/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.animation;

import android.annotation.CallSuper;
import android.annotation.IntDef;
import android.annotation.TestApi;
import android.os.Looper;
import android.os.Trace;
import android.util.AndroidRuntimeException;
import android.util.Log;
import android.view.animation.AccelerateDecelerateInterpolator;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.view.animation.LinearInterpolator;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.ArrayList;
import java.util.HashMap;

This class provides a simple timing engine for running animations
which calculate animated values and set them on target objects.
There is a single timing pulse that all animations use. It runs in a
custom handler to ensure that property changes happen on the UI thread.
By default, ValueAnimator uses non-linear time interpolation, via the AccelerateDecelerateInterpolator class, which accelerates into and decelerates out of an animation. This behavior can be changed by calling setInterpolator(TimeInterpolator).
Animators can be created from either code or resource files. Here is an example
of a ValueAnimator resource file:
{@sample development/samples/ApiDemos/res/anim/animator.xml ValueAnimatorResources}
Starting from API 23, it is also possible to use a combination of PropertyValuesHolder and Keyframe resource tags to create a multi-step animation. Note that you can specify explicit fractional values (from 0 to 1) for each keyframe to determine when, in the overall duration, the animation should arrive at that value. Alternatively, you can leave the fractions off and the keyframes will be equally distributed within the total duration:
{@sample development/samples/ApiDemos/res/anim/value_animator_pvh_kf.xml
ValueAnimatorKeyframeResources}

Developer Guides
For more information about animating with ValueAnimator, read the Property
Animation developer guide.

/**
 * This class provides a simple timing engine for running animations
 * which calculate animated values and set them on target objects.
 *
 * <p>There is a single timing pulse that all animations use. It runs in a
 * custom handler to ensure that property changes happen on the UI thread.</p>
 *
 * <p>By default, ValueAnimator uses non-linear time interpolation, via the
 * {@link AccelerateDecelerateInterpolator} class, which accelerates into and decelerates
 * out of an animation. This behavior can be changed by calling
 * {@link ValueAnimator#setInterpolator(TimeInterpolator)}.</p>
 *
 * <p>Animators can be created from either code or resource files. Here is an example
 * of a ValueAnimator resource file:</p>
 *
 * {@sample development/samples/ApiDemos/res/anim/animator.xml ValueAnimatorResources}
 *
 * <p>Starting from API 23, it is also possible to use a combination of {@link PropertyValuesHolder}
 * and {@link Keyframe} resource tags to create a multi-step animation.
 * Note that you can specify explicit fractional values (from 0 to 1) for
 * each keyframe to determine when, in the overall duration, the animation should arrive at that
 * value. Alternatively, you can leave the fractions off and the keyframes will be equally
 * distributed within the total duration:</p>
 *
 * {@sample development/samples/ApiDemos/res/anim/value_animator_pvh_kf.xml
 * ValueAnimatorKeyframeResources}
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 * <p>For more information about animating with {@code ValueAnimator}, read the
 * <a href="{@docRoot}guide/topics/graphics/prop-animation.html#value-animator">Property
 * Animation</a> developer guide.</p>
 * </div>
 */
@SuppressWarnings("unchecked")
public class ValueAnimator extends Animator implements AnimationHandler.AnimationFrameCallback {
    private static final String TAG = "ValueAnimator";
    private static final boolean DEBUG = false;

    
Internal constants
/**
     * Internal constants
     */
    private static float sDurationScale = 1.0f;

    /**
     * Internal variables
     * NOTE: This object implements the clone() method, making a deep copy of any referenced
     * objects. As other non-trivial fields are added to this class, make sure to add logic
     * to clone() to make deep copies of them.
     */

    
The first time that the animation's animateFrame() method is called. This time is used to
determine elapsed time (and therefore the elapsed fraction) in subsequent calls
to animateFrame().
Whenever mStartTime is set, you must also update mStartTimeCommitted.
/**
     * The first time that the animation's animateFrame() method is called. This time is used to
     * determine elapsed time (and therefore the elapsed fraction) in subsequent calls
     * to animateFrame().
     *
     * Whenever mStartTime is set, you must also update mStartTimeCommitted.
     */
    long mStartTime = -1;

    
When true, the start time has been firmly committed as a chosen reference point in
time by which the progress of the animation will be evaluated.  When false, the
start time may be updated when the first animation frame is committed so as
to compensate for jank that may have occurred between when the start time was
initialized and when the frame was actually drawn.
This flag is generally set to false during the first frame of the animation
when the animation playing state transitions from STOPPED to RUNNING or
resumes after having been paused.  This flag is set to true when the start time
is firmly committed and should not be further compensated for jank.
/**
     * When true, the start time has been firmly committed as a chosen reference point in
     * time by which the progress of the animation will be evaluated.  When false, the
     * start time may be updated when the first animation frame is committed so as
     * to compensate for jank that may have occurred between when the start time was
     * initialized and when the frame was actually drawn.
     *
     * This flag is generally set to false during the first frame of the animation
     * when the animation playing state transitions from STOPPED to RUNNING or
     * resumes after having been paused.  This flag is set to true when the start time
     * is firmly committed and should not be further compensated for jank.
     */
    boolean mStartTimeCommitted;

    
Set when setCurrentPlayTime() is called. If negative, animation is not currently seeked
to a value.
/**
     * Set when setCurrentPlayTime() is called. If negative, animation is not currently seeked
     * to a value.
     */
    float mSeekFraction = -1;

    
Set on the next frame after pause() is called, used to calculate a new startTime
or delayStartTime which allows the animator to continue from the point at which
it was paused. If negative, has not yet been set.
/**
     * Set on the next frame after pause() is called, used to calculate a new startTime
     * or delayStartTime which allows the animator to continue from the point at which
     * it was paused. If negative, has not yet been set.
     */
    private long mPauseTime;

    
Set when an animator is resumed. This triggers logic in the next frame which
actually resumes the animator.
/**
     * Set when an animator is resumed. This triggers logic in the next frame which
     * actually resumes the animator.
     */
    private boolean mResumed = false;

    // The time interpolator to be used if none is set on the animation
    private static final TimeInterpolator sDefaultInterpolator =
            new AccelerateDecelerateInterpolator();

    
Flag to indicate whether this animator is playing in reverse mode, specifically
by being started or interrupted by a call to reverse(). This flag is different than
mPlayingBackwards, which indicates merely whether the current iteration of the
animator is playing in reverse. It is used in corner cases to determine proper end
behavior.
/**
     * Flag to indicate whether this animator is playing in reverse mode, specifically
     * by being started or interrupted by a call to reverse(). This flag is different than
     * mPlayingBackwards, which indicates merely whether the current iteration of the
     * animator is playing in reverse. It is used in corner cases to determine proper end
     * behavior.
     */
    private boolean mReversing;

    
Tracks the overall fraction of the animation, ranging from 0 to mRepeatCount + 1
/**
     * Tracks the overall fraction of the animation, ranging from 0 to mRepeatCount + 1
     */
    private float mOverallFraction = 0f;

    
Tracks current elapsed/eased fraction, for querying in getAnimatedFraction().
This is calculated by interpolating the fraction (range: [0, 1]) in the current iteration.
/**
     * Tracks current elapsed/eased fraction, for querying in getAnimatedFraction().
     * This is calculated by interpolating the fraction (range: [0, 1]) in the current iteration.
     */
    private float mCurrentFraction = 0f;

    
Tracks the time (in milliseconds) when the last frame arrived.
/**
     * Tracks the time (in milliseconds) when the last frame arrived.
     */
    private long mLastFrameTime = -1;

    
Tracks the time (in milliseconds) when the first frame arrived. Note the frame may arrive
during the start delay.
/**
     * Tracks the time (in milliseconds) when the first frame arrived. Note the frame may arrive
     * during the start delay.
     */
    private long mFirstFrameTime = -1;

    
Additional playing state to indicate whether an animator has been start()'d. There is
some lag between a call to start() and the first animation frame. We should still note
that the animation has been started, even if it's first animation frame has not yet
happened, and reflect that state in isRunning().
Note that delayed animations are different: they are not started until their first
animation frame, which occurs after their delay elapses.
/**
     * Additional playing state to indicate whether an animator has been start()'d. There is
     * some lag between a call to start() and the first animation frame. We should still note
     * that the animation has been started, even if it's first animation frame has not yet
     * happened, and reflect that state in isRunning().
     * Note that delayed animations are different: they are not started until their first
     * animation frame, which occurs after their delay elapses.
     */
    private boolean mRunning = false;

    
Additional playing state to indicate whether an animator has been start()'d, whether or
not there is a nonzero startDelay.
/**
     * Additional playing state to indicate whether an animator has been start()'d, whether or
     * not there is a nonzero startDelay.
     */
    private boolean mStarted = false;

    
Tracks whether we've notified listeners of the onAnimationStart() event. This can be
complex to keep track of since we notify listeners at different times depending on
startDelay and whether start() was called before end().
/**
     * Tracks whether we've notified listeners of the onAnimationStart() event. This can be
     * complex to keep track of since we notify listeners at different times depending on
     * startDelay and whether start() was called before end().
     */
    private boolean mStartListenersCalled = false;

    
Flag that denotes whether the animation is set up and ready to go. Used to
set up animation that has not yet been started.
/**
     * Flag that denotes whether the animation is set up and ready to go. Used to
     * set up animation that has not yet been started.
     */
    boolean mInitialized = false;

    
Flag that tracks whether animation has been requested to end.
/**
     * Flag that tracks whether animation has been requested to end.
     */
    private boolean mAnimationEndRequested = false;

    //
    // Backing variables
    //

    // How long the animation should last in ms
    private long mDuration = 300;

    // The amount of time in ms to delay starting the animation after start() is called. Note
    // that this start delay is unscaled. When there is a duration scale set on the animator, the
    // scaling factor will be applied to this delay.
    private long mStartDelay = 0;

    // The number of times the animation will repeat. The default is 0, which means the animation
    // will play only once
    private int mRepeatCount = 0;

    
The type of repetition that will occur when repeatMode is nonzero. RESTART means the
animation will start from the beginning on every new cycle. REVERSE means the animation
will reverse directions on each iteration.
/**
     * The type of repetition that will occur when repeatMode is nonzero. RESTART means the
     * animation will start from the beginning on every new cycle. REVERSE means the animation
     * will reverse directions on each iteration.
     */
    private int mRepeatMode = RESTART;

    
Whether or not the animator should register for its own animation callback to receive
animation pulse.
/**
     * Whether or not the animator should register for its own animation callback to receive
     * animation pulse.
     */
    private boolean mSelfPulse = true;

    
Whether or not the animator has been requested to start without pulsing. This flag gets set
in startWithoutPulsing(), and reset in start().
/**
     * Whether or not the animator has been requested to start without pulsing. This flag gets set
     * in startWithoutPulsing(), and reset in start().
     */
    private boolean mSuppressSelfPulseRequested = false;

    
The time interpolator to be used. The elapsed fraction of the animation will be passed
through this interpolator to calculate the interpolated fraction, which is then used to
calculate the animated values.
/**
     * The time interpolator to be used. The elapsed fraction of the animation will be passed
     * through this interpolator to calculate the interpolated fraction, which is then used to
     * calculate the animated values.
     */
    private TimeInterpolator mInterpolator = sDefaultInterpolator;

    
The set of listeners to be sent events through the life of an animation.
/**
     * The set of listeners to be sent events through the life of an animation.
     */
    ArrayList<AnimatorUpdateListener> mUpdateListeners = null;

    
The property/value sets being animated.
/**
     * The property/value sets being animated.
     */
    PropertyValuesHolder[] mValues;

    
A hashmap of the PropertyValuesHolder objects. This map is used to lookup animated values
by property name during calls to getAnimatedValue(String).
/**
     * A hashmap of the PropertyValuesHolder objects. This map is used to lookup animated values
     * by property name during calls to getAnimatedValue(String).
     */
    HashMap<String, PropertyValuesHolder> mValuesMap;

    
If set to non-negative value, this will override sDurationScale. /**
     * If set to non-negative value, this will override {@link #sDurationScale}.
     */
    private float mDurationScale = -1f;

    /**
     * Public constants
     */

    
@hide
/** @hide */
    @IntDef({RESTART, REVERSE})
    @Retention(RetentionPolicy.SOURCE)
    public @interface RepeatMode {}

    
When the animation reaches the end and repeatCount is INFINITE
or a positive value, the animation restarts from the beginning.
/**
     * When the animation reaches the end and <code>repeatCount</code> is INFINITE
     * or a positive value, the animation restarts from the beginning.
     */
    public static final int RESTART = 1;
    
When the animation reaches the end and repeatCount is INFINITE
or a positive value, the animation reverses direction on every iteration.
/**
     * When the animation reaches the end and <code>repeatCount</code> is INFINITE
     * or a positive value, the animation reverses direction on every iteration.
     */
    public static final int REVERSE = 2;
    
This value used used with the setRepeatCount(int) property to repeat the animation indefinitely. /**
     * This value used used with the {@link #setRepeatCount(int)} property to repeat
     * the animation indefinitely.
     */
    public static final int INFINITE = -1;

    
@hide
/**
     * @hide
     */
    @TestApi
    public static void setDurationScale(float durationScale) {
        sDurationScale = durationScale;
    }

    
@hide
/**
     * @hide
     */
    @TestApi
    public static float getDurationScale() {
        return sDurationScale;
    }

    
Returns whether animators are currently enabled, system-wide. By default, all
animators are enabled. This can change if either the user sets a Developer Option
to set the animator duration scale to 0 or by Battery Savery mode being enabled
(which disables all animations).
Developers should not typically need to call this method, but should an app wish
to show a different experience when animators are disabled, this return value
can be used as a decider of which experience to offer.
Returns:
boolean Whether animators are currently enabled. The default value is
true./**
     * Returns whether animators are currently enabled, system-wide. By default, all
     * animators are enabled. This can change if either the user sets a Developer Option
     * to set the animator duration scale to 0 or by Battery Savery mode being enabled
     * (which disables all animations).
     *
     * <p>Developers should not typically need to call this method, but should an app wish
     * to show a different experience when animators are disabled, this return value
     * can be used as a decider of which experience to offer.
     *
     * @return boolean Whether animators are currently enabled. The default value is
     * <code>true</code>.
     */
    public static boolean areAnimatorsEnabled() {
        return !(sDurationScale == 0);
    }

    
Creates a new ValueAnimator object. This default constructor is primarily for
use internally; the factory methods which take parameters are more generally
useful.
/**
     * Creates a new ValueAnimator object. This default constructor is primarily for
     * use internally; the factory methods which take parameters are more generally
     * useful.
     */
    public ValueAnimator() {
    }

    
Constructs and returns a ValueAnimator that animates between int values. A single
value implies that that value is the one being animated to. However, this is not typically
useful in a ValueAnimator object because there is no way for the object to determine the
starting value for the animation (unlike ObjectAnimator, which can derive that value
from the target object and property being animated). Therefore, there should typically
be two or more values.
Params:
values – A set of values that the animation will animate between over time.
Returns:
A ValueAnimator object that is set up to animate between the given values./**
     * Constructs and returns a ValueAnimator that animates between int values. A single
     * value implies that that value is the one being animated to. However, this is not typically
     * useful in a ValueAnimator object because there is no way for the object to determine the
     * starting value for the animation (unlike ObjectAnimator, which can derive that value
     * from the target object and property being animated). Therefore, there should typically
     * be two or more values.
     *
     * @param values A set of values that the animation will animate between over time.
     * @return A ValueAnimator object that is set up to animate between the given values.
     */
    public static ValueAnimator ofInt(int... values) {
        ValueAnimator anim = new ValueAnimator();
        anim.setIntValues(values);
        return anim;
    }

    
Constructs and returns a ValueAnimator that animates between color values. A single
value implies that that value is the one being animated to. However, this is not typically
useful in a ValueAnimator object because there is no way for the object to determine the
starting value for the animation (unlike ObjectAnimator, which can derive that value
from the target object and property being animated). Therefore, there should typically
be two or more values.
Params:
values – A set of values that the animation will animate between over time.
Returns:
A ValueAnimator object that is set up to animate between the given values./**
     * Constructs and returns a ValueAnimator that animates between color values. A single
     * value implies that that value is the one being animated to. However, this is not typically
     * useful in a ValueAnimator object because there is no way for the object to determine the
     * starting value for the animation (unlike ObjectAnimator, which can derive that value
     * from the target object and property being animated). Therefore, there should typically
     * be two or more values.
     *
     * @param values A set of values that the animation will animate between over time.
     * @return A ValueAnimator object that is set up to animate between the given values.
     */
    public static ValueAnimator ofArgb(int... values) {
        ValueAnimator anim = new ValueAnimator();
        anim.setIntValues(values);
        anim.setEvaluator(ArgbEvaluator.getInstance());
        return anim;
    }

    
Constructs and returns a ValueAnimator that animates between float values. A single
value implies that that value is the one being animated to. However, this is not typically
useful in a ValueAnimator object because there is no way for the object to determine the
starting value for the animation (unlike ObjectAnimator, which can derive that value
from the target object and property being animated). Therefore, there should typically
be two or more values.
Params:
values – A set of values that the animation will animate between over time.
Returns:
A ValueAnimator object that is set up to animate between the given values./**
     * Constructs and returns a ValueAnimator that animates between float values. A single
     * value implies that that value is the one being animated to. However, this is not typically
     * useful in a ValueAnimator object because there is no way for the object to determine the
     * starting value for the animation (unlike ObjectAnimator, which can derive that value
     * from the target object and property being animated). Therefore, there should typically
     * be two or more values.
     *
     * @param values A set of values that the animation will animate between over time.
     * @return A ValueAnimator object that is set up to animate between the given values.
     */
    public static ValueAnimator ofFloat(float... values) {
        ValueAnimator anim = new ValueAnimator();
        anim.setFloatValues(values);
        return anim;
    }

    
Constructs and returns a ValueAnimator that animates between the values
specified in the PropertyValuesHolder objects.
Params:
values – A set of PropertyValuesHolder objects whose values will be animated
between over time.
Returns:
A ValueAnimator object that is set up to animate between the given values./**
     * Constructs and returns a ValueAnimator that animates between the values
     * specified in the PropertyValuesHolder objects.
     *
     * @param values A set of PropertyValuesHolder objects whose values will be animated
     * between over time.
     * @return A ValueAnimator object that is set up to animate between the given values.
     */
    public static ValueAnimator ofPropertyValuesHolder(PropertyValuesHolder... values) {
        ValueAnimator anim = new ValueAnimator();
        anim.setValues(values);
        return anim;
    }
    
Constructs and returns a ValueAnimator that animates between Object values. A single
value implies that that value is the one being animated to. However, this is not typically
useful in a ValueAnimator object because there is no way for the object to determine the
starting value for the animation (unlike ObjectAnimator, which can derive that value
from the target object and property being animated). Therefore, there should typically
be two or more values.
Note: The Object values are stored as references to the original
objects, which means that changes to those objects after this method is called will
affect the values on the animator. If the objects will be mutated externally after
this method is called, callers should pass a copy of those objects instead.
Since ValueAnimator does not know how to animate between arbitrary Objects, this
factory method also takes a TypeEvaluator object that the ValueAnimator will use
to perform that interpolation.
Params:
evaluator – A TypeEvaluator that will be called on each animation frame to
provide the ncessry interpolation between the Object values to derive the animated
value.
values – A set of values that the animation will animate between over time.
Returns:
A ValueAnimator object that is set up to animate between the given values./**
     * Constructs and returns a ValueAnimator that animates between Object values. A single
     * value implies that that value is the one being animated to. However, this is not typically
     * useful in a ValueAnimator object because there is no way for the object to determine the
     * starting value for the animation (unlike ObjectAnimator, which can derive that value
     * from the target object and property being animated). Therefore, there should typically
     * be two or more values.
     *
     * <p><strong>Note:</strong> The Object values are stored as references to the original
     * objects, which means that changes to those objects after this method is called will
     * affect the values on the animator. If the objects will be mutated externally after
     * this method is called, callers should pass a copy of those objects instead.
     *
     * <p>Since ValueAnimator does not know how to animate between arbitrary Objects, this
     * factory method also takes a TypeEvaluator object that the ValueAnimator will use
     * to perform that interpolation.
     *
     * @param evaluator A TypeEvaluator that will be called on each animation frame to
     * provide the ncessry interpolation between the Object values to derive the animated
     * value.
     * @param values A set of values that the animation will animate between over time.
     * @return A ValueAnimator object that is set up to animate between the given values.
     */
    public static ValueAnimator ofObject(TypeEvaluator evaluator, Object... values) {
        ValueAnimator anim = new ValueAnimator();
        anim.setObjectValues(values);
        anim.setEvaluator(evaluator);
        return anim;
    }

    
Sets int values that will be animated between. A single
value implies that that value is the one being animated to. However, this is not typically
useful in a ValueAnimator object because there is no way for the object to determine the
starting value for the animation (unlike ObjectAnimator, which can derive that value
from the target object and property being animated). Therefore, there should typically
be two or more values.
If there are already multiple sets of values defined for this ValueAnimator via more
than one PropertyValuesHolder object, this method will set the values for the first
of those objects.
Params:
values – A set of values that the animation will animate between over time./**
     * Sets int values that will be animated between. A single
     * value implies that that value is the one being animated to. However, this is not typically
     * useful in a ValueAnimator object because there is no way for the object to determine the
     * starting value for the animation (unlike ObjectAnimator, which can derive that value
     * from the target object and property being animated). Therefore, there should typically
     * be two or more values.
     *
     * <p>If there are already multiple sets of values defined for this ValueAnimator via more
     * than one PropertyValuesHolder object, this method will set the values for the first
     * of those objects.</p>
     *
     * @param values A set of values that the animation will animate between over time.
     */
    public void setIntValues(int... values) {
        if (values == null || values.length == 0) {
            return;
        }
        if (mValues == null || mValues.length == 0) {
            setValues(PropertyValuesHolder.ofInt("", values));
        } else {
            PropertyValuesHolder valuesHolder = mValues[0];
            valuesHolder.setIntValues(values);
        }
        // New property/values/target should cause re-initialization prior to starting
        mInitialized = false;
    }

    
Sets float values that will be animated between. A single
value implies that that value is the one being animated to. However, this is not typically
useful in a ValueAnimator object because there is no way for the object to determine the
starting value for the animation (unlike ObjectAnimator, which can derive that value
from the target object and property being animated). Therefore, there should typically
be two or more values.
If there are already multiple sets of values defined for this ValueAnimator via more
than one PropertyValuesHolder object, this method will set the values for the first
of those objects.
Params:
values – A set of values that the animation will animate between over time./**
     * Sets float values that will be animated between. A single
     * value implies that that value is the one being animated to. However, this is not typically
     * useful in a ValueAnimator object because there is no way for the object to determine the
     * starting value for the animation (unlike ObjectAnimator, which can derive that value
     * from the target object and property being animated). Therefore, there should typically
     * be two or more values.
     *
     * <p>If there are already multiple sets of values defined for this ValueAnimator via more
     * than one PropertyValuesHolder object, this method will set the values for the first
     * of those objects.</p>
     *
     * @param values A set of values that the animation will animate between over time.
     */
    public void setFloatValues(float... values) {
        if (values == null || values.length == 0) {
            return;
        }
        if (mValues == null || mValues.length == 0) {
            setValues(PropertyValuesHolder.ofFloat("", values));
        } else {
            PropertyValuesHolder valuesHolder = mValues[0];
            valuesHolder.setFloatValues(values);
        }
        // New property/values/target should cause re-initialization prior to starting
        mInitialized = false;
    }

    
Sets the values to animate between for this animation. A single
value implies that that value is the one being animated to. However, this is not typically
useful in a ValueAnimator object because there is no way for the object to determine the
starting value for the animation (unlike ObjectAnimator, which can derive that value
from the target object and property being animated). Therefore, there should typically
be two or more values.
Note: The Object values are stored as references to the original
objects, which means that changes to those objects after this method is called will
affect the values on the animator. If the objects will be mutated externally after
this method is called, callers should pass a copy of those objects instead.
If there are already multiple sets of values defined for this ValueAnimator via more
than one PropertyValuesHolder object, this method will set the values for the first
of those objects.
There should be a TypeEvaluator set on the ValueAnimator that knows how to interpolate
between these value objects. ValueAnimator only knows how to interpolate between the
primitive types specified in the other setValues() methods.
Params:
values – The set of values to animate between./**
     * Sets the values to animate between for this animation. A single
     * value implies that that value is the one being animated to. However, this is not typically
     * useful in a ValueAnimator object because there is no way for the object to determine the
     * starting value for the animation (unlike ObjectAnimator, which can derive that value
     * from the target object and property being animated). Therefore, there should typically
     * be two or more values.
     *
     * <p><strong>Note:</strong> The Object values are stored as references to the original
     * objects, which means that changes to those objects after this method is called will
     * affect the values on the animator. If the objects will be mutated externally after
     * this method is called, callers should pass a copy of those objects instead.
     *
     * <p>If there are already multiple sets of values defined for this ValueAnimator via more
     * than one PropertyValuesHolder object, this method will set the values for the first
     * of those objects.</p>
     *
     * <p>There should be a TypeEvaluator set on the ValueAnimator that knows how to interpolate
     * between these value objects. ValueAnimator only knows how to interpolate between the
     * primitive types specified in the other setValues() methods.</p>
     *
     * @param values The set of values to animate between.
     */
    public void setObjectValues(Object... values) {
        if (values == null || values.length == 0) {
            return;
        }
        if (mValues == null || mValues.length == 0) {
            setValues(PropertyValuesHolder.ofObject("", null, values));
        } else {
            PropertyValuesHolder valuesHolder = mValues[0];
            valuesHolder.setObjectValues(values);
        }
        // New property/values/target should cause re-initialization prior to starting
        mInitialized = false;
    }

    
Sets the values, per property, being animated between. This function is called internally
by the constructors of ValueAnimator that take a list of values. But a ValueAnimator can
be constructed without values and this method can be called to set the values manually
instead.
Params:
values – The set of values, per property, being animated between./**
     * Sets the values, per property, being animated between. This function is called internally
     * by the constructors of ValueAnimator that take a list of values. But a ValueAnimator can
     * be constructed without values and this method can be called to set the values manually
     * instead.
     *
     * @param values The set of values, per property, being animated between.
     */
    public void setValues(PropertyValuesHolder... values) {
        int numValues = values.length;
        mValues = values;
        mValuesMap = new HashMap<String, PropertyValuesHolder>(numValues);
        for (int i = 0; i < numValues; ++i) {
            PropertyValuesHolder valuesHolder = values[i];
            mValuesMap.put(valuesHolder.getPropertyName(), valuesHolder);
        }
        // New property/values/target should cause re-initialization prior to starting
        mInitialized = false;
    }

    
Returns the values that this ValueAnimator animates between. These values are stored in
PropertyValuesHolder objects, even if the ValueAnimator was created with a simple list
of value objects instead.
Returns:
PropertyValuesHolder[] An array of PropertyValuesHolder objects which hold the
values, per property, that define the animation./**
     * Returns the values that this ValueAnimator animates between. These values are stored in
     * PropertyValuesHolder objects, even if the ValueAnimator was created with a simple list
     * of value objects instead.
     *
     * @return PropertyValuesHolder[] An array of PropertyValuesHolder objects which hold the
     * values, per property, that define the animation.
     */
    public PropertyValuesHolder[] getValues() {
        return mValues;
    }

    
This function is called immediately before processing the first animation
frame of an animation. If there is a nonzero startDelay, the
function is called after that delay ends.
It takes care of the final initialization steps for the
animation.
 
Overrides of this method should call the superclass method to ensure
 that internal mechanisms for the animation are set up correctly.
/**
     * This function is called immediately before processing the first animation
     * frame of an animation. If there is a nonzero <code>startDelay</code>, the
     * function is called after that delay ends.
     * It takes care of the final initialization steps for the
     * animation.
     *
     *  <p>Overrides of this method should call the superclass method to ensure
     *  that internal mechanisms for the animation are set up correctly.</p>
     */
    @CallSuper
    void initAnimation() {
        if (!mInitialized) {
            int numValues = mValues.length;
            for (int i = 0; i < numValues; ++i) {
                mValues[i].init();
            }
            mInitialized = true;
        }
    }

    
Sets the length of the animation. The default duration is 300 milliseconds.
Params:
duration – The length of the animation, in milliseconds. This value cannot
be negative.
Returns:
ValueAnimator The object called with setDuration(). This return
value makes it easier to compose statements together that construct and then set the
duration, as in ValueAnimator.ofInt(0, 10).setDuration(500).start()./**
     * Sets the length of the animation. The default duration is 300 milliseconds.
     *
     * @param duration The length of the animation, in milliseconds. This value cannot
     * be negative.
     * @return ValueAnimator The object called with setDuration(). This return
     * value makes it easier to compose statements together that construct and then set the
     * duration, as in <code>ValueAnimator.ofInt(0, 10).setDuration(500).start()</code>.
     */
    @Override
    public ValueAnimator setDuration(long duration) {
        if (duration < 0) {
            throw new IllegalArgumentException("Animators cannot have negative duration: " +
                    duration);
        }
        mDuration = duration;
        return this;
    }

    
Overrides the global duration scale by a custom value.
Params:
durationScale – The duration scale to set; or -1f to use the global duration scale.
@hide
/**
     * Overrides the global duration scale by a custom value.
     *
     * @param durationScale The duration scale to set; or {@code -1f} to use the global duration
     *                      scale.
     * @hide
     */
    public void overrideDurationScale(float durationScale) {
        mDurationScale = durationScale;
    }

    private float resolveDurationScale() {
        return mDurationScale >= 0f ? mDurationScale : sDurationScale;
    }

    private long getScaledDuration() {
        return (long)(mDuration * resolveDurationScale());
    }

    
Gets the length of the animation. The default duration is 300 milliseconds.
Returns:
The length of the animation, in milliseconds./**
     * Gets the length of the animation. The default duration is 300 milliseconds.
     *
     * @return The length of the animation, in milliseconds.
     */
    @Override
    public long getDuration() {
        return mDuration;
    }

    @Override
    public long getTotalDuration() {
        if (mRepeatCount == INFINITE) {
            return DURATION_INFINITE;
        } else {
            return mStartDelay + (mDuration * (mRepeatCount + 1));
        }
    }

    
Sets the position of the animation to the specified point in time. This time should
be between 0 and the total duration of the animation, including any repetition. If
the animation has not yet been started, then it will not advance forward after it is
set to this time; it will simply set the time to this value and perform any appropriate
actions based on that time. If the animation is already running, then setCurrentPlayTime()
will set the current playing time to this value and continue playing from that point.
Params:
playTime – The time, in milliseconds, to which the animation is advanced or rewound./**
     * Sets the position of the animation to the specified point in time. This time should
     * be between 0 and the total duration of the animation, including any repetition. If
     * the animation has not yet been started, then it will not advance forward after it is
     * set to this time; it will simply set the time to this value and perform any appropriate
     * actions based on that time. If the animation is already running, then setCurrentPlayTime()
     * will set the current playing time to this value and continue playing from that point.
     *
     * @param playTime The time, in milliseconds, to which the animation is advanced or rewound.
     */
    public void setCurrentPlayTime(long playTime) {
        float fraction = mDuration > 0 ? (float) playTime / mDuration : 1;
        setCurrentFraction(fraction);
    }

    
Sets the position of the animation to the specified fraction. This fraction should be between 0 and the total fraction of the animation, including any repetition. That is, a fraction of 0 will position the animation at the beginning, a value of 1 at the end, and a value of 2 at the end of a reversing animator that repeats once. If the animation has not yet been started, then it will not advance forward after it is set to this fraction; it will simply set the fraction to this value and perform any appropriate actions based on that fraction. If the animation is already running, then setCurrentFraction() will set the current fraction to this value and continue playing from that point. AnimatorListener events are not called due to changing the fraction; those events are only processed while the animation is running. 
Params:
fraction – The fraction to which the animation is advanced or rewound. Values
outside the range of 0 to the maximum fraction for the animator will be clamped to
the correct range./**
     * Sets the position of the animation to the specified fraction. This fraction should
     * be between 0 and the total fraction of the animation, including any repetition. That is,
     * a fraction of 0 will position the animation at the beginning, a value of 1 at the end,
     * and a value of 2 at the end of a reversing animator that repeats once. If
     * the animation has not yet been started, then it will not advance forward after it is
     * set to this fraction; it will simply set the fraction to this value and perform any
     * appropriate actions based on that fraction. If the animation is already running, then
     * setCurrentFraction() will set the current fraction to this value and continue
     * playing from that point. {@link Animator.AnimatorListener} events are not called
     * due to changing the fraction; those events are only processed while the animation
     * is running.
     *
     * @param fraction The fraction to which the animation is advanced or rewound. Values
     * outside the range of 0 to the maximum fraction for the animator will be clamped to
     * the correct range.
     */
    public void setCurrentFraction(float fraction) {
        initAnimation();
        fraction = clampFraction(fraction);
        mStartTimeCommitted = true; // do not allow start time to be compensated for jank
        if (isPulsingInternal()) {
            long seekTime = (long) (getScaledDuration() * fraction);
            long currentTime = AnimationUtils.currentAnimationTimeMillis();
            // Only modify the start time when the animation is running. Seek fraction will ensure
            // non-running animations skip to the correct start time.
            mStartTime = currentTime - seekTime;
        } else {
            // If the animation loop hasn't started, or during start delay, the startTime will be
            // adjusted once the delay has passed based on seek fraction.
            mSeekFraction = fraction;
        }
        mOverallFraction = fraction;
        final float currentIterationFraction = getCurrentIterationFraction(fraction, mReversing);
        animateValue(currentIterationFraction);
    }

    
Calculates current iteration based on the overall fraction. The overall fraction will be
in the range of [0, mRepeatCount + 1]. Both current iteration and fraction in the current
iteration can be derived from it.
/**
     * Calculates current iteration based on the overall fraction. The overall fraction will be
     * in the range of [0, mRepeatCount + 1]. Both current iteration and fraction in the current
     * iteration can be derived from it.
     */
    private int getCurrentIteration(float fraction) {
        fraction = clampFraction(fraction);
        // If the overall fraction is a positive integer, we consider the current iteration to be
        // complete. In other words, the fraction for the current iteration would be 1, and the
        // current iteration would be overall fraction - 1.
        double iteration = Math.floor(fraction);
        if (fraction == iteration && fraction > 0) {
            iteration--;
        }
        return (int) iteration;
    }

    
Calculates the fraction of the current iteration, taking into account whether the animation
should be played backwards. E.g. When the animation is played backwards in an iteration,
the fraction for that iteration will go from 1f to 0f.
/**
     * Calculates the fraction of the current iteration, taking into account whether the animation
     * should be played backwards. E.g. When the animation is played backwards in an iteration,
     * the fraction for that iteration will go from 1f to 0f.
     */
    private float getCurrentIterationFraction(float fraction, boolean inReverse) {
        fraction = clampFraction(fraction);
        int iteration = getCurrentIteration(fraction);
        float currentFraction = fraction - iteration;
        return shouldPlayBackward(iteration, inReverse) ? 1f - currentFraction : currentFraction;
    }

    
Clamps fraction into the correct range: [0, mRepeatCount + 1]. If repeat count is infinite,
no upper bound will be set for the fraction.
Params:
fraction – fraction to be clamped
Returns:
fraction clamped into the range of [0, mRepeatCount + 1]/**
     * Clamps fraction into the correct range: [0, mRepeatCount + 1]. If repeat count is infinite,
     * no upper bound will be set for the fraction.
     *
     * @param fraction fraction to be clamped
     * @return fraction clamped into the range of [0, mRepeatCount + 1]
     */
    private float clampFraction(float fraction) {
        if (fraction < 0) {
            fraction = 0;
        } else if (mRepeatCount != INFINITE) {
            fraction = Math.min(fraction, mRepeatCount + 1);
        }
        return fraction;
    }

    
Calculates the direction of animation playing (i.e. forward or backward), based on 1)
whether the entire animation is being reversed, 2) repeat mode applied to the current
iteration.
/**
     * Calculates the direction of animation playing (i.e. forward or backward), based on 1)
     * whether the entire animation is being reversed, 2) repeat mode applied to the current
     * iteration.
     */
    private boolean shouldPlayBackward(int iteration, boolean inReverse) {
        if (iteration > 0 && mRepeatMode == REVERSE &&
                (iteration < (mRepeatCount + 1) || mRepeatCount == INFINITE)) {
            // if we were seeked to some other iteration in a reversing animator,
            // figure out the correct direction to start playing based on the iteration
            if (inReverse) {
                return (iteration % 2) == 0;
            } else {
                return (iteration % 2) != 0;
            }
        } else {
            return inReverse;
        }
    }

    
Gets the current position of the animation in time, which is equal to the current time minus the time that the animation started. An animation that is not yet started will return a value of zero, unless the animation has has its play time set via setCurrentPlayTime(long) or setCurrentFraction(float), in which case it will return the time that was set. 
Returns:
The current position in time of the animation./**
     * Gets the current position of the animation in time, which is equal to the current
     * time minus the time that the animation started. An animation that is not yet started will
     * return a value of zero, unless the animation has has its play time set via
     * {@link #setCurrentPlayTime(long)} or {@link #setCurrentFraction(float)}, in which case
     * it will return the time that was set.
     *
     * @return The current position in time of the animation.
     */
    public long getCurrentPlayTime() {
        if (!mInitialized || (!mStarted && mSeekFraction < 0)) {
            return 0;
        }
        if (mSeekFraction >= 0) {
            return (long) (mDuration * mSeekFraction);
        }
        float durationScale = resolveDurationScale();
        if (durationScale == 0f) {
            durationScale = 1f;
        }
        return (long) ((AnimationUtils.currentAnimationTimeMillis() - mStartTime) / durationScale);
    }

    
The amount of time, in milliseconds, to delay starting the animation after start() is called. 
Returns:
the number of milliseconds to delay running the animation/**
     * The amount of time, in milliseconds, to delay starting the animation after
     * {@link #start()} is called.
     *
     * @return the number of milliseconds to delay running the animation
     */
    @Override
    public long getStartDelay() {
        return mStartDelay;
    }

    
The amount of time, in milliseconds, to delay starting the animation after start() is called. Note that the start delay should always be non-negative. Any negative start delay will be clamped to 0 on N and above. 
Params:
startDelay – The amount of the delay, in milliseconds/**
     * The amount of time, in milliseconds, to delay starting the animation after
     * {@link #start()} is called. Note that the start delay should always be non-negative. Any
     * negative start delay will be clamped to 0 on N and above.
     *
     * @param startDelay The amount of the delay, in milliseconds
     */
    @Override
    public void setStartDelay(long startDelay) {
        // Clamp start delay to non-negative range.
        if (startDelay < 0) {
            Log.w(TAG, "Start delay should always be non-negative");
            startDelay = 0;
        }
        mStartDelay = startDelay;
    }

    
The amount of time, in milliseconds, between each frame of the animation. This is a requested time that the animation will attempt to honor, but the actual delay between frames may be different, depending on system load and capabilities. This is a static function because the same delay will be applied to all animations, since they are all run off of a single timing loop. The frame delay may be ignored when the animation system uses an external timing source, such as the display refresh rate (vsync), to govern animations. Note that this method should be called from the same thread that start() is called in order to check the frame delay for that animation. A runtime exception will be thrown if the calling thread does not have a Looper. 
Returns:
the requested time between frames, in milliseconds/**
     * The amount of time, in milliseconds, between each frame of the animation. This is a
     * requested time that the animation will attempt to honor, but the actual delay between
     * frames may be different, depending on system load and capabilities. This is a static
     * function because the same delay will be applied to all animations, since they are all
     * run off of a single timing loop.
     *
     * The frame delay may be ignored when the animation system uses an external timing
     * source, such as the display refresh rate (vsync), to govern animations.
     *
     * Note that this method should be called from the same thread that {@link #start()} is
     * called in order to check the frame delay for that animation. A runtime exception will be
     * thrown if the calling thread does not have a Looper.
     *
     * @return the requested time between frames, in milliseconds
     */
    public static long getFrameDelay() {
        return AnimationHandler.getInstance().getFrameDelay();
    }

    
The amount of time, in milliseconds, between each frame of the animation. This is a requested time that the animation will attempt to honor, but the actual delay between frames may be different, depending on system load and capabilities. This is a static function because the same delay will be applied to all animations, since they are all run off of a single timing loop. The frame delay may be ignored when the animation system uses an external timing source, such as the display refresh rate (vsync), to govern animations. Note that this method should be called from the same thread that start() is called in order to have the new frame delay take effect on that animation. A runtime exception will be thrown if the calling thread does not have a Looper. 
Params:
frameDelay – the requested time between frames, in milliseconds/**
     * The amount of time, in milliseconds, between each frame of the animation. This is a
     * requested time that the animation will attempt to honor, but the actual delay between
     * frames may be different, depending on system load and capabilities. This is a static
     * function because the same delay will be applied to all animations, since they are all
     * run off of a single timing loop.
     *
     * The frame delay may be ignored when the animation system uses an external timing
     * source, such as the display refresh rate (vsync), to govern animations.
     *
     * Note that this method should be called from the same thread that {@link #start()} is
     * called in order to have the new frame delay take effect on that animation. A runtime
     * exception will be thrown if the calling thread does not have a Looper.
     *
     * @param frameDelay the requested time between frames, in milliseconds
     */
    public static void setFrameDelay(long frameDelay) {
        AnimationHandler.getInstance().setFrameDelay(frameDelay);
    }

    
The most recent value calculated by this ValueAnimator when there is just one
property being animated. This value is only sensible while the animation is running. The main
purpose for this read-only property is to retrieve the value from the ValueAnimator during a call to AnimatorUpdateListener.onAnimationUpdate(ValueAnimator), which is called during each animation frame, immediately after the value is calculated. 
Returns:
animatedValue The value most recently calculated by this ValueAnimator for
the single property being animated. If there are several properties being animated
(specified by several PropertyValuesHolder objects in the constructor), this function
returns the animated value for the first of those objects./**
     * The most recent value calculated by this <code>ValueAnimator</code> when there is just one
     * property being animated. This value is only sensible while the animation is running. The main
     * purpose for this read-only property is to retrieve the value from the <code>ValueAnimator</code>
     * during a call to {@link AnimatorUpdateListener#onAnimationUpdate(ValueAnimator)}, which
     * is called during each animation frame, immediately after the value is calculated.
     *
     * @return animatedValue The value most recently calculated by this <code>ValueAnimator</code> for
     * the single property being animated. If there are several properties being animated
     * (specified by several PropertyValuesHolder objects in the constructor), this function
     * returns the animated value for the first of those objects.
     */
    public Object getAnimatedValue() {
        if (mValues != null && mValues.length > 0) {
            return mValues[0].getAnimatedValue();
        }
        // Shouldn't get here; should always have values unless ValueAnimator was set up wrong
        return null;
    }

    
The most recent value calculated by this ValueAnimator for propertyName.
The main purpose for this read-only property is to retrieve the value from the
ValueAnimator during a call to AnimatorUpdateListener.onAnimationUpdate(ValueAnimator), which is called during each animation frame, immediately after the value is calculated. 
Returns:
animatedValue The value most recently calculated for the named property
by this ValueAnimator./**
     * The most recent value calculated by this <code>ValueAnimator</code> for <code>propertyName</code>.
     * The main purpose for this read-only property is to retrieve the value from the
     * <code>ValueAnimator</code> during a call to
     * {@link AnimatorUpdateListener#onAnimationUpdate(ValueAnimator)}, which
     * is called during each animation frame, immediately after the value is calculated.
     *
     * @return animatedValue The value most recently calculated for the named property
     * by this <code>ValueAnimator</code>.
     */
    public Object getAnimatedValue(String propertyName) {
        PropertyValuesHolder valuesHolder = mValuesMap.get(propertyName);
        if (valuesHolder != null) {
            return valuesHolder.getAnimatedValue();
        } else {
            // At least avoid crashing if called with bogus propertyName
            return null;
        }
    }

    
Sets how many times the animation should be repeated. If the repeat count is 0, the animation is never repeated. If the repeat count is greater than 0 or INFINITE, the repeat mode will be taken into account. The repeat count is 0 by default. 
Params:
value – the number of times the animation should be repeated/**
     * Sets how many times the animation should be repeated. If the repeat
     * count is 0, the animation is never repeated. If the repeat count is
     * greater than 0 or {@link #INFINITE}, the repeat mode will be taken
     * into account. The repeat count is 0 by default.
     *
     * @param value the number of times the animation should be repeated
     */
    public void setRepeatCount(int value) {
        mRepeatCount = value;
    }
    
Defines how many times the animation should repeat. The default value
is 0.
Returns:
the number of times the animation should repeat, or INFINITE/**
     * Defines how many times the animation should repeat. The default value
     * is 0.
     *
     * @return the number of times the animation should repeat, or {@link #INFINITE}
     */
    public int getRepeatCount() {
        return mRepeatCount;
    }

    
Defines what this animation should do when it reaches the end. This setting is applied only when the repeat count is either greater than 0 or INFINITE. Defaults to RESTART. 
Params:
value – RESTART or REVERSE/**
     * Defines what this animation should do when it reaches the end. This
     * setting is applied only when the repeat count is either greater than
     * 0 or {@link #INFINITE}. Defaults to {@link #RESTART}.
     *
     * @param value {@link #RESTART} or {@link #REVERSE}
     */
    public void setRepeatMode(@RepeatMode int value) {
        mRepeatMode = value;
    }

    
Defines what this animation should do when it reaches the end.
Returns:
either one of REVERSE or RESTART/**
     * Defines what this animation should do when it reaches the end.
     *
     * @return either one of {@link #REVERSE} or {@link #RESTART}
     */
    @RepeatMode
    public int getRepeatMode() {
        return mRepeatMode;
    }

    
Adds a listener to the set of listeners that are sent update events through the life of
an animation. This method is called on all listeners for every frame of the animation,
after the values for the animation have been calculated.
Params:
listener – the listener to be added to the current set of listeners for this animation./**
     * Adds a listener to the set of listeners that are sent update events through the life of
     * an animation. This method is called on all listeners for every frame of the animation,
     * after the values for the animation have been calculated.
     *
     * @param listener the listener to be added to the current set of listeners for this animation.
     */
    public void addUpdateListener(AnimatorUpdateListener listener) {
        if (mUpdateListeners == null) {
            mUpdateListeners = new ArrayList<AnimatorUpdateListener>();
        }
        mUpdateListeners.add(listener);
    }

    
Removes all listeners from the set listening to frame updates for this animation.
/**
     * Removes all listeners from the set listening to frame updates for this animation.
     */
    public void removeAllUpdateListeners() {
        if (mUpdateListeners == null) {
            return;
        }
        mUpdateListeners.clear();
        mUpdateListeners = null;
    }

    
Removes a listener from the set listening to frame updates for this animation.
Params:
listener – the listener to be removed from the current set of update listeners
for this animation./**
     * Removes a listener from the set listening to frame updates for this animation.
     *
     * @param listener the listener to be removed from the current set of update listeners
     * for this animation.
     */
    public void removeUpdateListener(AnimatorUpdateListener listener) {
        if (mUpdateListeners == null) {
            return;
        }
        mUpdateListeners.remove(listener);
        if (mUpdateListeners.size() == 0) {
            mUpdateListeners = null;
        }
    }


    
The time interpolator used in calculating the elapsed fraction of this animation. The interpolator determines whether the animation runs with linear or non-linear motion, such as acceleration and deceleration. The default value is AccelerateDecelerateInterpolator 
Params:
value – the interpolator to be used by this animation. A value of null
will result in linear interpolation./**
     * The time interpolator used in calculating the elapsed fraction of this animation. The
     * interpolator determines whether the animation runs with linear or non-linear motion,
     * such as acceleration and deceleration. The default value is
     * {@link android.view.animation.AccelerateDecelerateInterpolator}
     *
     * @param value the interpolator to be used by this animation. A value of <code>null</code>
     * will result in linear interpolation.
     */
    @Override
    public void setInterpolator(TimeInterpolator value) {
        if (value != null) {
            mInterpolator = value;
        } else {
            mInterpolator = new LinearInterpolator();
        }
    }

    
Returns the timing interpolator that this ValueAnimator uses.
Returns:
The timing interpolator for this ValueAnimator./**
     * Returns the timing interpolator that this ValueAnimator uses.
     *
     * @return The timing interpolator for this ValueAnimator.
     */
    @Override
    public TimeInterpolator getInterpolator() {
        return mInterpolator;
    }

    
The type evaluator to be used when calculating the animated values of this animation.
The system will automatically assign a float or int evaluator based on the type
of startValue and endValue in the constructor. But if these values are not one of these primitive types, or if different evaluation is desired (such as is necessary with int values that represent colors), a custom evaluator needs to be assigned. For example, when running an animation on color values, the ArgbEvaluator should be used to get correct RGB color interpolation. 
If this ValueAnimator has only one set of values being animated between, this evaluator
will be used for that set. If there are several sets of values being animated, which is
the case if PropertyValuesHolder objects were set on the ValueAnimator, then the evaluator
is assigned just to the first PropertyValuesHolder object.
Params:
value – the evaluator to be used this animation/**
     * The type evaluator to be used when calculating the animated values of this animation.
     * The system will automatically assign a float or int evaluator based on the type
     * of <code>startValue</code> and <code>endValue</code> in the constructor. But if these values
     * are not one of these primitive types, or if different evaluation is desired (such as is
     * necessary with int values that represent colors), a custom evaluator needs to be assigned.
     * For example, when running an animation on color values, the {@link ArgbEvaluator}
     * should be used to get correct RGB color interpolation.
     *
     * <p>If this ValueAnimator has only one set of values being animated between, this evaluator
     * will be used for that set. If there are several sets of values being animated, which is
     * the case if PropertyValuesHolder objects were set on the ValueAnimator, then the evaluator
     * is assigned just to the first PropertyValuesHolder object.</p>
     *
     * @param value the evaluator to be used this animation
     */
    public void setEvaluator(TypeEvaluator value) {
        if (value != null && mValues != null && mValues.length > 0) {
            mValues[0].setEvaluator(value);
        }
    }

    private void notifyStartListeners() {
        if (mListeners != null && !mStartListenersCalled) {
            ArrayList<AnimatorListener> tmpListeners =
                    (ArrayList<AnimatorListener>) mListeners.clone();
            int numListeners = tmpListeners.size();
            for (int i = 0; i < numListeners; ++i) {
                tmpListeners.get(i).onAnimationStart(this, mReversing);
            }
        }
        mStartListenersCalled = true;
    }

    
Start the animation playing. This version of start() takes a boolean flag that indicates
whether the animation should play in reverse. The flag is usually false, but may be set
to true if called from the reverse() method.
The animation started by calling this method will be run on the thread that called
this method. This thread should have a Looper on it (a runtime exception will be thrown if
this is not the case). Also, if the animation will animate
properties of objects in the view hierarchy, then the calling thread should be the UI
thread for that view hierarchy.
Params:
playBackwards – Whether the ValueAnimator should start playing in reverse./**
     * Start the animation playing. This version of start() takes a boolean flag that indicates
     * whether the animation should play in reverse. The flag is usually false, but may be set
     * to true if called from the reverse() method.
     *
     * <p>The animation started by calling this method will be run on the thread that called
     * this method. This thread should have a Looper on it (a runtime exception will be thrown if
     * this is not the case). Also, if the animation will animate
     * properties of objects in the view hierarchy, then the calling thread should be the UI
     * thread for that view hierarchy.</p>
     *
     * @param playBackwards Whether the ValueAnimator should start playing in reverse.
     */
    private void start(boolean playBackwards) {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }
        mReversing = playBackwards;
        mSelfPulse = !mSuppressSelfPulseRequested;
        // Special case: reversing from seek-to-0 should act as if not seeked at all.
        if (playBackwards && mSeekFraction != -1 && mSeekFraction != 0) {
            if (mRepeatCount == INFINITE) {
                // Calculate the fraction of the current iteration.
                float fraction = (float) (mSeekFraction - Math.floor(mSeekFraction));
                mSeekFraction = 1 - fraction;
            } else {
                mSeekFraction = 1 + mRepeatCount - mSeekFraction;
            }
        }
        mStarted = true;
        mPaused = false;
        mRunning = false;
        mAnimationEndRequested = false;
        // Resets mLastFrameTime when start() is called, so that if the animation was running,
        // calling start() would put the animation in the
        // started-but-not-yet-reached-the-first-frame phase.
        mLastFrameTime = -1;
        mFirstFrameTime = -1;
        mStartTime = -1;
        addAnimationCallback(0);

        if (mStartDelay == 0 || mSeekFraction >= 0 || mReversing) {
            // If there's no start delay, init the animation and notify start listeners right away
            // to be consistent with the previous behavior. Otherwise, postpone this until the first
            // frame after the start delay.
            startAnimation();
            if (mSeekFraction == -1) {
                // No seek, start at play time 0. Note that the reason we are not using fraction 0
                // is because for animations with 0 duration, we want to be consistent with pre-N
                // behavior: skip to the final value immediately.
                setCurrentPlayTime(0);
            } else {
                setCurrentFraction(mSeekFraction);
            }
        }
    }

    void startWithoutPulsing(boolean inReverse) {
        mSuppressSelfPulseRequested = true;
        if (inReverse) {
            reverse();
        } else {
            start();
        }
        mSuppressSelfPulseRequested = false;
    }

    @Override
    public void start() {
        start(false);
    }

    @Override
    public void cancel() {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }

        // If end has already been requested, through a previous end() or cancel() call, no-op
        // until animation starts again.
        if (mAnimationEndRequested) {
            return;
        }

        // Only cancel if the animation is actually running or has been started and is about
        // to run
        // Only notify listeners if the animator has actually started
        if ((mStarted || mRunning) && mListeners != null) {
            if (!mRunning) {
                // If it's not yet running, then start listeners weren't called. Call them now.
                notifyStartListeners();
            }
            ArrayList<AnimatorListener> tmpListeners =
                    (ArrayList<AnimatorListener>) mListeners.clone();
            for (AnimatorListener listener : tmpListeners) {
                listener.onAnimationCancel(this);
            }
        }
        endAnimation();

    }

    @Override
    public void end() {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }
        if (!mRunning) {
            // Special case if the animation has not yet started; get it ready for ending
            startAnimation();
            mStarted = true;
        } else if (!mInitialized) {
            initAnimation();
        }
        animateValue(shouldPlayBackward(mRepeatCount, mReversing) ? 0f : 1f);
        endAnimation();
    }

    @Override
    public void resume() {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be resumed from the same " +
                    "thread that the animator was started on");
        }
        if (mPaused && !mResumed) {
            mResumed = true;
            if (mPauseTime > 0) {
                addAnimationCallback(0);
            }
        }
        super.resume();
    }

    @Override
    public void pause() {
        boolean previouslyPaused = mPaused;
        super.pause();
        if (!previouslyPaused && mPaused) {
            mPauseTime = -1;
            mResumed = false;
        }
    }

    @Override
    public boolean isRunning() {
        return mRunning;
    }

    @Override
    public boolean isStarted() {
        return mStarted;
    }

    
Plays the ValueAnimator in reverse. If the animation is already running,
it will stop itself and play backwards from the point reached when reverse was called.
If the animation is not currently running, then it will start from the end and
play backwards. This behavior is only set for the current animation; future playing
of the animation will use the default behavior of playing forward.
/**
     * Plays the ValueAnimator in reverse. If the animation is already running,
     * it will stop itself and play backwards from the point reached when reverse was called.
     * If the animation is not currently running, then it will start from the end and
     * play backwards. This behavior is only set for the current animation; future playing
     * of the animation will use the default behavior of playing forward.
     */
    @Override
    public void reverse() {
        if (isPulsingInternal()) {
            long currentTime = AnimationUtils.currentAnimationTimeMillis();
            long currentPlayTime = currentTime - mStartTime;
            long timeLeft = getScaledDuration() - currentPlayTime;
            mStartTime = currentTime - timeLeft;
            mStartTimeCommitted = true; // do not allow start time to be compensated for jank
            mReversing = !mReversing;
        } else if (mStarted) {
            mReversing = !mReversing;
            end();
        } else {
            start(true);
        }
    }

    
@hide
/**
     * @hide
     */
    @Override
    public boolean canReverse() {
        return true;
    }

    
Called internally to end an animation by removing it from the animations list. Must be
called on the UI thread.
/**
     * Called internally to end an animation by removing it from the animations list. Must be
     * called on the UI thread.
     */
    private void endAnimation() {
        if (mAnimationEndRequested) {
            return;
        }
        removeAnimationCallback();

        mAnimationEndRequested = true;
        mPaused = false;
        boolean notify = (mStarted || mRunning) && mListeners != null;
        if (notify && !mRunning) {
            // If it's not yet running, then start listeners weren't called. Call them now.
            notifyStartListeners();
        }
        mRunning = false;
        mStarted = false;
        mStartListenersCalled = false;
        mLastFrameTime = -1;
        mFirstFrameTime = -1;
        mStartTime = -1;
        if (notify && mListeners != null) {
            ArrayList<AnimatorListener> tmpListeners =
                    (ArrayList<AnimatorListener>) mListeners.clone();
            int numListeners = tmpListeners.size();
            for (int i = 0; i < numListeners; ++i) {
                tmpListeners.get(i).onAnimationEnd(this, mReversing);
            }
        }
        // mReversing needs to be reset *after* notifying the listeners for the end callbacks.
        mReversing = false;
        if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
            Trace.asyncTraceEnd(Trace.TRACE_TAG_VIEW, getNameForTrace(),
                    System.identityHashCode(this));
        }
    }

    
Called internally to start an animation by adding it to the active animations list. Must be
called on the UI thread.
/**
     * Called internally to start an animation by adding it to the active animations list. Must be
     * called on the UI thread.
     */
    private void startAnimation() {
        if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
            Trace.asyncTraceBegin(Trace.TRACE_TAG_VIEW, getNameForTrace(),
                    System.identityHashCode(this));
        }

        mAnimationEndRequested = false;
        initAnimation();
        mRunning = true;
        if (mSeekFraction >= 0) {
            mOverallFraction = mSeekFraction;
        } else {
            mOverallFraction = 0f;
        }
        if (mListeners != null) {
            notifyStartListeners();
        }
    }

    
Internal only: This tracks whether the animation has gotten on the animation loop. Note this is different than isRunning() in that the latter tracks the time after start() is called (or after start delay if any), which may be before the animation loop starts. /**
     * Internal only: This tracks whether the animation has gotten on the animation loop. Note
     * this is different than {@link #isRunning()} in that the latter tracks the time after start()
     * is called (or after start delay if any), which may be before the animation loop starts.
     */
    private boolean isPulsingInternal() {
        return mLastFrameTime >= 0;
    }

    
Returns the name of this animator for debugging purposes.
/**
     * Returns the name of this animator for debugging purposes.
     */
    String getNameForTrace() {
        return "animator";
    }

    
Applies an adjustment to the animation to compensate for jank between when
the animation first ran and when the frame was drawn.
@hide
/**
     * Applies an adjustment to the animation to compensate for jank between when
     * the animation first ran and when the frame was drawn.
     * @hide
     */
    public void commitAnimationFrame(long frameTime) {
        if (!mStartTimeCommitted) {
            mStartTimeCommitted = true;
            long adjustment = frameTime - mLastFrameTime;
            if (adjustment > 0) {
                mStartTime += adjustment;
                if (DEBUG) {
                    Log.d(TAG, "Adjusted start time by " + adjustment + " ms: " + toString());
                }
            }
        }
    }

    
This internal function processes a single animation frame for a given animation. The
currentTime parameter is the timing pulse sent by the handler, used to calculate the
elapsed duration, and therefore
the elapsed fraction, of the animation. The return value indicates whether the animation
should be ended (which happens when the elapsed time of the animation exceeds the
animation's duration, including the repeatCount).
Params:
currentTime – The current time, as tracked by the static timing handler
Returns:
true if the animation's duration, including any repetitions due to
repeatCount has been exceeded and the animation should be ended./**
     * This internal function processes a single animation frame for a given animation. The
     * currentTime parameter is the timing pulse sent by the handler, used to calculate the
     * elapsed duration, and therefore
     * the elapsed fraction, of the animation. The return value indicates whether the animation
     * should be ended (which happens when the elapsed time of the animation exceeds the
     * animation's duration, including the repeatCount).
     *
     * @param currentTime The current time, as tracked by the static timing handler
     * @return true if the animation's duration, including any repetitions due to
     * <code>repeatCount</code> has been exceeded and the animation should be ended.
     */
    boolean animateBasedOnTime(long currentTime) {
        boolean done = false;
        if (mRunning) {
            final long scaledDuration = getScaledDuration();
            final float fraction = scaledDuration > 0 ?
                    (float)(currentTime - mStartTime) / scaledDuration : 1f;
            final float lastFraction = mOverallFraction;
            final boolean newIteration = (int) fraction > (int) lastFraction;
            final boolean lastIterationFinished = (fraction >= mRepeatCount + 1) &&
                    (mRepeatCount != INFINITE);
            if (scaledDuration == 0) {
                // 0 duration animator, ignore the repeat count and skip to the end
                done = true;
            } else if (newIteration && !lastIterationFinished) {
                // Time to repeat
                if (mListeners != null) {
                    int numListeners = mListeners.size();
                    for (int i = 0; i < numListeners; ++i) {
                        mListeners.get(i).onAnimationRepeat(this);
                    }
                }
            } else if (lastIterationFinished) {
                done = true;
            }
            mOverallFraction = clampFraction(fraction);
            float currentIterationFraction = getCurrentIterationFraction(
                    mOverallFraction, mReversing);
            animateValue(currentIterationFraction);
        }
        return done;
    }

    
Internal use only. This method does not modify any fields of the animation. It should be called when seeking in an AnimatorSet. When the last play time and current play time are of different repeat iterations, AnimationListener.onAnimationRepeat(Animation) will be called. /**
     * Internal use only.
     *
     * This method does not modify any fields of the animation. It should be called when seeking
     * in an AnimatorSet. When the last play time and current play time are of different repeat
     * iterations,
     * {@link android.view.animation.Animation.AnimationListener#onAnimationRepeat(Animation)}
     * will be called.
     */
    @Override
    void animateBasedOnPlayTime(long currentPlayTime, long lastPlayTime, boolean inReverse) {
        if (currentPlayTime < 0 || lastPlayTime < 0) {
            throw new UnsupportedOperationException("Error: Play time should never be negative.");
        }

        initAnimation();
        // Check whether repeat callback is needed only when repeat count is non-zero
        if (mRepeatCount > 0) {
            int iteration = (int) (currentPlayTime / mDuration);
            int lastIteration = (int) (lastPlayTime / mDuration);

            // Clamp iteration to [0, mRepeatCount]
            iteration = Math.min(iteration, mRepeatCount);
            lastIteration = Math.min(lastIteration, mRepeatCount);

            if (iteration != lastIteration) {
                if (mListeners != null) {
                    int numListeners = mListeners.size();
                    for (int i = 0; i < numListeners; ++i) {
                        mListeners.get(i).onAnimationRepeat(this);
                    }
                }
            }
        }

        if (mRepeatCount != INFINITE && currentPlayTime >= (mRepeatCount + 1) * mDuration) {
            skipToEndValue(inReverse);
        } else {
            // Find the current fraction:
            float fraction = currentPlayTime / (float) mDuration;
            fraction = getCurrentIterationFraction(fraction, inReverse);
            animateValue(fraction);
        }
    }

    
Internal use only.
Skips the animation value to end/start, depending on whether the play direction is forward
or backward.
Params:
inReverse – whether the end value is based on a reverse direction. If yes, this is
                 equivalent to skip to start value in a forward playing direction./**
     * Internal use only.
     * Skips the animation value to end/start, depending on whether the play direction is forward
     * or backward.
     *
     * @param inReverse whether the end value is based on a reverse direction. If yes, this is
     *                  equivalent to skip to start value in a forward playing direction.
     */
    void skipToEndValue(boolean inReverse) {
        initAnimation();
        float endFraction = inReverse ? 0f : 1f;
        if (mRepeatCount % 2 == 1 && mRepeatMode == REVERSE) {
            // This would end on fraction = 0
            endFraction = 0f;
        }
        animateValue(endFraction);
    }

    @Override
    boolean isInitialized() {
        return mInitialized;
    }

    
Processes a frame of the animation, adjusting the start time if needed.
Params:
frameTime – The frame time.
Returns:
true if the animation has ended.
@hide
/**
     * Processes a frame of the animation, adjusting the start time if needed.
     *
     * @param frameTime The frame time.
     * @return true if the animation has ended.
     * @hide
     */
    public final boolean doAnimationFrame(long frameTime) {
        if (mStartTime < 0) {
            // First frame. If there is start delay, start delay count down will happen *after* this
            // frame.
            mStartTime = mReversing
                    ? frameTime
                    : frameTime + (long) (mStartDelay * resolveDurationScale());
        }

        // Handle pause/resume
        if (mPaused) {
            mPauseTime = frameTime;
            removeAnimationCallback();
            return false;
        } else if (mResumed) {
            mResumed = false;
            if (mPauseTime > 0) {
                // Offset by the duration that the animation was paused
                mStartTime += (frameTime - mPauseTime);
            }
        }

        if (!mRunning) {
            // If not running, that means the animation is in the start delay phase of a forward
            // running animation. In the case of reversing, we want to run start delay in the end.
            if (mStartTime > frameTime && mSeekFraction == -1) {
                // This is when no seek fraction is set during start delay. If developers change the
                // seek fraction during the delay, animation will start from the seeked position
                // right away.
                return false;
            } else {
                // If mRunning is not set by now, that means non-zero start delay,
                // no seeking, not reversing. At this point, start delay has passed.
                mRunning = true;
                startAnimation();
            }
        }

        if (mLastFrameTime < 0) {
            if (mSeekFraction >= 0) {
                long seekTime = (long) (getScaledDuration() * mSeekFraction);
                mStartTime = frameTime - seekTime;
                mSeekFraction = -1;
            }
            mStartTimeCommitted = false; // allow start time to be compensated for jank
        }
        mLastFrameTime = frameTime;
        // The frame time might be before the start time during the first frame of
        // an animation.  The "current time" must always be on or after the start
        // time to avoid animating frames at negative time intervals.  In practice, this
        // is very rare and only happens when seeking backwards.
        final long currentTime = Math.max(frameTime, mStartTime);
        boolean finished = animateBasedOnTime(currentTime);

        if (finished) {
            endAnimation();
        }
        return finished;
    }

    @Override
    boolean pulseAnimationFrame(long frameTime) {
        if (mSelfPulse) {
            // Pulse animation frame will *always* be after calling start(). If mSelfPulse isn't
            // set to false at this point, that means child animators did not call super's start().
            // This can happen when the Animator is just a non-animating wrapper around a real
            // functional animation. In this case, we can't really pulse a frame into the animation,
            // because the animation cannot necessarily be properly initialized (i.e. no start/end
            // values set).
            return false;
        }
        return doAnimationFrame(frameTime);
    }

    private void addOneShotCommitCallback() {
        if (!mSelfPulse) {
            return;
        }
        getAnimationHandler().addOneShotCommitCallback(this);
    }

    private void removeAnimationCallback() {
        if (!mSelfPulse) {
            return;
        }
        getAnimationHandler().removeCallback(this);
    }

    private void addAnimationCallback(long delay) {
        if (!mSelfPulse) {
            return;
        }
        getAnimationHandler().addAnimationFrameCallback(this, delay);
    }

    
Returns the current animation fraction, which is the elapsed/interpolated fraction used in
the most recent frame update on the animation.
Returns:
Elapsed/interpolated fraction of the animation./**
     * Returns the current animation fraction, which is the elapsed/interpolated fraction used in
     * the most recent frame update on the animation.
     *
     * @return Elapsed/interpolated fraction of the animation.
     */
    public float getAnimatedFraction() {
        return mCurrentFraction;
    }

    
This method is called with the elapsed fraction of the animation during every
animation frame. This function turns the elapsed fraction into an interpolated fraction
and then into an animated value (from the evaluator. The function is called mostly during
animation updates, but it is also called when the end()
function is called, to set the final value on the property.
Overrides of this method must call the superclass to perform the calculation
of the animated value.
Params:
fraction – The elapsed fraction of the animation./**
     * This method is called with the elapsed fraction of the animation during every
     * animation frame. This function turns the elapsed fraction into an interpolated fraction
     * and then into an animated value (from the evaluator. The function is called mostly during
     * animation updates, but it is also called when the <code>end()</code>
     * function is called, to set the final value on the property.
     *
     * <p>Overrides of this method must call the superclass to perform the calculation
     * of the animated value.</p>
     *
     * @param fraction The elapsed fraction of the animation.
     */
    @CallSuper
    void animateValue(float fraction) {
        fraction = mInterpolator.getInterpolation(fraction);
        mCurrentFraction = fraction;
        int numValues = mValues.length;
        for (int i = 0; i < numValues; ++i) {
            mValues[i].calculateValue(fraction);
        }
        if (mUpdateListeners != null) {
            int numListeners = mUpdateListeners.size();
            for (int i = 0; i < numListeners; ++i) {
                mUpdateListeners.get(i).onAnimationUpdate(this);
            }
        }
    }

    @Override
    public ValueAnimator clone() {
        final ValueAnimator anim = (ValueAnimator) super.clone();
        if (mUpdateListeners != null) {
            anim.mUpdateListeners = new ArrayList<AnimatorUpdateListener>(mUpdateListeners);
        }
        anim.mSeekFraction = -1;
        anim.mReversing = false;
        anim.mInitialized = false;
        anim.mStarted = false;
        anim.mRunning = false;
        anim.mPaused = false;
        anim.mResumed = false;
        anim.mStartListenersCalled = false;
        anim.mStartTime = -1;
        anim.mStartTimeCommitted = false;
        anim.mAnimationEndRequested = false;
        anim.mPauseTime = -1;
        anim.mLastFrameTime = -1;
        anim.mFirstFrameTime = -1;
        anim.mOverallFraction = 0;
        anim.mCurrentFraction = 0;
        anim.mSelfPulse = true;
        anim.mSuppressSelfPulseRequested = false;

        PropertyValuesHolder[] oldValues = mValues;
        if (oldValues != null) {
            int numValues = oldValues.length;
            anim.mValues = new PropertyValuesHolder[numValues];
            anim.mValuesMap = new HashMap<String, PropertyValuesHolder>(numValues);
            for (int i = 0; i < numValues; ++i) {
                PropertyValuesHolder newValuesHolder = oldValues[i].clone();
                anim.mValues[i] = newValuesHolder;
                anim.mValuesMap.put(newValuesHolder.getPropertyName(), newValuesHolder);
            }
        }
        return anim;
    }

    
Implementors of this interface can add themselves as update listeners
to an ValueAnimator instance to receive callbacks on every animation
frame, after the current frame's values have been calculated for that
ValueAnimator.
/**
     * Implementors of this interface can add themselves as update listeners
     * to an <code>ValueAnimator</code> instance to receive callbacks on every animation
     * frame, after the current frame's values have been calculated for that
     * <code>ValueAnimator</code>.
     */
    public static interface AnimatorUpdateListener {
        
Notifies the occurrence of another frame of the animation.
Params:
animation – The animation which was repeated./**
         * <p>Notifies the occurrence of another frame of the animation.</p>
         *
         * @param animation The animation which was repeated.
         */
        void onAnimationUpdate(ValueAnimator animation);

    }

    
Return the number of animations currently running.
Used by StrictMode internally to annotate violations.
May be called on arbitrary threads!
@hide
/**
     * Return the number of animations currently running.
     *
     * Used by StrictMode internally to annotate violations.
     * May be called on arbitrary threads!
     *
     * @hide
     */
    public static int getCurrentAnimationsCount() {
        return AnimationHandler.getAnimationCount();
    }

    @Override
    public String toString() {
        String returnVal = "ValueAnimator@" + Integer.toHexString(hashCode());
        if (mValues != null) {
            for (int i = 0; i < mValues.length; ++i) {
                returnVal += "\n    " + mValues[i].toString();
            }
        }
        return returnVal;
    }

    
Whether or not the ValueAnimator is allowed to run asynchronously off of the UI thread. This is a hint that informs the ValueAnimator that it is OK to run the animation off-thread, however ValueAnimator may decide that it must run the animation on the UI thread anyway. For example if there is an AnimatorUpdateListener the animation will run on the UI thread, regardless of the value of this hint.
Regardless of whether or not the animation runs asynchronously, all
listener callbacks will be called on the UI thread.
To be able to use this hint the following must be true:

getAnimatedFraction() is not needed (it will return undefined values).
The animator is immutable while isStarted() is true. Requests to change values, duration, delay, etc... may be ignored.
Lifecycle callback events may be asynchronous. Events such as AnimatorListener.onAnimationEnd(Animator) or AnimatorListener.onAnimationRepeat(Animator) may end up delayed as they must be posted back to the UI thread, and any actions performed by those callbacks (such as starting new animations) will not happen in the same frame.
State change requests (cancel(), end(), reverse(), etc...) may be asynchronous. It is guaranteed that all state changes that are performed on the UI thread in the same frame will be applied as a single atomic update, however that frame may be the current frame, the next frame, or some future frame. This will also impact the observed state of the Animator. For example, isStarted() may still return true after a call to end(). Using the lifecycle callbacks is preferred over queries to isStarted(), isRunning(), and Animator.isPaused() for this reason.

@hide
/**
     * <p>Whether or not the ValueAnimator is allowed to run asynchronously off of
     * the UI thread. This is a hint that informs the ValueAnimator that it is
     * OK to run the animation off-thread, however ValueAnimator may decide
     * that it must run the animation on the UI thread anyway. For example if there
     * is an {@link AnimatorUpdateListener} the animation will run on the UI thread,
     * regardless of the value of this hint.</p>
     *
     * <p>Regardless of whether or not the animation runs asynchronously, all
     * listener callbacks will be called on the UI thread.</p>
     *
     * <p>To be able to use this hint the following must be true:</p>
     * <ol>
     * <li>{@link #getAnimatedFraction()} is not needed (it will return undefined values).</li>
     * <li>The animator is immutable while {@link #isStarted()} is true. Requests
     *    to change values, duration, delay, etc... may be ignored.</li>
     * <li>Lifecycle callback events may be asynchronous. Events such as
     *    {@link Animator.AnimatorListener#onAnimationEnd(Animator)} or
     *    {@link Animator.AnimatorListener#onAnimationRepeat(Animator)} may end up delayed
     *    as they must be posted back to the UI thread, and any actions performed
     *    by those callbacks (such as starting new animations) will not happen
     *    in the same frame.</li>
     * <li>State change requests ({@link #cancel()}, {@link #end()}, {@link #reverse()}, etc...)
     *    may be asynchronous. It is guaranteed that all state changes that are
     *    performed on the UI thread in the same frame will be applied as a single
     *    atomic update, however that frame may be the current frame,
     *    the next frame, or some future frame. This will also impact the observed
     *    state of the Animator. For example, {@link #isStarted()} may still return true
     *    after a call to {@link #end()}. Using the lifecycle callbacks is preferred over
     *    queries to {@link #isStarted()}, {@link #isRunning()}, and {@link #isPaused()}
     *    for this reason.</li>
     * </ol>
     * @hide
     */
    @Override
    public void setAllowRunningAsynchronously(boolean mayRunAsync) {
        // It is up to subclasses to support this, if they can.
    }

    
Returns:
The AnimationHandler that will be used to schedule updates for this animator.
@hide
/**
     * @return The {@link AnimationHandler} that will be used to schedule updates for this animator.
     * @hide
     */
    public AnimationHandler getAnimationHandler() {
        return AnimationHandler.getInstance();
    }
}