float)updatedAnimation.getAnimatedValue();
        textView.setTranslationX(animatedValue);
    }
});

In the onAnimationUpdate() method you can access the updated animation value and use it in a property of one of your views. For more information on listeners, see the section about Animation listeners.

Animate using ObjectAnimator

The ObjectAnimator is a subclass of the ValueAnimator (discussed in the previous section) and combines the timing engine and value computation of ValueAnimator with the ability to animate a named property of a target object. This makes animating any object much easier, as you no longer need to implement the ValueAnimator.AnimatorUpdateListener, because the animated property updates automatically.

Instantiating an ObjectAnimator is similar to a ValueAnimator, but you also specify the object and the name of that object's property (as a String) along with the values to animate between:

ObjectAnimator.ofFloat(textView, "translationX", 100f).apply {
    duration = 1000
    start()
}

ObjectAnimator animation = ObjectAnimator.ofFloat(textView, "translationX", 100f);
animation.setDuration(1000);
animation.start();

To have the ObjectAnimator update properties correctly, you must do the following:

• The object property that you are animating must have a setter function (in camel case) in the form of set<PropertyName>(). Because the ObjectAnimator automatically updates the property during animation, it must be able to access the property with this setter method. For example, if the property name is foo, you need to have a setFoo() method. If this setter method does not exist, you have three options:
  • Add the setter method to the class if you have the rights to do so.
  • Use a wrapper class that you have rights to change and have that wrapper receive the value with a valid setter method and forward it to the original object.
  • Use ValueAnimator instead.
• If you specify only one value for the values... parameter in one of the ObjectAnimator factory methods, it is assumed to be the ending value of the animation. Therefore, the object property that you are animating must have a getter function that is used to obtain the starting value of the animation. The getter function must be in the form of get<PropertyName>(). For example, if the property name is foo, you need to have a getFoo() method.
• The getter (if needed) and setter methods of the property that you are animating must operate on the same type as the starting and ending values that you specify to ObjectAnimator. For example, you must have targetObject.setPropName(float) and targetObject.getPropName() if you construct the following ObjectAnimator:

  ObjectAnimator.ofFloat(targetObject, "propName", 1f)

• Depending on what property or object you are animating, you might need to call the invalidate() method on a View to force the screen to redraw itself with the updated animated values. You do this in the onAnimationUpdate() callback. For example, animating the color property of a Drawable object only causes updates to the screen when that object redraws itself. All of the property setters on View, such as setAlpha() and setTranslationX() invalidate the View properly, so you do not need to invalidate the View when calling these methods with new values. For more information on listeners, see the section about Animation listeners.

Choreograph multiple animations using an AnimatorSet

In many cases, you want to play an animation that depends on when another animation starts or finishes. The Android system lets you bundle animations together into an AnimatorSet, so that you can specify whether to start animations simultaneously, sequentially, or after a specified delay. You can also nest AnimatorSet objects within each other.

The following code snippet plays the following Animator objects in the following manner:

1. Plays bounceAnim.
2. Plays squashAnim1, squashAnim2, stretchAnim1, and stretchAnim2 at the same time.
3. Plays bounceBackAnim.
4. Plays fadeAnim.

val bouncer = AnimatorSet().apply {
    play(bounceAnim).before(squashAnim1)
    play(squashAnim1).with(squashAnim2)
    play(squashAnim1).with(stretchAnim1)
    play(squashAnim1).with(stretchAnim2)
    play(bounceBackAnim).after(stretchAnim2)
}
val fadeAnim = ObjectAnimator.ofFloat(newBall, "alpha", 1f, 0f).apply {
    duration = 250
}
AnimatorSet().apply {
    play(bouncer).before(fadeAnim)
    start()
}

AnimatorSet bouncer = new AnimatorSet();
bouncer.play(bounceAnim).before(squashAnim1);
bouncer.play(squashAnim1).with(squashAnim2);
bouncer.play(squashAnim1).with(stretchAnim1);
bouncer.play(squashAnim1).with(stretchAnim2);
bouncer.play(bounceBackAnim).after(stretchAnim2);
ValueAnimator fadeAnim = ObjectAnimator.ofFloat(newBall, "alpha", 1f, 0f);
fadeAnim.setDuration(250);
AnimatorSet animatorSet = new AnimatorSet();
animatorSet.play(bouncer).before(fadeAnim);
animatorSet.start();

Animation listeners

You can listen for important events during an animation's duration with the listeners described below.

• Animator.AnimatorListener
  • onAnimationStart() - Called when the animation starts.
  • onAnimationEnd() - Called when the animation ends.
  • onAnimationRepeat() - Called when the animation repeats itself.
  • onAnimationCancel() - Called when the animation is canceled. A cancelled animation also calls onAnimationEnd(), regardless of how they were ended.
• ValueAnimator.AnimatorUpdateListener

  • onAnimationUpdate() - called on every frame of the animation. Listen to this event to use the calculated values generated by ValueAnimator during an animation. To use the value, query the ValueAnimator object passed into the event to get the current animated value with the getAnimatedValue() method. Implementing this listener is required if you use ValueAnimator.

    Depending on what property or object you are animating, you might need to call invalidate() on a View to force that area of the screen to redraw itself with the new animated values. For example, animating the color property of a Drawable object only cause updates to the screen when that object redraws itself. All of the property setters on View, such as setAlpha() and setTranslationX() invalidate the View properly, so you do not need to invalidate the View when calling these methods with new values.

You can extend the AnimatorListenerAdapter class instead of implementing the Animator.AnimatorListener interface, if you do not want to implement all of the methods of the Animator.AnimatorListener interface. The AnimatorListenerAdapter class provides empty implementations of the methods that you can choose to override.

For example, the following code snippet creates an AnimatorListenerAdapter for just the onAnimationEnd() callback:

ObjectAnimator.ofFloat(newBall, "alpha", 1f, 0f).apply {
    duration = 250
    addListener(object : AnimatorListenerAdapter() {
        override fun onAnimationEnd(animation: Animator) {
            balls.remove((animation as ObjectAnimator).target)
        }
    })
}

ValueAnimator fadeAnim = ObjectAnimator.ofFloat(newBall, "alpha", 1f, 0f);
fadeAnim.setDuration(250);
fadeAnim.addListener(new AnimatorListenerAdapter() {
public void onAnimationEnd(Animator animation) {
    balls.remove(((ObjectAnimator)animation).getTarget());
}

Animate layout changes to ViewGroup objects

The property animation system provides the capability to animate changes to ViewGroup objects as well as provide an easy way to animate View objects themselves.

You can animate layout changes within a ViewGroup with the LayoutTransition class. Views inside a ViewGroup can go through an appearing and disappearing animation when you add them to or remove them from a ViewGroup or when you call a View's setVisibility() method with VISIBLE, INVISIBLE, or GONE. The remaining Views in the ViewGroup can also animate into their new positions when you add or remove Views. You can define the following animations in a LayoutTransition object by calling setAnimator() and passing in an Animator object with one of the following LayoutTransition constants:

• APPEARING - A flag indicating the animation that runs on items that are appearing in the container.
• CHANGE_APPEARING - A flag indicating the animation that runs on items that are changing due to a new item appearing in the container.
• DISAPPEARING - A flag indicating the animation that runs on items that are disappearing from the container.
• CHANGE_DISAPPEARING - A flag indicating the animation that runs on items that are changing due to an item disappearing from the container.

You can define your own custom animations for these four types of events to customize the look of your layout transitions or just tell the animation system to use the default animations.

To set the android:animateLayoutchanges attribute to true for the ViewGroup do the following:

<LinearLayout
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:id="@+id/verticalContainer"
    android:animateLayoutChanges="true" />

Setting this attribute to true automatically animates Views that are added or removed from the ViewGroup as well as the remaining Views in the ViewGroup.

Animate view state changes using StateListAnimator

The StateListAnimator class lets you define animators that run when the state of a view changes. This object behaves as a wrapper for an Animator object, calling that animation whenever the specified view state (such as "pressed" or "focused") changes.

The StateListAnimator can be defined in an XML resource with a root <selector> element and child <item> elements that each specify a different view state defined by the StateListAnimator class. Each <item> contains the definition for a property animation set.

For example, the following file creates a state list animator that changes the x and y scale of the view when it's pressed:

res/xml/animate_scale.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- the pressed state; increase x and y size to 150% -->
    <item android:state_pressed="true">
        <set>
            <objectAnimator android:propertyName="scaleX"
                android:duration="@android:integer/config_shortAnimTime"
                android:valueTo="1.5"
                android:valueType="floatType"/>
            <objectAnimator android:propertyName="scaleY"
                android:duration="@android:integer/config_shortAnimTime"
                android:valueTo="1.5"
                android:valueType="floatType"/>
        </set>
    </item>
    <!-- the default, non-pressed state; set x and y size to 100% -->
    <item android:state_pressed="false">
        <set>
            <objectAnimator android:propertyName="scaleX"
                android:duration="@android:integer/config_shortAnimTime"
                android:valueTo="1"
                android:valueType="floatType"/>
            <objectAnimator android:propertyName="scaleY"
                android:duration="@android:integer/config_shortAnimTime"
                android:valueTo="1"
                android:valueType="floatType"/>
        </set>
    </item>
</selector>

To attach the state list animator to a view, add the android:stateListAnimator attribute as follows:

<Button android:stateListAnimator="@xml/animate_scale"
        ... />

Now the animations defined in animate_scale.xml are used when this button's state changes.

Or to instead assign a state list animator to a view in your code, use the AnimatorInflater.loadStateListAnimator() method, and assign the animator to your view with the View.setStateListAnimator() method.

Or instead of animating properties of the view, you can play a drawable animation between state changes, using AnimatedStateListDrawable. Some of the system widgets in Android 5.0 use these animations by default. The following example shows how to define an AnimatedStateListDrawable as an XML resource:

<!-- res/drawable/myanimstatedrawable.xml -->
<animated-selector
    xmlns:android="http://schemas.android.com/apk/res/android">

    <!-- provide a different drawable for each state-->
    <item android:id="@+id/pressed" android:drawable="@drawable/drawableP"
        android:state_pressed="true"/>
    <item android:id="@+id/focused" android:drawable="@drawable/drawableF"
        android:state_focused="true"/>
    <item android:id="@id/default"
        android:drawable="@drawable/drawableD"/>

    <!-- specify a transition -->
    <transition android:fromId="@+id/default" android:toId="@+id/pressed">
        <animation-list>
            <item android:duration="15" android:drawable="@drawable/dt1"/>
            <item android:duration="15" android:drawable="@drawable/dt2"/>
            ...
        </animation-list>
    </transition>
    ...
</animated-selector>

Use a TypeEvaluator

If you want to animate a type that is unknown to the Android system, you can create your own evaluator by implementing the TypeEvaluator interface. The types that are known by the Android system are int, float, or a color, which are supported by the IntEvaluator, FloatEvaluator, and ArgbEvaluator type evaluators.

There is only one method to implement in the TypeEvaluator interface, the evaluate() method. This allows the animator that you are using to return an appropriate value for your animated property at the current point of the animation. The FloatEvaluator class demonstrates how to do this:

private class FloatEvaluator : TypeEvaluator<Any> {

    override fun evaluate(fraction: Float, startValue: Any, endValue: Any): Any {
        return (startValue as Number).toFloat().let { startFloat ->
            startFloat + fraction * ((endValue as Number).toFloat() - startFloat)
        }
    }

}

public class FloatEvaluator implements TypeEvaluator {

    public Object evaluate(float fraction, Object startValue, Object endValue) {
        float startFloat = ((Number) startValue).floatValue();
        return startFloat + fraction * (((Number) endValue).floatValue() - startFloat);
    }
}

Note: When ValueAnimator (or ObjectAnimator) runs, it calculates a current elapsed fraction of the animation (a value between 0 and 1) and then calculates an interpolated version of that depending on what interpolator that you are using. The interpolated fraction is what your TypeEvaluator receives through the fraction parameter, so you do not have to take into account the interpolator when calculating animated values.

Use Interpolators

An interpolator define how specific values in an animation are calculated as a function of time. For example, you can specify animations to happen linearly across the whole animation, meaning the animation moves evenly the entire time, or you can specify animations to use non-linear time, for example, using acceleration or deceleration at the beginning or end of the animation.

Interpolators in the animation system receive a fraction from Animators that represent the elapsed time of the animation. Interpolators modify this fraction to coincide with the type of animation that it aims to provide. The Android system provides a set of common interpolators in the android.view.animation package. If none of these suit your needs, you can implement the TimeInterpolator interface and create your own.

As an example, how the default interpolator AccelerateDecelerateInterpolator and the LinearInterpolator calculate interpolated fractions are compared below. The LinearInterpolator has no effect on the elapsed fraction. The AccelerateDecelerateInterpolator accelerates into the animation and decelerates out of it. The following methods define the logic for these interpolators:

AccelerateDecelerateInterpolator

override fun getInterpolation(input: Float): Float =
        (Math.cos((input + 1) * Math.PI) / 2.0f).toFloat() + 0.5f

@Override
public float getInterpolation(float input) {
    return (float)(Math.cos((input + 1) * Math.PI) / 2.0f) + 0.5f;
}

LinearInterpolator

override fun getInterpolation(input: Float): Float = input

@Override
public float getInterpolation(float input) {
    return input;
}

The following table represents the approximate values that are calculated by these interpolators for an animation that lasts 1000ms:

As the table shows, the LinearInterpolator changes the values at the same speed, .2 for every 200ms that passes. The AccelerateDecelerateInterpolator changes the values faster than LinearInterpolator between 200ms and 600ms and slower between 600ms and 1000ms.

Specify keyframes

A Keyframe object consists of a time/value pair that lets you define a specific state at a specific time of an animation. Each keyframe can also have its own interpolator to control the behavior of the animation in the interval between the previous keyframe's time and the time of this keyframe.

To instantiate a Keyframe object, you must use one of the factory methods, ofInt(), ofFloat(), or ofObject() to obtain the appropriate type of Keyframe. You then call the ofKeyframe() factory method to obtain a PropertyValuesHolder object. Once you have the object, you can obtain an animator by passing in the PropertyValuesHolder object and the object to animate. The following code snippet demonstrates how to do this:

val kf0 = Keyframe.ofFloat(0f, 0f)
val kf1 = Keyframe.ofFloat(.5f, 360f)
val kf2 = Keyframe.ofFloat(1f, 0f)
val pvhRotation = PropertyValuesHolder.ofKeyframe("rotation", kf0, kf1, kf2)
ObjectAnimator.ofPropertyValuesHolder(target, pvhRotation).apply {
    duration = 5000
}

Keyframe kf0 = Keyframe.ofFloat(0f, 0f);
Keyframe kf1 = Keyframe.ofFloat(.5f, 360f);
Keyframe kf2 = Keyframe.ofFloat(1f, 0f);
PropertyValuesHolder pvhRotation = PropertyValuesHolder.ofKeyframe("rotation", kf0, kf1, kf2);
ObjectAnimator rotationAnim = ObjectAnimator.ofPropertyValuesHolder(target, pvhRotation);
rotationAnim.setDuration(5000);

Animate views

The property animation system allow streamlined animation of View objects and offers a few advantages over the view animation system. The view animation system transformed View objects by changing the way that they were drawn. This was handled in the container of each View, because the View itself had no properties to manipulate. This resulted in the View being animated, but caused no change in the View object itself. This led to behavior such as an object still existing in its original location, even though it was drawn on a different location on the screen. In Android 3.0, new properties and the corresponding getter and setter methods were added to eliminate this drawback.

The property animation system can animate Views on the screen by changing the actual properties in the View objects. In addition, Views also automatically call the invalidate() method to refresh the screen whenever its properties are changed. The new properties in the View class that facilitate property animations are:

• translationX and translationY: These properties control where the View is located as a delta from its left and top coordinates which are set by its layout container.
• rotation, rotationX, and rotationY: These properties control the rotation in 2D (rotation property) and 3D around the pivot point.
• scaleX and scaleY: These properties control the 2D scaling of a View around its pivot point.
• pivotX and pivotY: These properties control the location of the pivot point, around which the rotation and scaling transforms occur. By default, the pivot point is located at the center of the object.
• x and y: These are simple utility properties to describe the final location of the View in its container, as a sum of the left and top values and translationX and translationY values.
• alpha: Represents the alpha transparency on the View. This value is 1 (opaque) by default, with a value of 0 representing full transparency (not visible).

To animate a property of a View object, such as its color or rotation value, all you need to do is create a property animator and specify the View property that you want to animate. For example:

ObjectAnimator.ofFloat(myView, "rotation", 0f, 360f)

ObjectAnimator.ofFloat(myView, "rotation", 0f, 360f);

For more information on creating animators, see the sections on animating with ValueAnimator and ObjectAnimator.

Animate using ViewPropertyAnimator

The ViewPropertyAnimator provides a simple way to animate several properties of a View in parallel, using a single underlying Animator object. It behaves much like an ObjectAnimator, because it modifies the actual values of the view's properties, but is more efficient when animating many properties at once. In addition, the code for using the ViewPropertyAnimator is much more concise and easier to read. The following code snippets show the differences in using multiple ObjectAnimator objects, a single ObjectAnimator, and the ViewPropertyAnimator when simultaneously animating the x and y property of a view.

Multiple ObjectAnimator objects

val animX = ObjectAnimator.ofFloat(myView, "x", 50f)
val animY = ObjectAnimator.ofFloat(myView, "y", 100f)
AnimatorSet().apply {
    playTogether(animX, animY)
    start()
}

ObjectAnimator animX = ObjectAnimator.ofFloat(myView, "x", 50f);
ObjectAnimator animY = ObjectAnimator.ofFloat(myView, "y", 100f);
AnimatorSet animSetXY = new AnimatorSet();
animSetXY.playTogether(animX, animY);
animSetXY.start();

One ObjectAnimator

val pvhX = PropertyValuesHolder.ofFloat("x", 50f)
val pvhY = PropertyValuesHolder.ofFloat("y", 100f)
ObjectAnimator.ofPropertyValuesHolder(myView, pvhX, pvhY).start()

PropertyValuesHolder pvhX = PropertyValuesHolder.ofFloat("x", 50f);
PropertyValuesHolder pvhY = PropertyValuesHolder.ofFloat("y", 100f);
ObjectAnimator.ofPropertyValuesHolder(myView, pvhX, pvhY).start();

ViewPropertyAnimator

myView.animate().x(50f).y(100f)

myView.animate().x(50f).y(100f);

For more detailed information about ViewPropertyAnimator, see the corresponding Android Developers blog post.

Declare animations in XML

The property animation system lets you declare property animations with XML instead of doing it programmatically. By defining your animations in XML, you can easily reuse your animations in multiple activities and more easily edit the animation sequence.

To distinguish animation files that use the new property animation APIs from those that use the legacy view animation framework, starting with Android 3.1, you should save the XML files for property animations in the res/animator/ directory.

The following property animation classes have XML declaration support with the following XML tags:

• ValueAnimator - <animator>
• ObjectAnimator - <objectAnimator>
• AnimatorSet - <set>

To find the attributes that you can use in your XML declaration, see Animation resources. The following example plays the two sets of object animations sequentially, with the first nested set playing two object animations together:

<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:

(AnimatorInflater.loadAnimator(myContext, R.animator.property_animator) as AnimatorSet).apply {
    setTarget(myObject)
    start()
}

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

You can also declare a ValueAnimator in XML, as shown in the following example:

<animator xmlns:android="http://schemas.android.com/apk/res/android"
    android:duration="1000"
    android:valueType="floatType"
    android:valueFrom="0f"
    android:valueTo="-100f" />

To use the previous ValueAnimator in your code, you must inflate the object, add an AnimatorUpdateListener, get the updated animation value, and use it in a property of one of your views, as shown in the following code:

(AnimatorInflater.loadAnimator(this, R.animator.animator) as ValueAnimator).apply {
    addUpdateListener { updatedAnimation ->
        textView.translationX = updatedAnimation.animatedValue as Float
    }

    start()
}

ValueAnimator xmlAnimator = (ValueAnimator) AnimatorInflater.loadAnimator(this,
        R.animator.animator);
xmlAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
    @Override
    public void onAnimationUpdate(ValueAnimator updatedAnimation) {
        float animatedValue = (float)updatedAnimation.getAnimatedValue();
        textView.setTranslationX(animatedValue);
    }
});

xmlAnimator.start();

For information about the XML syntax for defining property animations, see Animation resources .

Potential effects on UI performance

Animators that update the UI cause extra rendering work for every frame in which the animation runs. For this reason, using resource intensive animations can negatively impact the performance of your app.

Work required to animate your UI is added to the animation stage of the rendering pipeline. You can find out if your animations impact the performance of your app by enabling Profile GPU Rendering and monitoring the animation stage. For more information, see Profile GPU rendering walkthrough.