/*
 * 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.app.ActivityThread;
import android.app.Application;
import android.os.Build;
import android.os.Looper;
import android.util.AndroidRuntimeException;
import android.util.ArrayMap;
import android.util.Log;
import android.view.animation.Animation;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;

This class plays a set of Animator objects in the specified order. Animations can be set up to play together, in sequence, or after a specified delay. 
There are two different approaches to adding animations to a AnimatorSet: either the playTogether() or playSequentially() methods can be called to add a set of animations all at once, or the play(Animator) can be used in conjunction with methods in the Builder class to add animations one by one.
It is possible to set up a AnimatorSet with circular dependencies between
its animations. For example, an animation a1 could be set up to start before animation a2, a2
before a3, and a3 before a1. The results of this configuration are undefined, but will typically
result in none of the affected animations being played. Because of this (and because
circular dependencies do not make logical sense anyway), circular dependencies
should be avoided, and the dependency flow of animations should only be in one direction.

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

/**
 * This class plays a set of {@link Animator} objects in the specified order. Animations
 * can be set up to play together, in sequence, or after a specified delay.
 *
 * <p>There are two different approaches to adding animations to a <code>AnimatorSet</code>:
 * either the {@link AnimatorSet#playTogether(Animator[]) playTogether()} or
 * {@link AnimatorSet#playSequentially(Animator[]) playSequentially()} methods can be called to add
 * a set of animations all at once, or the {@link AnimatorSet#play(Animator)} can be
 * used in conjunction with methods in the {@link AnimatorSet.Builder Builder}
 * class to add animations
 * one by one.</p>
 *
 * <p>It is possible to set up a <code>AnimatorSet</code> with circular dependencies between
 * its animations. For example, an animation a1 could be set up to start before animation a2, a2
 * before a3, and a3 before a1. The results of this configuration are undefined, but will typically
 * result in none of the affected animations being played. Because of this (and because
 * circular dependencies do not make logical sense anyway), circular dependencies
 * should be avoided, and the dependency flow of animations should only be in one direction.
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 * <p>For more information about animating with {@code AnimatorSet}, read the
 * <a href="{@docRoot}guide/topics/graphics/prop-animation.html#choreography">Property
 * Animation</a> developer guide.</p>
 * </div>
 */
public final class AnimatorSet extends Animator implements AnimationHandler.AnimationFrameCallback {

    private static final String TAG = "AnimatorSet";
    /**
     * 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.
     */

    
Tracks animations currently being played, so that we know what to
cancel or end when cancel() or end() is called on this AnimatorSet
/**
     * Tracks animations currently being played, so that we know what to
     * cancel or end when cancel() or end() is called on this AnimatorSet
     */
    private ArrayList<Node> mPlayingSet = new ArrayList<Node>();

    
Contains all nodes, mapped to their respective Animators. When new
dependency information is added for an Animator, we want to add it
to a single node representing that Animator, not create a new Node
if one already exists.
/**
     * Contains all nodes, mapped to their respective Animators. When new
     * dependency information is added for an Animator, we want to add it
     * to a single node representing that Animator, not create a new Node
     * if one already exists.
     */
    private ArrayMap<Animator, Node> mNodeMap = new ArrayMap<Animator, Node>();

    
Contains the start and end events of all the nodes. All these events are sorted in this list.
/**
     * Contains the start and end events of all the nodes. All these events are sorted in this list.
     */
    private ArrayList<AnimationEvent> mEvents = new ArrayList<>();

    
Set of all nodes created for this AnimatorSet. This list is used upon
starting the set, and the nodes are placed in sorted order into the
sortedNodes collection.
/**
     * Set of all nodes created for this AnimatorSet. This list is used upon
     * starting the set, and the nodes are placed in sorted order into the
     * sortedNodes collection.
     */
    private ArrayList<Node> mNodes = new ArrayList<Node>();

    
Tracks whether any change has been made to the AnimatorSet, which is then used to
determine whether the dependency graph should be re-constructed.
/**
     * Tracks whether any change has been made to the AnimatorSet, which is then used to
     * determine whether the dependency graph should be re-constructed.
     */
    private boolean mDependencyDirty = false;

    
Indicates whether an AnimatorSet has been start()'d, whether or
not there is a nonzero startDelay.
/**
     * Indicates whether an AnimatorSet has been start()'d, whether or
     * not there is a nonzero startDelay.
     */
    private boolean mStarted = false;

    // The amount of time in ms to delay starting the animation after start() is called
    private long mStartDelay = 0;

    // Animator used for a nonzero startDelay
    private ValueAnimator mDelayAnim = ValueAnimator.ofFloat(0f, 1f).setDuration(0);

    // Root of the dependency tree of all the animators in the set. In this tree, parent-child
    // relationship captures the order of animation (i.e. parent and child will play sequentially),
    // and sibling relationship indicates "with" relationship, as sibling animators start at the
    // same time.
    private Node mRootNode = new Node(mDelayAnim);

    // How long the child animations should last in ms. The default value is negative, which
    // simply means that there is no duration set on the AnimatorSet. When a real duration is
    // set, it is passed along to the child animations.
    private long mDuration = -1;

    // Records the interpolator for the set. Null value indicates that no interpolator
    // was set on this AnimatorSet, so it should not be passed down to the children.
    private TimeInterpolator mInterpolator = null;

    // The total duration of finishing all the Animators in the set.
    private long mTotalDuration = 0;

    // In pre-N releases, calling end() before start() on an animator set is no-op. But that is not
    // consistent with the behavior for other animator types. In order to keep the behavior
    // consistent within Animation framework, when end() is called without start(), we will start
    // the animator set and immediately end it for N and forward.
    private final boolean mShouldIgnoreEndWithoutStart;

    // In pre-O releases, calling start() doesn't reset all the animators values to start values.
    // As a result, the start of the animation is inconsistent with what setCurrentPlayTime(0) would
    // look like on O. Also it is inconsistent with what reverse() does on O, as reverse would
    // advance all the animations to the right beginning values for before starting to reverse.
    // From O and forward, we will add an additional step of resetting the animation values (unless
    // the animation was previously seeked and therefore doesn't start from the beginning).
    private final boolean mShouldResetValuesAtStart;

    // In pre-O releases, end() may never explicitly called on a child animator. As a result, end()
    // may not even be properly implemented in a lot of cases. After a few apps crashing on this,
    // it became necessary to use an sdk target guard for calling end().
    private final boolean mEndCanBeCalled;

    // The time, in milliseconds, when last frame of the animation came in. -1 when the animation is
    // not running.
    private long mLastFrameTime = -1;

    // The time, in milliseconds, when the first frame of the animation came in. This is the
    // frame before we start counting down the start delay, if any.
    // -1 when the animation is not running.
    private long mFirstFrame = -1;

    // The time, in milliseconds, when the first frame of the animation came in.
    // -1 when the animation is not running.
    private int mLastEventId = -1;

    // Indicates whether the animation is reversing.
    private boolean mReversing = false;

    // Indicates whether the animation should register frame callbacks. If false, the animation will
    // passively wait for an AnimatorSet to pulse it.
    private boolean mSelfPulse = true;

    // SeekState stores the last seeked play time as well as seek direction.
    private SeekState mSeekState = new SeekState();

    // Indicates where children animators are all initialized with their start values captured.
    private boolean mChildrenInitialized = false;

    
Set on the next frame after pause() is called, used to calculate a new startTime
or delayStartTime which allows the animator set 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 set to continue from the point at which
     * it was paused. If negative, has not yet been set.
     */
    private long mPauseTime = -1;

    // This is to work around a bug in b/34736819. This needs to be removed once app team
    // fixes their side.
    private AnimatorListenerAdapter mDummyListener = new AnimatorListenerAdapter() {
        @Override
        public void onAnimationEnd(Animator animation) {
            if (mNodeMap.get(animation) == null) {
                throw new AndroidRuntimeException("Error: animation ended is not in the node map");
            }
            mNodeMap.get(animation).mEnded = true;

        }
    };

    public AnimatorSet() {
        super();
        mNodeMap.put(mDelayAnim, mRootNode);
        mNodes.add(mRootNode);
        boolean isPreO;
        // Set the flag to ignore calling end() without start() for pre-N releases
        Application app = ActivityThread.currentApplication();
        if (app == null || app.getApplicationInfo() == null) {
            mShouldIgnoreEndWithoutStart = true;
            isPreO = true;
        } else {
            if (app.getApplicationInfo().targetSdkVersion < Build.VERSION_CODES.N) {
                mShouldIgnoreEndWithoutStart = true;
            } else {
                mShouldIgnoreEndWithoutStart = false;
            }

            isPreO = app.getApplicationInfo().targetSdkVersion < Build.VERSION_CODES.O;
        }
        mShouldResetValuesAtStart = !isPreO;
        mEndCanBeCalled = !isPreO;
    }

    
Sets up this AnimatorSet to play all of the supplied animations at the same time. This is equivalent to calling play(Animator) with the first animator in the set and then Builder.with(Animator) with each of the other animators. Note that an Animator with a startDelay will not actually start until that delay elapses, which means that if the first animator in the list supplied to this constructor has a startDelay, none of the other animators will start until that first animator's startDelay has elapsed. 
Params:
items – The animations that will be started simultaneously./**
     * Sets up this AnimatorSet to play all of the supplied animations at the same time.
     * This is equivalent to calling {@link #play(Animator)} with the first animator in the
     * set and then {@link Builder#with(Animator)} with each of the other animators. Note that
     * an Animator with a {@link Animator#setStartDelay(long) startDelay} will not actually
     * start until that delay elapses, which means that if the first animator in the list
     * supplied to this constructor has a startDelay, none of the other animators will start
     * until that first animator's startDelay has elapsed.
     *
     * @param items The animations that will be started simultaneously.
     */
    public void playTogether(Animator... items) {
        if (items != null) {
            Builder builder = play(items[0]);
            for (int i = 1; i < items.length; ++i) {
                builder.with(items[i]);
            }
        }
    }

    
Sets up this AnimatorSet to play all of the supplied animations at the same time.
Params:
items – The animations that will be started simultaneously./**
     * Sets up this AnimatorSet to play all of the supplied animations at the same time.
     *
     * @param items The animations that will be started simultaneously.
     */
    public void playTogether(Collection<Animator> items) {
        if (items != null && items.size() > 0) {
            Builder builder = null;
            for (Animator anim : items) {
                if (builder == null) {
                    builder = play(anim);
                } else {
                    builder.with(anim);
                }
            }
        }
    }

    
Sets up this AnimatorSet to play each of the supplied animations when the
previous animation ends.
Params:
items – The animations that will be started one after another./**
     * Sets up this AnimatorSet to play each of the supplied animations when the
     * previous animation ends.
     *
     * @param items The animations that will be started one after another.
     */
    public void playSequentially(Animator... items) {
        if (items != null) {
            if (items.length == 1) {
                play(items[0]);
            } else {
                for (int i = 0; i < items.length - 1; ++i) {
                    play(items[i]).before(items[i + 1]);
                }
            }
        }
    }

    
Sets up this AnimatorSet to play each of the supplied animations when the
previous animation ends.
Params:
items – The animations that will be started one after another./**
     * Sets up this AnimatorSet to play each of the supplied animations when the
     * previous animation ends.
     *
     * @param items The animations that will be started one after another.
     */
    public void playSequentially(List<Animator> items) {
        if (items != null && items.size() > 0) {
            if (items.size() == 1) {
                play(items.get(0));
            } else {
                for (int i = 0; i < items.size() - 1; ++i) {
                    play(items.get(i)).before(items.get(i + 1));
                }
            }
        }
    }

    
Returns the current list of child Animator objects controlled by this
AnimatorSet. This is a copy of the internal list; modifications to the returned list
will not affect the AnimatorSet, although changes to the underlying Animator objects
will affect those objects being managed by the AnimatorSet.
Returns:
ArrayList The list of child animations of this AnimatorSet./**
     * Returns the current list of child Animator objects controlled by this
     * AnimatorSet. This is a copy of the internal list; modifications to the returned list
     * will not affect the AnimatorSet, although changes to the underlying Animator objects
     * will affect those objects being managed by the AnimatorSet.
     *
     * @return ArrayList<Animator> The list of child animations of this AnimatorSet.
     */
    public ArrayList<Animator> getChildAnimations() {
        ArrayList<Animator> childList = new ArrayList<Animator>();
        int size = mNodes.size();
        for (int i = 0; i < size; i++) {
            Node node = mNodes.get(i);
            if (node != mRootNode) {
                childList.add(node.mAnimation);
            }
        }
        return childList;
    }

    
Sets the target object for all current child animations of this AnimatorSet that take targets (ObjectAnimator and AnimatorSet). 
Params:
target – The object being animated/**
     * Sets the target object for all current {@link #getChildAnimations() child animations}
     * of this AnimatorSet that take targets ({@link ObjectAnimator} and
     * AnimatorSet).
     *
     * @param target The object being animated
     */
    @Override
    public void setTarget(Object target) {
        int size = mNodes.size();
        for (int i = 0; i < size; i++) {
            Node node = mNodes.get(i);
            Animator animation = node.mAnimation;
            if (animation instanceof AnimatorSet) {
                ((AnimatorSet)animation).setTarget(target);
            } else if (animation instanceof ObjectAnimator) {
                ((ObjectAnimator)animation).setTarget(target);
            }
        }
    }

    
@hide
/**
     * @hide
     */
    @Override
    public int getChangingConfigurations() {
        int conf = super.getChangingConfigurations();
        final int nodeCount = mNodes.size();
        for (int i = 0; i < nodeCount; i ++) {
            conf |= mNodes.get(i).mAnimation.getChangingConfigurations();
        }
        return conf;
    }

    
Sets the TimeInterpolator for all current child animations of this AnimatorSet. The default value is null, which means that no interpolator is set on this AnimatorSet. Setting the interpolator to any non-null value will cause that interpolator to be set on the child animations when the set is started. 
Params:
interpolator – the interpolator to be used by each child animation of this AnimatorSet/**
     * Sets the TimeInterpolator for all current {@link #getChildAnimations() child animations}
     * of this AnimatorSet. The default value is null, which means that no interpolator
     * is set on this AnimatorSet. Setting the interpolator to any non-null value
     * will cause that interpolator to be set on the child animations
     * when the set is started.
     *
     * @param interpolator the interpolator to be used by each child animation of this AnimatorSet
     */
    @Override
    public void setInterpolator(TimeInterpolator interpolator) {
        mInterpolator = interpolator;
    }

    @Override
    public TimeInterpolator getInterpolator() {
        return mInterpolator;
    }

    
This method creates a Builder object, which is used to
set up playing constraints. This initial play() method
tells the Builder the animation that is the dependency for
the succeeding commands to the Builder. For example,
calling play(a1).with(a2) sets up the AnimatorSet to play
a1 and a2 at the same time,
play(a1).before(a2) sets up the AnimatorSet to play
a1 first, followed by a2, and
play(a1).after(a2) sets up the AnimatorSet to play
a2 first, followed by a1.
Note that play() is the only way to tell the
Builder the animation upon which the dependency is created,
so successive calls to the various functions in Builder
will all refer to the initial parameter supplied in play()
as the dependency of the other animations. For example, calling
play(a1).before(a2).before(a3) will play both a2
and a3 when a1 ends; it does not set up a dependency between
a2 and a3.
Params:
anim – The animation that is the dependency used in later calls to the
methods in the returned Builder object. A null parameter will result
in a null Builder return value.
Returns:
Builder The object that constructs the AnimatorSet based on the dependencies
outlined in the calls to play and the other methods in the
Builder/**
     * This method creates a <code>Builder</code> object, which is used to
     * set up playing constraints. This initial <code>play()</code> method
     * tells the <code>Builder</code> the animation that is the dependency for
     * the succeeding commands to the <code>Builder</code>. For example,
     * calling <code>play(a1).with(a2)</code> sets up the AnimatorSet to play
     * <code>a1</code> and <code>a2</code> at the same time,
     * <code>play(a1).before(a2)</code> sets up the AnimatorSet to play
     * <code>a1</code> first, followed by <code>a2</code>, and
     * <code>play(a1).after(a2)</code> sets up the AnimatorSet to play
     * <code>a2</code> first, followed by <code>a1</code>.
     *
     * <p>Note that <code>play()</code> is the only way to tell the
     * <code>Builder</code> the animation upon which the dependency is created,
     * so successive calls to the various functions in <code>Builder</code>
     * will all refer to the initial parameter supplied in <code>play()</code>
     * as the dependency of the other animations. For example, calling
     * <code>play(a1).before(a2).before(a3)</code> will play both <code>a2</code>
     * and <code>a3</code> when a1 ends; it does not set up a dependency between
     * <code>a2</code> and <code>a3</code>.</p>
     *
     * @param anim The animation that is the dependency used in later calls to the
     * methods in the returned <code>Builder</code> object. A null parameter will result
     * in a null <code>Builder</code> return value.
     * @return Builder The object that constructs the AnimatorSet based on the dependencies
     * outlined in the calls to <code>play</code> and the other methods in the
     * <code>Builder</code object.
     */
    public Builder play(Animator anim) {
        if (anim != null) {
            return new Builder(anim);
        }
        return null;
    }

    
{@inheritDoc}
Note that canceling a AnimatorSet also cancels all of the animations that it
is responsible for.
/**
     * {@inheritDoc}
     *
     * <p>Note that canceling a <code>AnimatorSet</code> also cancels all of the animations that it
     * is responsible for.</p>
     */
    @SuppressWarnings("unchecked")
    @Override
    public void cancel() {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }
        if (isStarted()) {
            ArrayList<AnimatorListener> tmpListeners = null;
            if (mListeners != null) {
                tmpListeners = (ArrayList<AnimatorListener>) mListeners.clone();
                int size = tmpListeners.size();
                for (int i = 0; i < size; i++) {
                    tmpListeners.get(i).onAnimationCancel(this);
                }
            }
            ArrayList<Node> playingSet = new ArrayList<>(mPlayingSet);
            int setSize = playingSet.size();
            for (int i = 0; i < setSize; i++) {
                playingSet.get(i).mAnimation.cancel();
            }
            mPlayingSet.clear();
            endAnimation();
        }
    }

    // Force all the animations to end when the duration scale is 0.
    private void forceToEnd() {
        if (mEndCanBeCalled) {
            end();
            return;
        }

        // Note: we don't want to combine this case with the end() method below because in
        // the case of developer calling end(), we still need to make sure end() is explicitly
        // called on the child animators to maintain the old behavior.
        if (mReversing) {
            handleAnimationEvents(mLastEventId, 0, getTotalDuration());
        } else {
            long zeroScalePlayTime = getTotalDuration();
            if (zeroScalePlayTime == DURATION_INFINITE) {
                // Use a large number for the play time.
                zeroScalePlayTime = Integer.MAX_VALUE;
            }
            handleAnimationEvents(mLastEventId, mEvents.size() - 1, zeroScalePlayTime);
        }
        mPlayingSet.clear();
        endAnimation();
    }

    
{@inheritDoc}
Note that ending a AnimatorSet also ends all of the animations that it is
responsible for.
/**
     * {@inheritDoc}
     *
     * <p>Note that ending a <code>AnimatorSet</code> also ends all of the animations that it is
     * responsible for.</p>
     */
    @Override
    public void end() {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }
        if (mShouldIgnoreEndWithoutStart && !isStarted()) {
            return;
        }
        if (isStarted()) {
            // Iterate the animations that haven't finished or haven't started, and end them.
            if (mReversing) {
                // Between start() and first frame, mLastEventId would be unset (i.e. -1)
                mLastEventId = mLastEventId == -1 ? mEvents.size() : mLastEventId;
                while (mLastEventId > 0) {
                    mLastEventId = mLastEventId - 1;
                    AnimationEvent event = mEvents.get(mLastEventId);
                    Animator anim = event.mNode.mAnimation;
                    if (mNodeMap.get(anim).mEnded) {
                        continue;
                    }
                    if (event.mEvent == AnimationEvent.ANIMATION_END) {
                        anim.reverse();
                    } else if (event.mEvent == AnimationEvent.ANIMATION_DELAY_ENDED
                            && anim.isStarted()) {
                        // Make sure anim hasn't finished before calling end() so that we don't end
                        // already ended animations, which will cause start and end callbacks to be
                        // triggered again.
                        anim.end();
                    }
                }
            } else {
                while (mLastEventId < mEvents.size() - 1) {
                    // Avoid potential reentrant loop caused by child animators manipulating
                    // AnimatorSet's lifecycle (i.e. not a recommended approach).
                    mLastEventId = mLastEventId + 1;
                    AnimationEvent event = mEvents.get(mLastEventId);
                    Animator anim = event.mNode.mAnimation;
                    if (mNodeMap.get(anim).mEnded) {
                        continue;
                    }
                    if (event.mEvent == AnimationEvent.ANIMATION_START) {
                        anim.start();
                    } else if (event.mEvent == AnimationEvent.ANIMATION_END && anim.isStarted()) {
                        // Make sure anim hasn't finished before calling end() so that we don't end
                        // already ended animations, which will cause start and end callbacks to be
                        // triggered again.
                        anim.end();
                    }
                }
            }
            mPlayingSet.clear();
        }
        endAnimation();
    }

    
Returns true if any of the child animations of this AnimatorSet have been started and have not yet ended. Child animations will not be started until the AnimatorSet has gone past its initial delay set through setStartDelay(long). 
Returns:
Whether this AnimatorSet has gone past the initial delay, and at least one child
        animation has been started and not yet ended./**
     * Returns true if any of the child animations of this AnimatorSet have been started and have
     * not yet ended. Child animations will not be started until the AnimatorSet has gone past
     * its initial delay set through {@link #setStartDelay(long)}.
     *
     * @return Whether this AnimatorSet has gone past the initial delay, and at least one child
     *         animation has been started and not yet ended.
     */
    @Override
    public boolean isRunning() {
        if (mStartDelay == 0) {
            return mStarted;
        }
        return mLastFrameTime > 0;
    }

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

    
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;
        }
        long delta = startDelay - mStartDelay;
        if (delta == 0) {
            return;
        }
        mStartDelay = startDelay;
        if (!mDependencyDirty) {
            // Dependency graph already constructed, update all the nodes' start/end time
            int size = mNodes.size();
            for (int i = 0; i < size; i++) {
                Node node = mNodes.get(i);
                if (node == mRootNode) {
                    node.mEndTime = mStartDelay;
                } else {
                    node.mStartTime = node.mStartTime == DURATION_INFINITE ?
                            DURATION_INFINITE : node.mStartTime + delta;
                    node.mEndTime = node.mEndTime == DURATION_INFINITE ?
                            DURATION_INFINITE : node.mEndTime + delta;
                }
            }
            // Update total duration, if necessary.
            if (mTotalDuration != DURATION_INFINITE) {
                mTotalDuration += delta;
            }
        }
    }

    
Gets the length of each of the child animations of this AnimatorSet. This value may
be less than 0, which indicates that no duration has been set on this AnimatorSet
and each of the child animations will use their own duration.
Returns:
The length of the animation, in milliseconds, of each of the child
animations of this AnimatorSet./**
     * Gets the length of each of the child animations of this AnimatorSet. This value may
     * be less than 0, which indicates that no duration has been set on this AnimatorSet
     * and each of the child animations will use their own duration.
     *
     * @return The length of the animation, in milliseconds, of each of the child
     * animations of this AnimatorSet.
     */
    @Override
    public long getDuration() {
        return mDuration;
    }

    
Sets the length of each of the current child animations of this AnimatorSet. By default,
each child animation will use its own duration. If the duration is set on the AnimatorSet,
then each child animation inherits this duration.
Params:
duration – The length of the animation, in milliseconds, of each of the child
animations of this AnimatorSet./**
     * Sets the length of each of the current child animations of this AnimatorSet. By default,
     * each child animation will use its own duration. If the duration is set on the AnimatorSet,
     * then each child animation inherits this duration.
     *
     * @param duration The length of the animation, in milliseconds, of each of the child
     * animations of this AnimatorSet.
     */
    @Override
    public AnimatorSet setDuration(long duration) {
        if (duration < 0) {
            throw new IllegalArgumentException("duration must be a value of zero or greater");
        }
        mDependencyDirty = true;
        // Just record the value for now - it will be used later when the AnimatorSet starts
        mDuration = duration;
        return this;
    }

    @Override
    public void setupStartValues() {
        int size = mNodes.size();
        for (int i = 0; i < size; i++) {
            Node node = mNodes.get(i);
            if (node != mRootNode) {
                node.mAnimation.setupStartValues();
            }
        }
    }

    @Override
    public void setupEndValues() {
        int size = mNodes.size();
        for (int i = 0; i < size; i++) {
            Node node = mNodes.get(i);
            if (node != mRootNode) {
                node.mAnimation.setupEndValues();
            }
        }
    }

    @Override
    public void pause() {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }
        boolean previouslyPaused = mPaused;
        super.pause();
        if (!previouslyPaused && mPaused) {
            mPauseTime = -1;
        }
    }

    @Override
    public void resume() {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }
        boolean previouslyPaused = mPaused;
        super.resume();
        if (previouslyPaused && !mPaused) {
            if (mPauseTime >= 0) {
                addAnimationCallback(0);
            }
        }
    }

    
{@inheritDoc}
Starting this AnimatorSet will, in turn, start the animations for which
it is responsible. The details of when exactly those animations are started depends on
the dependency relationships that have been set up between the animations.
Note: Manipulating AnimatorSet's lifecycle in the child animators' listener callbacks will lead to undefined behaviors. Also, AnimatorSet will ignore any seeking in the child animators once start() is called. /**
     * {@inheritDoc}
     *
     * <p>Starting this <code>AnimatorSet</code> will, in turn, start the animations for which
     * it is responsible. The details of when exactly those animations are started depends on
     * the dependency relationships that have been set up between the animations.
     *
     * <b>Note:</b> Manipulating AnimatorSet's lifecycle in the child animators' listener callbacks
     * will lead to undefined behaviors. Also, AnimatorSet will ignore any seeking in the child
     * animators once {@link #start()} is called.
     */
    @SuppressWarnings("unchecked")
    @Override
    public void start() {
        start(false, true);
    }

    @Override
    void startWithoutPulsing(boolean inReverse) {
        start(inReverse, false);
    }

    private void initAnimation() {
        if (mInterpolator != null) {
            for (int i = 0; i < mNodes.size(); i++) {
                Node node = mNodes.get(i);
                node.mAnimation.setInterpolator(mInterpolator);
            }
        }
        updateAnimatorsDuration();
        createDependencyGraph();
    }

    private void start(boolean inReverse, boolean selfPulse) {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }
        mStarted = true;
        mSelfPulse = selfPulse;
        mPaused = false;
        mPauseTime = -1;

        int size = mNodes.size();
        for (int i = 0; i < size; i++) {
            Node node = mNodes.get(i);
            node.mEnded = false;
            node.mAnimation.setAllowRunningAsynchronously(false);
        }

        initAnimation();
        if (inReverse && !canReverse()) {
            throw new UnsupportedOperationException("Cannot reverse infinite AnimatorSet");
        }

        mReversing = inReverse;

        // Now that all dependencies are set up, start the animations that should be started.
        boolean isEmptySet = isEmptySet(this);
        if (!isEmptySet) {
            startAnimation();
        }

        if (mListeners != null) {
            ArrayList<AnimatorListener> tmpListeners =
                    (ArrayList<AnimatorListener>) mListeners.clone();
            int numListeners = tmpListeners.size();
            for (int i = 0; i < numListeners; ++i) {
                tmpListeners.get(i).onAnimationStart(this, inReverse);
            }
        }
        if (isEmptySet) {
            // In the case of empty AnimatorSet, or 0 duration scale, we will trigger the
            // onAnimationEnd() right away.
            end();
        }
    }

    // Returns true if set is empty or contains nothing but animator sets with no start delay.
    private static boolean isEmptySet(AnimatorSet set) {
        if (set.getStartDelay() > 0) {
            return false;
        }
        for (int i = 0; i < set.getChildAnimations().size(); i++) {
            Animator anim = set.getChildAnimations().get(i);
            if (!(anim instanceof AnimatorSet)) {
                // Contains non-AnimatorSet, not empty.
                return false;
            } else {
                if (!isEmptySet((AnimatorSet) anim)) {
                    return false;
                }
            }
        }
        return true;
    }

    private void updateAnimatorsDuration() {
        if (mDuration >= 0) {
            // If the duration was set on this AnimatorSet, pass it along to all child animations
            int size = mNodes.size();
            for (int i = 0; i < size; i++) {
                Node node = mNodes.get(i);
                // TODO: don't set the duration of the timing-only nodes created by AnimatorSet to
                // insert "play-after" delays
                node.mAnimation.setDuration(mDuration);
            }
        }
        mDelayAnim.setDuration(mStartDelay);
    }

    @Override
    void skipToEndValue(boolean inReverse) {
        if (!isInitialized()) {
            throw new UnsupportedOperationException("Children must be initialized.");
        }

        // This makes sure the animation events are sorted an up to date.
        initAnimation();

        // Calling skip to the end in the sequence that they would be called in a forward/reverse
        // run, such that the sequential animations modifying the same property would have
        // the right value in the end.
        if (inReverse) {
            for (int i = mEvents.size() - 1; i >= 0; i--) {
                if (mEvents.get(i).mEvent == AnimationEvent.ANIMATION_DELAY_ENDED) {
                    mEvents.get(i).mNode.mAnimation.skipToEndValue(true);
                }
            }
        } else {
            for (int i = 0; i < mEvents.size(); i++) {
                if (mEvents.get(i).mEvent == AnimationEvent.ANIMATION_END) {
                    mEvents.get(i).mNode.mAnimation.skipToEndValue(false);
                }
            }
        }
    }

    
Internal only. This method sets the animation values based on the play time. It also fast forward or backward all the child animations progress accordingly. This method is also responsible for calling AnimationListener.onAnimationRepeat(Animation), as needed, based on the last play time and current play time. /**
     * Internal only.
     *
     * This method sets the animation values based on the play time. It also fast forward or
     * backward all the child animations progress accordingly.
     *
     * This method is also responsible for calling
     * {@link android.view.animation.Animation.AnimationListener#onAnimationRepeat(Animation)},
     * as needed, based on the last play time and current play time.
     */
    @Override
    void animateBasedOnPlayTime(long currentPlayTime, long lastPlayTime, boolean inReverse) {
        if (currentPlayTime < 0 || lastPlayTime < 0) {
            throw new UnsupportedOperationException("Error: Play time should never be negative.");
        }
        // TODO: take into account repeat counts and repeat callback when repeat is implemented.
        // Clamp currentPlayTime and lastPlayTime

        // TODO: Make this more efficient

        // Convert the play times to the forward direction.
        if (inReverse) {
            if (getTotalDuration() == DURATION_INFINITE) {
                throw new UnsupportedOperationException("Cannot reverse AnimatorSet with infinite"
                        + " duration");
            }
            long duration = getTotalDuration() - mStartDelay;
            currentPlayTime = Math.min(currentPlayTime, duration);
            currentPlayTime = duration - currentPlayTime;
            lastPlayTime = duration - lastPlayTime;
            inReverse = false;
        }
        // Skip all values to start, and iterate mEvents to get animations to the right fraction.
        skipToStartValue(false);

        ArrayList<Node> unfinishedNodes = new ArrayList<>();
        // Assumes forward playing from here on.
        for (int i = 0; i < mEvents.size(); i++) {
            AnimationEvent event = mEvents.get(i);
            if (event.getTime() > currentPlayTime || event.getTime() == DURATION_INFINITE) {
                break;
            }

            // This animation started prior to the current play time, and won't finish before the
            // play time, add to the unfinished list.
            if (event.mEvent == AnimationEvent.ANIMATION_DELAY_ENDED) {
                if (event.mNode.mEndTime == DURATION_INFINITE
                        || event.mNode.mEndTime > currentPlayTime) {
                    unfinishedNodes.add(event.mNode);
                }
            }
            // For animations that do finish before the play time, end them in the sequence that
            // they would in a normal run.
            if (event.mEvent == AnimationEvent.ANIMATION_END) {
                // Skip to the end of the animation.
                event.mNode.mAnimation.skipToEndValue(false);
            }
        }

        // Seek unfinished animation to the right time.
        for (int i = 0; i < unfinishedNodes.size(); i++) {
            Node node = unfinishedNodes.get(i);
            long playTime = getPlayTimeForNode(currentPlayTime, node, inReverse);
            if (!inReverse) {
                playTime -= node.mAnimation.getStartDelay();
            }
            node.mAnimation.animateBasedOnPlayTime(playTime, lastPlayTime, inReverse);
        }
    }

    @Override
    boolean isInitialized() {
        if (mChildrenInitialized) {
            return true;
        }

        boolean allInitialized = true;
        for (int i = 0; i < mNodes.size(); i++) {
            if (!mNodes.get(i).mAnimation.isInitialized()) {
                allInitialized = false;
                break;
            }
        }
        mChildrenInitialized = allInitialized;
        return mChildrenInitialized;
    }

    private void skipToStartValue(boolean inReverse) {
        skipToEndValue(!inReverse);
    }

    
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.
                Unless the animation is reversing, the playtime is considered the time since
                the end of the start delay of the AnimatorSet in a forward playing direction./**
     * 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.
     *                 Unless the animation is reversing, the playtime is considered the time since
     *                 the end of the start delay of the AnimatorSet in a forward playing direction.
     *
     */
    public void setCurrentPlayTime(long playTime) {
        if (mReversing && getTotalDuration() == DURATION_INFINITE) {
            // Should never get here
            throw new UnsupportedOperationException("Error: Cannot seek in reverse in an infinite"
                    + " AnimatorSet");
        }

        if ((getTotalDuration() != DURATION_INFINITE && playTime > getTotalDuration() - mStartDelay)
                || playTime < 0) {
            throw new UnsupportedOperationException("Error: Play time should always be in between"
                    + "0 and duration.");
        }

        initAnimation();

        if (!isStarted()) {
            if (mReversing) {
                throw new UnsupportedOperationException("Error: Something went wrong. mReversing"
                        + " should not be set when AnimatorSet is not started.");
            }
            if (!mSeekState.isActive()) {
                findLatestEventIdForTime(0);
                // Set all the values to start values.
                initChildren();
                skipToStartValue(mReversing);
                mSeekState.setPlayTime(0, mReversing);
            }
            animateBasedOnPlayTime(playTime, 0, mReversing);
            mSeekState.setPlayTime(playTime, mReversing);
        } else {
            // If the animation is running, just set the seek time and wait until the next frame
            // (i.e. doAnimationFrame(...)) to advance the animation.
            mSeekState.setPlayTime(playTime, mReversing);
        }
    }

    
Returns the milliseconds elapsed since the start of the animation.
For ongoing animations, this method returns the current progress of the animation in terms of play time. For an animation that has not yet been started: if the animation has been seeked to a certain time via setCurrentPlayTime(long), the seeked play time will be returned; otherwise, this method will return 0. 
Returns:
the current position in time of the animation in milliseconds/**
     * Returns the milliseconds elapsed since the start of the animation.
     *
     * <p>For ongoing animations, this method returns the current progress of the animation in
     * terms of play time. For an animation that has not yet been started: if the animation has been
     * seeked to a certain time via {@link #setCurrentPlayTime(long)}, the seeked play time will
     * be returned; otherwise, this method will return 0.
     *
     * @return the current position in time of the animation in milliseconds
     */
    public long getCurrentPlayTime() {
        if (mSeekState.isActive()) {
            return mSeekState.getPlayTime();
        }
        if (mLastFrameTime == -1) {
            // Not yet started or during start delay
            return 0;
        }
        float durationScale = ValueAnimator.getDurationScale();
        durationScale = durationScale == 0 ? 1 : durationScale;
        if (mReversing) {
            return (long) ((mLastFrameTime - mFirstFrame) / durationScale);
        } else {
            return (long) ((mLastFrameTime - mFirstFrame - mStartDelay) / durationScale);
        }
    }

    private void initChildren() {
        if (!isInitialized()) {
            mChildrenInitialized = true;
            // Forcefully initialize all children based on their end time, so that if the start
            // value of a child is dependent on a previous animation, the animation will be
            // initialized after the the previous animations have been advanced to the end.
            skipToEndValue(false);
        }
    }

    
Params:
frameTime – The frame start time, in the uptimeMillis.uptimeMillis() time base.
Returns:
@hide
/**
     * @param frameTime The frame start time, in the {@link SystemClock#uptimeMillis()} time
     *                  base.
     * @return
     * @hide
     */
    @Override
    public boolean doAnimationFrame(long frameTime) {
        float durationScale = ValueAnimator.getDurationScale();
        if (durationScale == 0f) {
            // Duration scale is 0, end the animation right away.
            forceToEnd();
            return true;
        }

        // After the first frame comes in, we need to wait for start delay to pass before updating
        // any animation values.
        if (mFirstFrame < 0) {
            mFirstFrame = frameTime;
        }

        // Handle pause/resume
        if (mPaused) {
            // Note: Child animations don't receive pause events. Since it's never a contract that
            // the child animators will be paused when set is paused, this is unlikely to be an
            // issue.
            mPauseTime = frameTime;
            removeAnimationCallback();
            return false;
        } else if (mPauseTime > 0) {
                // Offset by the duration that the animation was paused
            mFirstFrame += (frameTime - mPauseTime);
            mPauseTime = -1;
        }

        // Continue at seeked position
        if (mSeekState.isActive()) {
            mSeekState.updateSeekDirection(mReversing);
            if (mReversing) {
                mFirstFrame = (long) (frameTime - mSeekState.getPlayTime() * durationScale);
            } else {
                mFirstFrame = (long) (frameTime - (mSeekState.getPlayTime() + mStartDelay)
                        * durationScale);
            }
            mSeekState.reset();
        }

        if (!mReversing && frameTime < mFirstFrame + mStartDelay * durationScale) {
            // Still during start delay in a forward playing case.
            return false;
        }

        // From here on, we always use unscaled play time. Note this unscaled playtime includes
        // the start delay.
        long unscaledPlayTime = (long) ((frameTime - mFirstFrame) / durationScale);
        mLastFrameTime = frameTime;

        // 1. Pulse the animators that will start or end in this frame
        // 2. Pulse the animators that will finish in a later frame
        int latestId = findLatestEventIdForTime(unscaledPlayTime);
        int startId = mLastEventId;

        handleAnimationEvents(startId, latestId, unscaledPlayTime);

        mLastEventId = latestId;

        // Pump a frame to the on-going animators
        for (int i = 0; i < mPlayingSet.size(); i++) {
            Node node = mPlayingSet.get(i);
            if (!node.mEnded) {
                pulseFrame(node, getPlayTimeForNode(unscaledPlayTime, node));
            }
        }

        // Remove all the finished anims
        for (int i = mPlayingSet.size() - 1; i >= 0; i--) {
            if (mPlayingSet.get(i).mEnded) {
                mPlayingSet.remove(i);
            }
        }

        boolean finished = false;
        if (mReversing) {
            if (mPlayingSet.size() == 1 && mPlayingSet.get(0) == mRootNode) {
                // The only animation that is running is the delay animation.
                finished = true;
            } else if (mPlayingSet.isEmpty() && mLastEventId < 3) {
                // The only remaining animation is the delay animation
                finished = true;
            }
        } else {
            finished = mPlayingSet.isEmpty() && mLastEventId == mEvents.size() - 1;
        }

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

    
@hide
/**
     * @hide
     */
    @Override
    public void commitAnimationFrame(long frameTime) {
        // No op.
    }

    @Override
    boolean pulseAnimationFrame(long frameTime) {
        return doAnimationFrame(frameTime);
    }

    
When playing forward, we call start() at the animation's scheduled start time, and make sure
to pump a frame at the animation's scheduled end time.
When playing in reverse, we should reverse the animation when we hit animation's end event,
and expect the animation to end at the its delay ended event, rather than start event.
/**
     * When playing forward, we call start() at the animation's scheduled start time, and make sure
     * to pump a frame at the animation's scheduled end time.
     *
     * When playing in reverse, we should reverse the animation when we hit animation's end event,
     * and expect the animation to end at the its delay ended event, rather than start event.
     */
    private void handleAnimationEvents(int startId, int latestId, long playTime) {
        if (mReversing) {
            startId = startId == -1 ? mEvents.size() : startId;
            for (int i = startId - 1; i >= latestId; i--) {
                AnimationEvent event = mEvents.get(i);
                Node node = event.mNode;
                if (event.mEvent == AnimationEvent.ANIMATION_END) {
                    if (node.mAnimation.isStarted()) {
                        // If the animation has already been started before its due time (i.e.
                        // the child animator is being manipulated outside of the AnimatorSet), we
                        // need to cancel the animation to reset the internal state (e.g. frame
                        // time tracking) and remove the self pulsing callbacks
                        node.mAnimation.cancel();
                    }
                    node.mEnded = false;
                    mPlayingSet.add(event.mNode);
                    node.mAnimation.startWithoutPulsing(true);
                    pulseFrame(node, 0);
                } else if (event.mEvent == AnimationEvent.ANIMATION_DELAY_ENDED && !node.mEnded) {
                    // end event:
                    pulseFrame(node, getPlayTimeForNode(playTime, node));
                }
            }
        } else {
            for (int i = startId + 1; i <= latestId; i++) {
                AnimationEvent event = mEvents.get(i);
                Node node = event.mNode;
                if (event.mEvent == AnimationEvent.ANIMATION_START) {
                    mPlayingSet.add(event.mNode);
                    if (node.mAnimation.isStarted()) {
                        // If the animation has already been started before its due time (i.e.
                        // the child animator is being manipulated outside of the AnimatorSet), we
                        // need to cancel the animation to reset the internal state (e.g. frame
                        // time tracking) and remove the self pulsing callbacks
                        node.mAnimation.cancel();
                    }
                    node.mEnded = false;
                    node.mAnimation.startWithoutPulsing(false);
                    pulseFrame(node, 0);
                } else if (event.mEvent == AnimationEvent.ANIMATION_END && !node.mEnded) {
                    // start event:
                    pulseFrame(node, getPlayTimeForNode(playTime, node));
                }
            }
        }
    }

    
This method pulses frames into child animations. It scales the input animation play time
with the duration scale and pass that to the child animation via pulseAnimationFrame(long).
Params:
node – child animator node
animPlayTime – unscaled play time (including start delay) for the child animator/**
     * This method pulses frames into child animations. It scales the input animation play time
     * with the duration scale and pass that to the child animation via pulseAnimationFrame(long).
     *
     * @param node child animator node
     * @param animPlayTime unscaled play time (including start delay) for the child animator
     */
    private void pulseFrame(Node node, long animPlayTime) {
        if (!node.mEnded) {
            float durationScale = ValueAnimator.getDurationScale();
            durationScale = durationScale == 0  ? 1 : durationScale;
            node.mEnded = node.mAnimation.pulseAnimationFrame(
                    (long) (animPlayTime * durationScale));
        }
    }

    private long getPlayTimeForNode(long overallPlayTime, Node node) {
        return getPlayTimeForNode(overallPlayTime, node, mReversing);
    }

    private long getPlayTimeForNode(long overallPlayTime, Node node, boolean inReverse) {
        if (inReverse) {
            overallPlayTime = getTotalDuration() - overallPlayTime;
            return node.mEndTime - overallPlayTime;
        } else {
            return overallPlayTime - node.mStartTime;
        }
    }

    private void startAnimation() {
        addDummyListener();

        // Register animation callback
        addAnimationCallback(0);

        if (mSeekState.getPlayTimeNormalized() == 0 && mReversing) {
            // Maintain old behavior, if seeked to 0 then call reverse, we'll treat the case
            // the same as no seeking at all.
            mSeekState.reset();
        }
        // Set the child animators to the right end:
        if (mShouldResetValuesAtStart) {
            if (isInitialized()) {
                skipToEndValue(!mReversing);
            } else if (mReversing) {
                // Reversing but haven't initialized all the children yet.
                initChildren();
                skipToEndValue(!mReversing);
            } else {
                // If not all children are initialized and play direction is forward
                for (int i = mEvents.size() - 1; i >= 0; i--) {
                    if (mEvents.get(i).mEvent == AnimationEvent.ANIMATION_DELAY_ENDED) {
                        Animator anim = mEvents.get(i).mNode.mAnimation;
                        // Only reset the animations that have been initialized to start value,
                        // so that if they are defined without a start value, they will get the
                        // values set at the right time (i.e. the next animation run)
                        if (anim.isInitialized()) {
                            anim.skipToEndValue(true);
                        }
                    }
                }
            }
        }

        if (mReversing || mStartDelay == 0 || mSeekState.isActive()) {
            long playTime;
            // If no delay, we need to call start on the first animations to be consistent with old
            // behavior.
            if (mSeekState.isActive()) {
                mSeekState.updateSeekDirection(mReversing);
                playTime = mSeekState.getPlayTime();
            } else {
                playTime = 0;
            }
            int toId = findLatestEventIdForTime(playTime);
            handleAnimationEvents(-1, toId, playTime);
            for (int i = mPlayingSet.size() - 1; i >= 0; i--) {
                if (mPlayingSet.get(i).mEnded) {
                    mPlayingSet.remove(i);
                }
            }
            mLastEventId = toId;
        }
    }

    // This is to work around the issue in b/34736819, as the old behavior in AnimatorSet had
    // masked a real bug in play movies. TODO: remove this and below once the root cause is fixed.
    private void addDummyListener() {
        for (int i = 1; i < mNodes.size(); i++) {
            mNodes.get(i).mAnimation.addListener(mDummyListener);
        }
    }

    private void removeDummyListener() {
        for (int i = 1; i < mNodes.size(); i++) {
            mNodes.get(i).mAnimation.removeListener(mDummyListener);
        }
    }

    private int findLatestEventIdForTime(long currentPlayTime) {
        int size = mEvents.size();
        int latestId = mLastEventId;
        // Call start on the first animations now to be consistent with the old behavior
        if (mReversing) {
            currentPlayTime = getTotalDuration() - currentPlayTime;
            mLastEventId = mLastEventId == -1 ? size : mLastEventId;
            for (int j = mLastEventId - 1; j >= 0; j--) {
                AnimationEvent event = mEvents.get(j);
                if (event.getTime() >= currentPlayTime) {
                    latestId = j;
                }
            }
        } else {
            for (int i = mLastEventId + 1; i < size; i++) {
                AnimationEvent event = mEvents.get(i);
                // TODO: need a function that accounts for infinite duration to compare time
                if (event.getTime() != DURATION_INFINITE && event.getTime() <= currentPlayTime) {
                    latestId = i;
                }
            }
        }
        return latestId;
    }

    private void endAnimation() {
        mStarted = false;
        mLastFrameTime = -1;
        mFirstFrame = -1;
        mLastEventId = -1;
        mPaused = false;
        mPauseTime = -1;
        mSeekState.reset();
        mPlayingSet.clear();

        // No longer receive callbacks
        removeAnimationCallback();
        // Call end listener
        if (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);
            }
        }
        removeDummyListener();
        mSelfPulse = true;
        mReversing = false;
    }

    private void removeAnimationCallback() {
        if (!mSelfPulse) {
            return;
        }
        AnimationHandler handler = AnimationHandler.getInstance();
        handler.removeCallback(this);
    }

    private void addAnimationCallback(long delay) {
        if (!mSelfPulse) {
            return;
        }
        AnimationHandler handler = AnimationHandler.getInstance();
        handler.addAnimationFrameCallback(this, delay);
    }

    @Override
    public AnimatorSet clone() {
        final AnimatorSet anim = (AnimatorSet) super.clone();
        /*
         * The basic clone() operation copies all items. This doesn't work very well for
         * AnimatorSet, because it will copy references that need to be recreated and state
         * that may not apply. What we need to do now is put the clone in an uninitialized
         * state, with fresh, empty data structures. Then we will build up the nodes list
         * manually, as we clone each Node (and its animation). The clone will then be sorted,
         * and will populate any appropriate lists, when it is started.
         */
        final int nodeCount = mNodes.size();
        anim.mStarted = false;
        anim.mLastFrameTime = -1;
        anim.mFirstFrame = -1;
        anim.mLastEventId = -1;
        anim.mPaused = false;
        anim.mPauseTime = -1;
        anim.mSeekState = new SeekState();
        anim.mSelfPulse = true;
        anim.mPlayingSet = new ArrayList<Node>();
        anim.mNodeMap = new ArrayMap<Animator, Node>();
        anim.mNodes = new ArrayList<Node>(nodeCount);
        anim.mEvents = new ArrayList<AnimationEvent>();
        anim.mDummyListener = new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                if (anim.mNodeMap.get(animation) == null) {
                    throw new AndroidRuntimeException("Error: animation ended is not in the node"
                            + " map");
                }
                anim.mNodeMap.get(animation).mEnded = true;

            }
        };
        anim.mReversing = false;
        anim.mDependencyDirty = true;

        // Walk through the old nodes list, cloning each node and adding it to the new nodemap.
        // One problem is that the old node dependencies point to nodes in the old AnimatorSet.
        // We need to track the old/new nodes in order to reconstruct the dependencies in the clone.

        HashMap<Node, Node> clonesMap = new HashMap<>(nodeCount);
        for (int n = 0; n < nodeCount; n++) {
            final Node node = mNodes.get(n);
            Node nodeClone = node.clone();
            // Remove the old internal listener from the cloned child
            nodeClone.mAnimation.removeListener(mDummyListener);
            clonesMap.put(node, nodeClone);
            anim.mNodes.add(nodeClone);
            anim.mNodeMap.put(nodeClone.mAnimation, nodeClone);
        }

        anim.mRootNode = clonesMap.get(mRootNode);
        anim.mDelayAnim = (ValueAnimator) anim.mRootNode.mAnimation;

        // Now that we've cloned all of the nodes, we're ready to walk through their
        // dependencies, mapping the old dependencies to the new nodes
        for (int i = 0; i < nodeCount; i++) {
            Node node = mNodes.get(i);
            // Update dependencies for node's clone
            Node nodeClone = clonesMap.get(node);
            nodeClone.mLatestParent = node.mLatestParent == null
                    ? null : clonesMap.get(node.mLatestParent);
            int size = node.mChildNodes == null ? 0 : node.mChildNodes.size();
            for (int j = 0; j < size; j++) {
                nodeClone.mChildNodes.set(j, clonesMap.get(node.mChildNodes.get(j)));
            }
            size = node.mSiblings == null ? 0 : node.mSiblings.size();
            for (int j = 0; j < size; j++) {
                nodeClone.mSiblings.set(j, clonesMap.get(node.mSiblings.get(j)));
            }
            size = node.mParents == null ? 0 : node.mParents.size();
            for (int j = 0; j < size; j++) {
                nodeClone.mParents.set(j, clonesMap.get(node.mParents.get(j)));
            }
        }
        return anim;
    }


    
AnimatorSet is only reversible when the set contains no sequential animation, and no child
animators have a start delay.
@hide
/**
     * AnimatorSet is only reversible when the set contains no sequential animation, and no child
     * animators have a start delay.
     * @hide
     */
    @Override
    public boolean canReverse() {
        return getTotalDuration() != DURATION_INFINITE;
    }

    
Plays the AnimatorSet in reverse. If the animation has been seeked to a specific play time using setCurrentPlayTime(long), it will play backwards from the point seeked when reverse was called. Otherwise, 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. 

Note: reverse is not supported for infinite AnimatorSet.
/**
     * Plays the AnimatorSet in reverse. If the animation has been seeked to a specific play time
     * using {@link #setCurrentPlayTime(long)}, it will play backwards from the point seeked when
     * reverse was called. Otherwise, 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.
     * <p>
     * Note: reverse is not supported for infinite AnimatorSet.
     */
    @Override
    public void reverse() {
        start(true, true);
    }

    @Override
    public String toString() {
        String returnVal = "AnimatorSet@" + Integer.toHexString(hashCode()) + "{";
        int size = mNodes.size();
        for (int i = 0; i < size; i++) {
            Node node = mNodes.get(i);
            returnVal += "\n    " + node.mAnimation.toString();
        }
        return returnVal + "\n}";
    }

    private void printChildCount() {
        // Print out the child count through a level traverse.
        ArrayList<Node> list = new ArrayList<>(mNodes.size());
        list.add(mRootNode);
        Log.d(TAG, "Current tree: ");
        int index = 0;
        while (index < list.size()) {
            int listSize = list.size();
            StringBuilder builder = new StringBuilder();
            for (; index < listSize; index++) {
                Node node = list.get(index);
                int num = 0;
                if (node.mChildNodes != null) {
                    for (int i = 0; i < node.mChildNodes.size(); i++) {
                        Node child = node.mChildNodes.get(i);
                        if (child.mLatestParent == node) {
                            num++;
                            list.add(child);
                        }
                    }
                }
                builder.append(" ");
                builder.append(num);
            }
            Log.d(TAG, builder.toString());
        }
    }

    private void createDependencyGraph() {
        if (!mDependencyDirty) {
            // Check whether any duration of the child animations has changed
            boolean durationChanged = false;
            for (int i = 0; i < mNodes.size(); i++) {
                Animator anim = mNodes.get(i).mAnimation;
                if (mNodes.get(i).mTotalDuration != anim.getTotalDuration()) {
                    durationChanged = true;
                    break;
                }
            }
            if (!durationChanged) {
                return;
            }
        }

        mDependencyDirty = false;
        // Traverse all the siblings and make sure they have all the parents
        int size = mNodes.size();
        for (int i = 0; i < size; i++) {
            mNodes.get(i).mParentsAdded = false;
        }
        for (int i = 0; i < size; i++) {
            Node node = mNodes.get(i);
            if (node.mParentsAdded) {
                continue;
            }

            node.mParentsAdded = true;
            if (node.mSiblings == null) {
                continue;
            }

            // Find all the siblings
            findSiblings(node, node.mSiblings);
            node.mSiblings.remove(node);

            // Get parents from all siblings
            int siblingSize = node.mSiblings.size();
            for (int j = 0; j < siblingSize; j++) {
                node.addParents(node.mSiblings.get(j).mParents);
            }

            // Now make sure all siblings share the same set of parents
            for (int j = 0; j < siblingSize; j++) {
                Node sibling = node.mSiblings.get(j);
                sibling.addParents(node.mParents);
                sibling.mParentsAdded = true;
            }
        }

        for (int i = 0; i < size; i++) {
            Node node = mNodes.get(i);
            if (node != mRootNode && node.mParents == null) {
                node.addParent(mRootNode);
            }
        }

        // Do a DFS on the tree
        ArrayList<Node> visited = new ArrayList<Node>(mNodes.size());
        // Assign start/end time
        mRootNode.mStartTime = 0;
        mRootNode.mEndTime = mDelayAnim.getDuration();
        updatePlayTime(mRootNode, visited);

        sortAnimationEvents();
        mTotalDuration = mEvents.get(mEvents.size() - 1).getTime();
    }

    private void sortAnimationEvents() {
        // Sort the list of events in ascending order of their time
        // Create the list including the delay animation.
        mEvents.clear();
        for (int i = 1; i < mNodes.size(); i++) {
            Node node = mNodes.get(i);
            mEvents.add(new AnimationEvent(node, AnimationEvent.ANIMATION_START));
            mEvents.add(new AnimationEvent(node, AnimationEvent.ANIMATION_DELAY_ENDED));
            mEvents.add(new AnimationEvent(node, AnimationEvent.ANIMATION_END));
        }
        mEvents.sort(new Comparator<AnimationEvent>() {
            @Override
            public int compare(AnimationEvent e1, AnimationEvent e2) {
                long t1 = e1.getTime();
                long t2 = e2.getTime();
                if (t1 == t2) {
                    // For events that happen at the same time, we need them to be in the sequence
                    // (end, start, start delay ended)
                    if (e2.mEvent + e1.mEvent == AnimationEvent.ANIMATION_START
                            + AnimationEvent.ANIMATION_DELAY_ENDED) {
                        // Ensure start delay happens after start
                        return e1.mEvent - e2.mEvent;
                    } else {
                        return e2.mEvent - e1.mEvent;
                    }
                }
                if (t2 == DURATION_INFINITE) {
                    return -1;
                }
                if (t1 == DURATION_INFINITE) {
                    return 1;
                }
                // When neither event happens at INFINITE time:
                return (int) (t1 - t2);
            }
        });

        int eventSize = mEvents.size();
        // For the same animation, start event has to happen before end.
        for (int i = 0; i < eventSize;) {
            AnimationEvent event = mEvents.get(i);
            if (event.mEvent == AnimationEvent.ANIMATION_END) {
                boolean needToSwapStart;
                if (event.mNode.mStartTime == event.mNode.mEndTime) {
                    needToSwapStart = true;
                } else if (event.mNode.mEndTime == event.mNode.mStartTime
                        + event.mNode.mAnimation.getStartDelay()) {
                    // Swapping start delay
                    needToSwapStart = false;
                } else {
                    i++;
                    continue;
                }

                int startEventId = eventSize;
                int startDelayEndId = eventSize;
                for (int j = i + 1; j < eventSize; j++) {
                    if (startEventId < eventSize && startDelayEndId < eventSize) {
                        break;
                    }
                    if (mEvents.get(j).mNode == event.mNode) {
                        if (mEvents.get(j).mEvent == AnimationEvent.ANIMATION_START) {
                            // Found start event
                            startEventId = j;
                        } else if (mEvents.get(j).mEvent == AnimationEvent.ANIMATION_DELAY_ENDED) {
                            startDelayEndId = j;
                        }
                    }

                }
                if (needToSwapStart && startEventId == mEvents.size()) {
                    throw new UnsupportedOperationException("Something went wrong, no start is"
                            + "found after stop for an animation that has the same start and end"
                            + "time.");

                }
                if (startDelayEndId == mEvents.size()) {
                    throw new UnsupportedOperationException("Something went wrong, no start"
                            + "delay end is found after stop for an animation");

                }

                // We need to make sure start is inserted before start delay ended event,
                // because otherwise inserting start delay ended events first would change
                // the start event index.
                if (needToSwapStart) {
                    AnimationEvent startEvent = mEvents.remove(startEventId);
                    mEvents.add(i, startEvent);
                    i++;
                }

                AnimationEvent startDelayEndEvent = mEvents.remove(startDelayEndId);
                mEvents.add(i, startDelayEndEvent);
                i += 2;
            } else {
                i++;
            }
        }

        if (!mEvents.isEmpty() && mEvents.get(0).mEvent != AnimationEvent.ANIMATION_START) {
            throw new UnsupportedOperationException(
                    "Sorting went bad, the start event should always be at index 0");
        }

        // Add AnimatorSet's start delay node to the beginning
        mEvents.add(0, new AnimationEvent(mRootNode, AnimationEvent.ANIMATION_START));
        mEvents.add(1, new AnimationEvent(mRootNode, AnimationEvent.ANIMATION_DELAY_ENDED));
        mEvents.add(2, new AnimationEvent(mRootNode, AnimationEvent.ANIMATION_END));

        if (mEvents.get(mEvents.size() - 1).mEvent == AnimationEvent.ANIMATION_START
                || mEvents.get(mEvents.size() - 1).mEvent == AnimationEvent.ANIMATION_DELAY_ENDED) {
            throw new UnsupportedOperationException(
                    "Something went wrong, the last event is not an end event");
        }
    }

    
Based on parent's start/end time, calculate children's start/end time. If cycle exists in the graph, all the nodes on the cycle will be marked to start at Animator.DURATION_INFINITE, meaning they will ever play. /**
     * Based on parent's start/end time, calculate children's start/end time. If cycle exists in
     * the graph, all the nodes on the cycle will be marked to start at {@link #DURATION_INFINITE},
     * meaning they will ever play.
     */
    private void updatePlayTime(Node parent,  ArrayList<Node> visited) {
        if (parent.mChildNodes == null) {
            if (parent == mRootNode) {
                // All the animators are in a cycle
                for (int i = 0; i < mNodes.size(); i++) {
                    Node node = mNodes.get(i);
                    if (node != mRootNode) {
                        node.mStartTime = DURATION_INFINITE;
                        node.mEndTime = DURATION_INFINITE;
                    }
                }
            }
            return;
        }

        visited.add(parent);
        int childrenSize = parent.mChildNodes.size();
        for (int i = 0; i < childrenSize; i++) {
            Node child = parent.mChildNodes.get(i);
            child.mTotalDuration = child.mAnimation.getTotalDuration();  // Update cached duration.

            int index = visited.indexOf(child);
            if (index >= 0) {
                // Child has been visited, cycle found. Mark all the nodes in the cycle.
                for (int j = index; j < visited.size(); j++) {
                    visited.get(j).mLatestParent = null;
                    visited.get(j).mStartTime = DURATION_INFINITE;
                    visited.get(j).mEndTime = DURATION_INFINITE;
                }
                child.mStartTime = DURATION_INFINITE;
                child.mEndTime = DURATION_INFINITE;
                child.mLatestParent = null;
                Log.w(TAG, "Cycle found in AnimatorSet: " + this);
                continue;
            }

            if (child.mStartTime != DURATION_INFINITE) {
                if (parent.mEndTime == DURATION_INFINITE) {
                    child.mLatestParent = parent;
                    child.mStartTime = DURATION_INFINITE;
                    child.mEndTime = DURATION_INFINITE;
                } else {
                    if (parent.mEndTime >= child.mStartTime) {
                        child.mLatestParent = parent;
                        child.mStartTime = parent.mEndTime;
                    }

                    child.mEndTime = child.mTotalDuration == DURATION_INFINITE
                            ? DURATION_INFINITE : child.mStartTime + child.mTotalDuration;
                }
            }
            updatePlayTime(child, visited);
        }
        visited.remove(parent);
    }

    // Recursively find all the siblings
    private void findSiblings(Node node, ArrayList<Node> siblings) {
        if (!siblings.contains(node)) {
            siblings.add(node);
            if (node.mSiblings == null) {
                return;
            }
            for (int i = 0; i < node.mSiblings.size(); i++) {
                findSiblings(node.mSiblings.get(i), siblings);
            }
        }
    }

    
@hide

TODO: For animatorSet defined in XML, we can use a flag to indicate what the play order
if defined (i.e. sequential or together), then we can use the flag instead of calculating
dynamically. Note that when AnimatorSet is empty this method returns true.
Returns:
whether all the animators in the set are supposed to play together/**
     * @hide
     * TODO: For animatorSet defined in XML, we can use a flag to indicate what the play order
     * if defined (i.e. sequential or together), then we can use the flag instead of calculating
     * dynamically. Note that when AnimatorSet is empty this method returns true.
     * @return whether all the animators in the set are supposed to play together
     */
    public boolean shouldPlayTogether() {
        updateAnimatorsDuration();
        createDependencyGraph();
        // All the child nodes are set out to play right after the delay animation
        return mRootNode.mChildNodes == null || mRootNode.mChildNodes.size() == mNodes.size() - 1;
    }

    @Override
    public long getTotalDuration() {
        updateAnimatorsDuration();
        createDependencyGraph();
        return mTotalDuration;
    }

    private Node getNodeForAnimation(Animator anim) {
        Node node = mNodeMap.get(anim);
        if (node == null) {
            node = new Node(anim);
            mNodeMap.put(anim, node);
            mNodes.add(node);
        }
        return node;
    }

    
A Node is an embodiment of both the Animator that it wraps as well as
any dependencies that are associated with that Animation. This includes
both dependencies upon other nodes (in the dependencies list) as
well as dependencies of other nodes upon this (in the nodeDependents list).
/**
     * A Node is an embodiment of both the Animator that it wraps as well as
     * any dependencies that are associated with that Animation. This includes
     * both dependencies upon other nodes (in the dependencies list) as
     * well as dependencies of other nodes upon this (in the nodeDependents list).
     */
    private static class Node implements Cloneable {
        Animator mAnimation;

        
Child nodes are the nodes associated with animations that will be played immediately
after current node.
/**
         * Child nodes are the nodes associated with animations that will be played immediately
         * after current node.
         */
        ArrayList<Node> mChildNodes = null;

        
Flag indicating whether the animation in this node is finished. This flag
is used by AnimatorSet to check, as each animation ends, whether all child animations
are mEnded and it's time to send out an end event for the entire AnimatorSet.
/**
         * Flag indicating whether the animation in this node is finished. This flag
         * is used by AnimatorSet to check, as each animation ends, whether all child animations
         * are mEnded and it's time to send out an end event for the entire AnimatorSet.
         */
        boolean mEnded = false;

        
Nodes with animations that are defined to play simultaneously with the animation
associated with this current node.
/**
         * Nodes with animations that are defined to play simultaneously with the animation
         * associated with this current node.
         */
        ArrayList<Node> mSiblings;

        
Parent nodes are the nodes with animations preceding current node's animation. Parent
nodes here are derived from user defined animation sequence.
/**
         * Parent nodes are the nodes with animations preceding current node's animation. Parent
         * nodes here are derived from user defined animation sequence.
         */
        ArrayList<Node> mParents;

        
Latest parent is the parent node associated with a animation that finishes after all
the other parents' animations.
/**
         * Latest parent is the parent node associated with a animation that finishes after all
         * the other parents' animations.
         */
        Node mLatestParent = null;

        boolean mParentsAdded = false;
        long mStartTime = 0;
        long mEndTime = 0;
        long mTotalDuration = 0;

        
Constructs the Node with the animation that it encapsulates. A Node has no
dependencies by default; dependencies are added via the addDependency()
method.
Params:
animation – The animation that the Node encapsulates./**
         * Constructs the Node with the animation that it encapsulates. A Node has no
         * dependencies by default; dependencies are added via the addDependency()
         * method.
         *
         * @param animation The animation that the Node encapsulates.
         */
        public Node(Animator animation) {
            this.mAnimation = animation;
        }

        @Override
        public Node clone() {
            try {
                Node node = (Node) super.clone();
                node.mAnimation = mAnimation.clone();
                if (mChildNodes != null) {
                    node.mChildNodes = new ArrayList<>(mChildNodes);
                }
                if (mSiblings != null) {
                    node.mSiblings = new ArrayList<>(mSiblings);
                }
                if (mParents != null) {
                    node.mParents = new ArrayList<>(mParents);
                }
                node.mEnded = false;
                return node;
            } catch (CloneNotSupportedException e) {
               throw new AssertionError();
            }
        }

        void addChild(Node node) {
            if (mChildNodes == null) {
                mChildNodes = new ArrayList<>();
            }
            if (!mChildNodes.contains(node)) {
                mChildNodes.add(node);
                node.addParent(this);
            }
        }

        public void addSibling(Node node) {
            if (mSiblings == null) {
                mSiblings = new ArrayList<Node>();
            }
            if (!mSiblings.contains(node)) {
                mSiblings.add(node);
                node.addSibling(this);
            }
        }

        public void addParent(Node node) {
            if (mParents == null) {
                mParents =  new ArrayList<Node>();
            }
            if (!mParents.contains(node)) {
                mParents.add(node);
                node.addChild(this);
            }
        }

        public void addParents(ArrayList<Node> parents) {
            if (parents == null) {
                return;
            }
            int size = parents.size();
            for (int i = 0; i < size; i++) {
                addParent(parents.get(i));
            }
        }
    }

    
This class is a wrapper around a node and an event for the animation corresponding to the
node. The 3 types of events represent the start of an animation, the end of a start delay of
an animation, and the end of an animation. When playing forward (i.e. in the non-reverse
direction), start event marks when start() should be called, and end event corresponds to
when the animation should finish. When playing in reverse, start delay will not be a part
of the animation. Therefore, reverse() is called at the end event, and animation should end
at the delay ended event.
/**
     * This class is a wrapper around a node and an event for the animation corresponding to the
     * node. The 3 types of events represent the start of an animation, the end of a start delay of
     * an animation, and the end of an animation. When playing forward (i.e. in the non-reverse
     * direction), start event marks when start() should be called, and end event corresponds to
     * when the animation should finish. When playing in reverse, start delay will not be a part
     * of the animation. Therefore, reverse() is called at the end event, and animation should end
     * at the delay ended event.
     */
    private static class AnimationEvent {
        static final int ANIMATION_START = 0;
        static final int ANIMATION_DELAY_ENDED = 1;
        static final int ANIMATION_END = 2;
        final Node mNode;
        final int mEvent;

        AnimationEvent(Node node, int event) {
            mNode = node;
            mEvent = event;
        }

        long getTime() {
            if (mEvent == ANIMATION_START) {
                return mNode.mStartTime;
            } else if (mEvent == ANIMATION_DELAY_ENDED) {
                return mNode.mStartTime == DURATION_INFINITE
                        ? DURATION_INFINITE : mNode.mStartTime + mNode.mAnimation.getStartDelay();
            } else {
                return mNode.mEndTime;
            }
        }

        public String toString() {
            String eventStr = mEvent == ANIMATION_START ? "start" : (
                    mEvent == ANIMATION_DELAY_ENDED ? "delay ended" : "end");
            return eventStr + " " + mNode.mAnimation.toString();
        }
    }

    private class SeekState {
        private long mPlayTime = -1;
        private boolean mSeekingInReverse = false;
        void reset() {
            mPlayTime = -1;
            mSeekingInReverse = false;
        }

        void setPlayTime(long playTime, boolean inReverse) {
            // TODO: This can be simplified.

            // Clamp the play time
            if (getTotalDuration() != DURATION_INFINITE) {
                mPlayTime = Math.min(playTime, getTotalDuration() - mStartDelay);
            }
            mPlayTime = Math.max(0, mPlayTime);
            mSeekingInReverse = inReverse;
        }

        void updateSeekDirection(boolean inReverse) {
            // Change seek direction without changing the overall fraction
            if (inReverse && getTotalDuration() == DURATION_INFINITE) {
                throw new UnsupportedOperationException("Error: Cannot reverse infinite animator"
                        + " set");
            }
            if (mPlayTime >= 0) {
                if (inReverse != mSeekingInReverse) {
                    mPlayTime = getTotalDuration() - mStartDelay - mPlayTime;
                    mSeekingInReverse = inReverse;
                }
            }
        }

        long getPlayTime() {
            return mPlayTime;
        }

        
Returns the playtime assuming the animation is forward playing
/**
         * Returns the playtime assuming the animation is forward playing
         */
        long getPlayTimeNormalized() {
            if (mReversing) {
                return getTotalDuration() - mStartDelay - mPlayTime;
            }
            return mPlayTime;
        }

        boolean isActive() {
            return mPlayTime != -1;
        }
    }

    
The Builder object is a utility class to facilitate adding animations to a
AnimatorSet along with the relationships between the various animations. The
intention of the Builder methods, along with the play() method of AnimatorSet is to make it possible to express the dependency relationships of animations in a natural way. Developers can also use the playTogether() and playSequentially() methods if these suit the need, but it might be easier in some situations to express the AnimatorSet of animations in pairs. 

The Builder object cannot be constructed directly, but is rather constructed internally via a call to AnimatorSet.play(Animator).

For example, this sets up a AnimatorSet to play anim1 and anim2 at the same time, anim3 to
play when anim2 finishes, and anim4 to play when anim3 finishes:
    AnimatorSet s = new AnimatorSet();
    s.play(anim1).with(anim2);
    s.play(anim2).before(anim3);
    s.play(anim4).after(anim3);


Note in the example that both before(Animator) and after(Animator) are used. These are just different ways of expressing the same relationship and are provided to make it easier to say things in a way that is more natural, depending on the situation.

It is possible to make several calls into the same Builder object to express multiple relationships. However, note that it is only the animation passed into the initial AnimatorSet.play(Animator) method that is the dependency in any of the successive calls to the Builder object. For example, the following code starts both anim2
and anim3 when anim1 ends; there is no direct dependency relationship between anim2 and
anim3:
  AnimatorSet s = new AnimatorSet();
  s.play(anim1).before(anim2).before(anim3);

If the desired result is to play anim1 then anim2 then anim3, this code expresses the
relationship correctly:

  AnimatorSet s = new AnimatorSet();
  s.play(anim1).before(anim2);
  s.play(anim2).before(anim3);


Note that it is possible to express relationships that cannot be resolved and will not
result in sensible results. For example, play(anim1).after(anim1) makes no
sense. In general, circular dependencies like this one (or more indirect ones where a depends
on b, which depends on c, which depends on a) should be avoided. Only create AnimatorSets
that can boil down to a simple, one-way relationship of animations starting with, before, and
after other, different, animations.
/**
     * The <code>Builder</code> object is a utility class to facilitate adding animations to a
     * <code>AnimatorSet</code> along with the relationships between the various animations. The
     * intention of the <code>Builder</code> methods, along with the {@link
     * AnimatorSet#play(Animator) play()} method of <code>AnimatorSet</code> is to make it possible
     * to express the dependency relationships of animations in a natural way. Developers can also
     * use the {@link AnimatorSet#playTogether(Animator[]) playTogether()} and {@link
     * AnimatorSet#playSequentially(Animator[]) playSequentially()} methods if these suit the need,
     * but it might be easier in some situations to express the AnimatorSet of animations in pairs.
     * <p/>
     * <p>The <code>Builder</code> object cannot be constructed directly, but is rather constructed
     * internally via a call to {@link AnimatorSet#play(Animator)}.</p>
     * <p/>
     * <p>For example, this sets up a AnimatorSet to play anim1 and anim2 at the same time, anim3 to
     * play when anim2 finishes, and anim4 to play when anim3 finishes:</p>
     * <pre>
     *     AnimatorSet s = new AnimatorSet();
     *     s.play(anim1).with(anim2);
     *     s.play(anim2).before(anim3);
     *     s.play(anim4).after(anim3);
     * </pre>
     * <p/>
     * <p>Note in the example that both {@link Builder#before(Animator)} and {@link
     * Builder#after(Animator)} are used. These are just different ways of expressing the same
     * relationship and are provided to make it easier to say things in a way that is more natural,
     * depending on the situation.</p>
     * <p/>
     * <p>It is possible to make several calls into the same <code>Builder</code> object to express
     * multiple relationships. However, note that it is only the animation passed into the initial
     * {@link AnimatorSet#play(Animator)} method that is the dependency in any of the successive
     * calls to the <code>Builder</code> object. For example, the following code starts both anim2
     * and anim3 when anim1 ends; there is no direct dependency relationship between anim2 and
     * anim3:
     * <pre>
     *   AnimatorSet s = new AnimatorSet();
     *   s.play(anim1).before(anim2).before(anim3);
     * </pre>
     * If the desired result is to play anim1 then anim2 then anim3, this code expresses the
     * relationship correctly:</p>
     * <pre>
     *   AnimatorSet s = new AnimatorSet();
     *   s.play(anim1).before(anim2);
     *   s.play(anim2).before(anim3);
     * </pre>
     * <p/>
     * <p>Note that it is possible to express relationships that cannot be resolved and will not
     * result in sensible results. For example, <code>play(anim1).after(anim1)</code> makes no
     * sense. In general, circular dependencies like this one (or more indirect ones where a depends
     * on b, which depends on c, which depends on a) should be avoided. Only create AnimatorSets
     * that can boil down to a simple, one-way relationship of animations starting with, before, and
     * after other, different, animations.</p>
     */
    public class Builder {

        
This tracks the current node being processed. It is supplied to the play() method
of AnimatorSet and passed into the constructor of Builder.
/**
         * This tracks the current node being processed. It is supplied to the play() method
         * of AnimatorSet and passed into the constructor of Builder.
         */
        private Node mCurrentNode;

        
package-private constructor. Builders are only constructed by AnimatorSet, when the
play() method is called.
Params:
anim – The animation that is the dependency for the other animations passed into
the other methods of this Builder object./**
         * package-private constructor. Builders are only constructed by AnimatorSet, when the
         * play() method is called.
         *
         * @param anim The animation that is the dependency for the other animations passed into
         * the other methods of this Builder object.
         */
        Builder(Animator anim) {
            mDependencyDirty = true;
            mCurrentNode = getNodeForAnimation(anim);
        }

        
Sets up the given animation to play at the same time as the animation supplied in the AnimatorSet.play(Animator) call that created this Builder object.
Params:
anim – The animation that will play when the animation supplied to the AnimatorSet.play(Animator) method starts./**
         * Sets up the given animation to play at the same time as the animation supplied in the
         * {@link AnimatorSet#play(Animator)} call that created this <code>Builder</code> object.
         *
         * @param anim The animation that will play when the animation supplied to the
         * {@link AnimatorSet#play(Animator)} method starts.
         */
        public Builder with(Animator anim) {
            Node node = getNodeForAnimation(anim);
            mCurrentNode.addSibling(node);
            return this;
        }

        
Sets up the given animation to play when the animation supplied in the AnimatorSet.play(Animator) call that created this Builder object
ends.
Params:
anim – The animation that will play when the animation supplied to the AnimatorSet.play(Animator) method ends./**
         * Sets up the given animation to play when the animation supplied in the
         * {@link AnimatorSet#play(Animator)} call that created this <code>Builder</code> object
         * ends.
         *
         * @param anim The animation that will play when the animation supplied to the
         * {@link AnimatorSet#play(Animator)} method ends.
         */
        public Builder before(Animator anim) {
            Node node = getNodeForAnimation(anim);
            mCurrentNode.addChild(node);
            return this;
        }

        
Sets up the given animation to play when the animation supplied in the AnimatorSet.play(Animator) call that created this Builder object
to start when the animation supplied in this method call ends.
Params:
anim – The animation whose end will cause the animation supplied to the AnimatorSet.play(Animator) method to play./**
         * Sets up the given animation to play when the animation supplied in the
         * {@link AnimatorSet#play(Animator)} call that created this <code>Builder</code> object
         * to start when the animation supplied in this method call ends.
         *
         * @param anim The animation whose end will cause the animation supplied to the
         * {@link AnimatorSet#play(Animator)} method to play.
         */
        public Builder after(Animator anim) {
            Node node = getNodeForAnimation(anim);
            mCurrentNode.addParent(node);
            return this;
        }

        
Sets up the animation supplied in the AnimatorSet.play(Animator) call that created this Builder object
to play when the given amount of time elapses.
Params:
delay – The number of milliseconds that should elapse before the
animation starts./**
         * Sets up the animation supplied in the
         * {@link AnimatorSet#play(Animator)} call that created this <code>Builder</code> object
         * to play when the given amount of time elapses.
         *
         * @param delay The number of milliseconds that should elapse before the
         * animation starts.
         */
        public Builder after(long delay) {
            // setup dummy ValueAnimator just to run the clock
            ValueAnimator anim = ValueAnimator.ofFloat(0f, 1f);
            anim.setDuration(delay);
            after(anim);
            return this;
        }

    }

}