https://source.android.com/ 
/*
 * 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.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.view.ViewTreeObserver;
import android.view.animation.AccelerateDecelerateInterpolator;
import android.view.animation.DecelerateInterpolator;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;


This class enables automatic animations on layout changes in ViewGroup objects. To enable transitions for a layout container, create a LayoutTransition object and set it on any ViewGroup by calling ViewGroup.setLayoutTransition(LayoutTransition). This will cause default animations to run whenever items are added to or removed from that container. To specify custom animations, use the 
setAnimator() method. 
One of the core concepts of these transition animations is that there are two types of
changes that cause the transition and four different animations that run because of
those changes. The changes that trigger the transition are items being added to a container
(referred to as an "appearing" transition) or removed from a container (also known as
"disappearing"). Setting the visibility of views (between GONE and VISIBLE) will trigger
the same add/remove logic. The animations that run due to those events are one that animates
items being added, one that animates items being removed, and two that animate the other
items in the container that change due to the add/remove occurrence. Users of
the transition may want different animations for the changing items depending on whether
they are changing due to an appearing or disappearing event, so there is one animation for
each of these variations of the changing event. Most of the API of this class is concerned
with setting up the basic properties of the animations used in these four situations,
or with setting up custom animations for any or all of the four.


By default, the DISAPPEARING animation begins immediately, as does the CHANGE_APPEARING animation. The other animations begin after a delay that is set to the default duration of the animations. This behavior facilitates a sequence of animations in transitions as follows: when an item is being added to a layout, the other children of that container will move first (thus creating space for the new item), then the appearing animation will run to animate the item being added. Conversely, when an item is removed from a container, the animation to remove it will run first, then the animations of the other children in the layout will run (closing the gap created in the layout when the item was removed). If this default choreography behavior is not desired, the setDuration(int, long) and setStartDelay(int, long) of any or all of the animations can be changed as appropriate. Keep in mind, however, that if you start an APPEARING animation before a DISAPPEARING animation is completed, the DISAPPEARING animation stops, and any effects from the DISAPPEARING animation are reverted. If you instead start a DISAPPEARING animation before an APPEARING animation is completed, a similar set of effects occurs for the APPEARING animation.


The animations specified for the transition, both the defaults and any custom animations
set on the transition object, are templates only. That is, these animations exist to hold the
basic animation properties, such as the duration, start delay, and properties being animated.
But the actual target object, as well as the start and end values for those properties, are
set automatically in the process of setting up the transition each time it runs. Each of the
animations is cloned from the original copy and the clone is then populated with the dynamic
values of the target being animated (such as one of the items in a layout container that is
moving as a result of the layout event) as well as the values that are changing (such as the
position and size of that object). The actual values that are pushed to each animation
depends on what properties are specified for the animation. For example, the default
CHANGE_APPEARING animation animates the left, top, right,
bottom, scrollX, and scrollY properties.
Values for these properties are updated with the pre- and post-layout
values when the transition begins. Custom animations will be similarly populated with
the target and values being animated, assuming they use ObjectAnimator objects with
property names that are known on the target object.


This class, and the associated XML flag for containers, animateLayoutChanges="true",
provides a simple utility meant for automating changes in straightforward situations.
Using LayoutTransition at multiple levels of a nested view hierarchy may not work due to the
interrelationship of the various levels of layout. Also, a container that is being scrolled
at the same time as items are being added or removed is probably not a good candidate for
this utility, because the before/after locations calculated by LayoutTransition
may not match the actual locations when the animations finish due to the container
being scrolled as the animations are running. You can work around that
particular issue by disabling the 'changing' animations by setting the CHANGE_APPEARING
and CHANGE_DISAPPEARING animations to null, and setting the startDelay of the
other animations appropriately.


/**
 * This class enables automatic animations on layout changes in ViewGroup objects. To enable
 * transitions for a layout container, create a LayoutTransition object and set it on any
 * ViewGroup by calling {@link ViewGroup#setLayoutTransition(LayoutTransition)}. This will cause
 * default animations to run whenever items are added to or removed from that container. To specify
 * custom animations, use the {@link LayoutTransition#setAnimator(int, Animator)
 * setAnimator()} method.
 *
 * <p>One of the core concepts of these transition animations is that there are two types of
 * changes that cause the transition and four different animations that run because of
 * those changes. The changes that trigger the transition are items being added to a container
 * (referred to as an "appearing" transition) or removed from a container (also known as
 * "disappearing"). Setting the visibility of views (between GONE and VISIBLE) will trigger
 * the same add/remove logic. The animations that run due to those events are one that animates
 * items being added, one that animates items being removed, and two that animate the other
 * items in the container that change due to the add/remove occurrence. Users of
 * the transition may want different animations for the changing items depending on whether
 * they are changing due to an appearing or disappearing event, so there is one animation for
 * each of these variations of the changing event. Most of the API of this class is concerned
 * with setting up the basic properties of the animations used in these four situations,
 * or with setting up custom animations for any or all of the four.</p>
 *
 * <p>By default, the DISAPPEARING animation begins immediately, as does the CHANGE_APPEARING
 * animation. The other animations begin after a delay that is set to the default duration
 * of the animations. This behavior facilitates a sequence of animations in transitions as
 * follows: when an item is being added to a layout, the other children of that container will
 * move first (thus creating space for the new item), then the appearing animation will run to
 * animate the item being added. Conversely, when an item is removed from a container, the
 * animation to remove it will run first, then the animations of the other children in the
 * layout will run (closing the gap created in the layout when the item was removed). If this
 * default choreography behavior is not desired, the {@link #setDuration(int, long)} and
 * {@link #setStartDelay(int, long)} of any or all of the animations can be changed as
 * appropriate. Keep in mind, however, that if you start an APPEARING animation before a
 * DISAPPEARING animation is completed, the DISAPPEARING animation stops, and any effects from
 * the DISAPPEARING animation are reverted. If you instead start a DISAPPEARING animation
 * before an APPEARING animation is completed, a similar set of effects occurs for the
 * APPEARING animation.</p>
 *
 * <p>The animations specified for the transition, both the defaults and any custom animations
 * set on the transition object, are templates only. That is, these animations exist to hold the
 * basic animation properties, such as the duration, start delay, and properties being animated.
 * But the actual target object, as well as the start and end values for those properties, are
 * set automatically in the process of setting up the transition each time it runs. Each of the
 * animations is cloned from the original copy and the clone is then populated with the dynamic
 * values of the target being animated (such as one of the items in a layout container that is
 * moving as a result of the layout event) as well as the values that are changing (such as the
 * position and size of that object). The actual values that are pushed to each animation
 * depends on what properties are specified for the animation. For example, the default
 * CHANGE_APPEARING animation animates the <code>left</code>, <code>top</code>, <code>right</code>,
 * <code>bottom</code>, <code>scrollX</code>, and <code>scrollY</code> properties.
 * Values for these properties are updated with the pre- and post-layout
 * values when the transition begins. Custom animations will be similarly populated with
 * the target and values being animated, assuming they use ObjectAnimator objects with
 * property names that are known on the target object.</p>
 *
 * <p>This class, and the associated XML flag for containers, animateLayoutChanges="true",
 * provides a simple utility meant for automating changes in straightforward situations.
 * Using LayoutTransition at multiple levels of a nested view hierarchy may not work due to the
 * interrelationship of the various levels of layout. Also, a container that is being scrolled
 * at the same time as items are being added or removed is probably not a good candidate for
 * this utility, because the before/after locations calculated by LayoutTransition
 * may not match the actual locations when the animations finish due to the container
 * being scrolled as the animations are running. You can work around that
 * particular issue by disabling the 'changing' animations by setting the CHANGE_APPEARING
 * and CHANGE_DISAPPEARING animations to null, and setting the startDelay of the
 * other animations appropriately.</p>
 */
public class LayoutTransition {

    
A flag indicating the animation that runs on those items that are changing
due to a new item appearing in the container.

/**
     * A flag indicating the animation that runs on those items that are changing
     * due to a new item appearing in the container.
     */
    public static final int CHANGE_APPEARING = 0;

    
A flag indicating the animation that runs on those items that are changing
due to an item disappearing from the container.

/**
     * A flag indicating the animation that runs on those items that are changing
     * due to an item disappearing from the container.
     */
    public static final int CHANGE_DISAPPEARING = 1;

    
A flag indicating the animation that runs on those items that are appearing
in the container.

/**
     * A flag indicating the animation that runs on those items that are appearing
     * in the container.
     */
    public static final int APPEARING = 2;

    
A flag indicating the animation that runs on those items that are disappearing
from the container.

/**
     * A flag indicating the animation that runs on those items that are disappearing
     * from the container.
     */
    public static final int DISAPPEARING = 3;

    
A flag indicating the animation that runs on those items that are changing due to a layout change not caused by items being added to or removed from the container. This transition type is not enabled by default; it can be enabled via enableTransitionType(int). 
/**
     * A flag indicating the animation that runs on those items that are changing
     * due to a layout change not caused by items being added to or removed
     * from the container. This transition type is not enabled by default; it can be
     * enabled via {@link #enableTransitionType(int)}.
     */
    public static final int CHANGING = 4;

    
Private bit fields used to set the collection of enabled transition types for
mTransitionTypes.

/**
     * Private bit fields used to set the collection of enabled transition types for
     * mTransitionTypes.
     */
    private static final int FLAG_APPEARING             = 0x01;
    private static final int FLAG_DISAPPEARING          = 0x02;
    private static final int FLAG_CHANGE_APPEARING      = 0x04;
    private static final int FLAG_CHANGE_DISAPPEARING   = 0x08;
    private static final int FLAG_CHANGING              = 0x10;

    
These variables hold the animations that are currently used to run the transition effects.
These animations are set to defaults, but can be changed to custom animations by
calls to setAnimator().

/**
     * These variables hold the animations that are currently used to run the transition effects.
     * These animations are set to defaults, but can be changed to custom animations by
     * calls to setAnimator().
     */
    private Animator mDisappearingAnim = null;
    private Animator mAppearingAnim = null;
    private Animator mChangingAppearingAnim = null;
    private Animator mChangingDisappearingAnim = null;
    private Animator mChangingAnim = null;

    
These are the default animations, defined in the constructor, that will be used
unless the user specifies custom animations.

/**
     * These are the default animations, defined in the constructor, that will be used
     * unless the user specifies custom animations.
     */
    private static ObjectAnimator defaultChange;
    private static ObjectAnimator defaultChangeIn;
    private static ObjectAnimator defaultChangeOut;
    private static ObjectAnimator defaultFadeIn;
    private static ObjectAnimator defaultFadeOut;

    
The default duration used by all animations.

/**
     * The default duration used by all animations.
     */
    private static long DEFAULT_DURATION = 300;

    
The durations of the different animations

/**
     * The durations of the different animations
     */
    private long mChangingAppearingDuration = DEFAULT_DURATION;
    private long mChangingDisappearingDuration = DEFAULT_DURATION;
    private long mChangingDuration = DEFAULT_DURATION;
    private long mAppearingDuration = DEFAULT_DURATION;
    private long mDisappearingDuration = DEFAULT_DURATION;

    
The start delays of the different animations. Note that the default behavior of
the appearing item is the default duration, since it should wait for the items to move
before fading it. Same for the changing animation when disappearing; it waits for the item
to fade out before moving the other items.

/**
     * The start delays of the different animations. Note that the default behavior of
     * the appearing item is the default duration, since it should wait for the items to move
     * before fading it. Same for the changing animation when disappearing; it waits for the item
     * to fade out before moving the other items.
     */
    private long mAppearingDelay = DEFAULT_DURATION;
    private long mDisappearingDelay = 0;
    private long mChangingAppearingDelay = 0;
    private long mChangingDisappearingDelay = DEFAULT_DURATION;
    private long mChangingDelay = 0;

    
The inter-animation delays used on the changing animations

/**
     * The inter-animation delays used on the changing animations
     */
    private long mChangingAppearingStagger = 0;
    private long mChangingDisappearingStagger = 0;
    private long mChangingStagger = 0;

    
Static interpolators - these are stateless and can be shared across the instances

/**
     * Static interpolators - these are stateless and can be shared across the instances
     */
    private static TimeInterpolator ACCEL_DECEL_INTERPOLATOR =
            new AccelerateDecelerateInterpolator();
    private static TimeInterpolator DECEL_INTERPOLATOR = new DecelerateInterpolator();
    private static TimeInterpolator sAppearingInterpolator = ACCEL_DECEL_INTERPOLATOR;
    private static TimeInterpolator sDisappearingInterpolator = ACCEL_DECEL_INTERPOLATOR;
    private static TimeInterpolator sChangingAppearingInterpolator = DECEL_INTERPOLATOR;
    private static TimeInterpolator sChangingDisappearingInterpolator = DECEL_INTERPOLATOR;
    private static TimeInterpolator sChangingInterpolator = DECEL_INTERPOLATOR;

    
The default interpolators used for the animations

/**
     * The default interpolators used for the animations
     */
    private TimeInterpolator mAppearingInterpolator = sAppearingInterpolator;
    private TimeInterpolator mDisappearingInterpolator = sDisappearingInterpolator;
    private TimeInterpolator mChangingAppearingInterpolator = sChangingAppearingInterpolator;
    private TimeInterpolator mChangingDisappearingInterpolator = sChangingDisappearingInterpolator;
    private TimeInterpolator mChangingInterpolator = sChangingInterpolator;

    
These hashmaps are used to store the animations that are currently running as part of
the transition. The reason for this is that a further layout event should cause
existing animations to stop where they are prior to starting new animations. So
we cache all of the current animations in this map for possible cancellation on
another layout event. LinkedHashMaps are used to preserve the order in which animations
are inserted, so that we process events (such as setting up start values) in the same order.

/**
     * These hashmaps are used to store the animations that are currently running as part of
     * the transition. The reason for this is that a further layout event should cause
     * existing animations to stop where they are prior to starting new animations. So
     * we cache all of the current animations in this map for possible cancellation on
     * another layout event. LinkedHashMaps are used to preserve the order in which animations
     * are inserted, so that we process events (such as setting up start values) in the same order.
     */
    private final HashMap<View, Animator> pendingAnimations =
            new HashMap<View, Animator>();
    private final LinkedHashMap<View, Animator> currentChangingAnimations =
            new LinkedHashMap<View, Animator>();
    private final LinkedHashMap<View, Animator> currentAppearingAnimations =
            new LinkedHashMap<View, Animator>();
    private final LinkedHashMap<View, Animator> currentDisappearingAnimations =
            new LinkedHashMap<View, Animator>();

    
This hashmap is used to track the listeners that have been added to the children of
a container. When a layout change occurs, an animation is created for each View, so that
the pre-layout values can be cached in that animation. Then a listener is added to the
view to see whether the layout changes the bounds of that view. If so, the animation
is set with the final values and then run. If not, the animation is not started. When
the process of setting up and running all appropriate animations is done, we need to
remove these listeners and clear out the map.

/**
     * This hashmap is used to track the listeners that have been added to the children of
     * a container. When a layout change occurs, an animation is created for each View, so that
     * the pre-layout values can be cached in that animation. Then a listener is added to the
     * view to see whether the layout changes the bounds of that view. If so, the animation
     * is set with the final values and then run. If not, the animation is not started. When
     * the process of setting up and running all appropriate animations is done, we need to
     * remove these listeners and clear out the map.
     */
    private final HashMap<View, View.OnLayoutChangeListener> layoutChangeListenerMap =
            new HashMap<View, View.OnLayoutChangeListener>();

    
Used to track the current delay being assigned to successive animations as they are
started. This value is incremented for each new animation, then zeroed before the next
transition begins.

/**
     * Used to track the current delay being assigned to successive animations as they are
     * started. This value is incremented for each new animation, then zeroed before the next
     * transition begins.
     */
    private long staggerDelay;

    
These are the types of transition animations that the LayoutTransition is reacting
to. By default, appearing/disappearing and the change animations related to them are
enabled (not CHANGING).

/**
     * These are the types of transition animations that the LayoutTransition is reacting
     * to. By default, appearing/disappearing and the change animations related to them are
     * enabled (not CHANGING).
     */
    private int mTransitionTypes = FLAG_CHANGE_APPEARING | FLAG_CHANGE_DISAPPEARING |
            FLAG_APPEARING | FLAG_DISAPPEARING;
    
The set of listeners that should be notified when APPEARING/DISAPPEARING transitions
start and end.

/**
     * The set of listeners that should be notified when APPEARING/DISAPPEARING transitions
     * start and end.
     */
    private ArrayList<TransitionListener> mListeners;

    
Controls whether changing animations automatically animate the parent hierarchy as well.
This behavior prevents artifacts when wrap_content layouts snap to the end state as the
transition begins, causing visual glitches and clipping.
Default value is true.

/**
     * Controls whether changing animations automatically animate the parent hierarchy as well.
     * This behavior prevents artifacts when wrap_content layouts snap to the end state as the
     * transition begins, causing visual glitches and clipping.
     * Default value is true.
     */
    private boolean mAnimateParentHierarchy = true;


    
Constructs a LayoutTransition object. By default, the object will listen to layout
events on any ViewGroup that it is set on and will run default animations for each
type of layout event.

/**
     * Constructs a LayoutTransition object. By default, the object will listen to layout
     * events on any ViewGroup that it is set on and will run default animations for each
     * type of layout event.
     */
    public LayoutTransition() {
        if (defaultChangeIn == null) {
            // "left" is just a placeholder; we'll put real properties/values in when needed
            PropertyValuesHolder pvhLeft = PropertyValuesHolder.ofInt("left", 0, 1);
            PropertyValuesHolder pvhTop = PropertyValuesHolder.ofInt("top", 0, 1);
            PropertyValuesHolder pvhRight = PropertyValuesHolder.ofInt("right", 0, 1);
            PropertyValuesHolder pvhBottom = PropertyValuesHolder.ofInt("bottom", 0, 1);
            PropertyValuesHolder pvhScrollX = PropertyValuesHolder.ofInt("scrollX", 0, 1);
            PropertyValuesHolder pvhScrollY = PropertyValuesHolder.ofInt("scrollY", 0, 1);
            defaultChangeIn = ObjectAnimator.ofPropertyValuesHolder((Object)null,
                    pvhLeft, pvhTop, pvhRight, pvhBottom, pvhScrollX, pvhScrollY);
            defaultChangeIn.setDuration(DEFAULT_DURATION);
            defaultChangeIn.setStartDelay(mChangingAppearingDelay);
            defaultChangeIn.setInterpolator(mChangingAppearingInterpolator);
            defaultChangeOut = defaultChangeIn.clone();
            defaultChangeOut.setStartDelay(mChangingDisappearingDelay);
            defaultChangeOut.setInterpolator(mChangingDisappearingInterpolator);
            defaultChange = defaultChangeIn.clone();
            defaultChange.setStartDelay(mChangingDelay);
            defaultChange.setInterpolator(mChangingInterpolator);

            defaultFadeIn = ObjectAnimator.ofFloat(null, "alpha", 0f, 1f);
            defaultFadeIn.setDuration(DEFAULT_DURATION);
            defaultFadeIn.setStartDelay(mAppearingDelay);
            defaultFadeIn.setInterpolator(mAppearingInterpolator);
            defaultFadeOut = ObjectAnimator.ofFloat(null, "alpha", 1f, 0f);
            defaultFadeOut.setDuration(DEFAULT_DURATION);
            defaultFadeOut.setStartDelay(mDisappearingDelay);
            defaultFadeOut.setInterpolator(mDisappearingInterpolator);
        }
        mChangingAppearingAnim = defaultChangeIn;
        mChangingDisappearingAnim = defaultChangeOut;
        mChangingAnim = defaultChange;
        mAppearingAnim = defaultFadeIn;
        mDisappearingAnim = defaultFadeOut;
    }

    
Sets the duration to be used by all animations of this transition object. If you want to set the duration of just one of the animations in particular, use the setDuration(int, long) method. 
Params:
  • duration – The length of time, in milliseconds, that the transition animations
should last.
/**
     * Sets the duration to be used by all animations of this transition object. If you want to
     * set the duration of just one of the animations in particular, use the
     * {@link #setDuration(int, long)} method.
     *
     * @param duration The length of time, in milliseconds, that the transition animations
     * should last.
     */
    public void setDuration(long duration) {
        mChangingAppearingDuration = duration;
        mChangingDisappearingDuration = duration;
        mChangingDuration = duration;
        mAppearingDuration = duration;
        mDisappearingDuration = duration;
    }

    
Enables the specified transitionType for this LayoutTransition object. By default, a LayoutTransition listens for changes in children being added/remove/hidden/shown in the container, and runs the animations associated with those events. That is, all transition types besides CHANGING are enabled by default. You can also enable CHANGING animations by calling this method with the CHANGING transitionType. 
Params:
/**
     * Enables the specified transitionType for this LayoutTransition object.
     * By default, a LayoutTransition listens for changes in children being
     * added/remove/hidden/shown in the container, and runs the animations associated with
     * those events. That is, all transition types besides {@link #CHANGING} are enabled by default.
     * You can also enable {@link #CHANGING} animations by calling this method with the
     * {@link #CHANGING} transitionType.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}.
     */
    public void enableTransitionType(int transitionType) {
        switch (transitionType) {
            case APPEARING:
                mTransitionTypes |= FLAG_APPEARING;
                break;
            case DISAPPEARING:
                mTransitionTypes |= FLAG_DISAPPEARING;
                break;
            case CHANGE_APPEARING:
                mTransitionTypes |= FLAG_CHANGE_APPEARING;
                break;
            case CHANGE_DISAPPEARING:
                mTransitionTypes |= FLAG_CHANGE_DISAPPEARING;
                break;
            case CHANGING:
                mTransitionTypes |= FLAG_CHANGING;
                break;
        }
    }

    
Disables the specified transitionType for this LayoutTransition object. By default, all transition types except CHANGING are enabled. 
Params:
/**
     * Disables the specified transitionType for this LayoutTransition object.
     * By default, all transition types except {@link #CHANGING} are enabled.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}.
     */
    public void disableTransitionType(int transitionType) {
        switch (transitionType) {
            case APPEARING:
                mTransitionTypes &= ~FLAG_APPEARING;
                break;
            case DISAPPEARING:
                mTransitionTypes &= ~FLAG_DISAPPEARING;
                break;
            case CHANGE_APPEARING:
                mTransitionTypes &= ~FLAG_CHANGE_APPEARING;
                break;
            case CHANGE_DISAPPEARING:
                mTransitionTypes &= ~FLAG_CHANGE_DISAPPEARING;
                break;
            case CHANGING:
                mTransitionTypes &= ~FLAG_CHANGING;
                break;
        }
    }

    
Returns whether the specified transitionType is enabled for this LayoutTransition object. By default, all transition types except CHANGING are enabled. 
Params:
Returns:true if the specified transitionType is currently enabled, false otherwise.
/**
     * Returns whether the specified transitionType is enabled for this LayoutTransition object.
     * By default, all transition types except {@link #CHANGING} are enabled.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}.
     * @return true if the specified transitionType is currently enabled, false otherwise.
     */
    public boolean isTransitionTypeEnabled(int transitionType) {
        switch (transitionType) {
            case APPEARING:
                return (mTransitionTypes & FLAG_APPEARING) == FLAG_APPEARING;
            case DISAPPEARING:
                return (mTransitionTypes & FLAG_DISAPPEARING) == FLAG_DISAPPEARING;
            case CHANGE_APPEARING:
                return (mTransitionTypes & FLAG_CHANGE_APPEARING) == FLAG_CHANGE_APPEARING;
            case CHANGE_DISAPPEARING:
                return (mTransitionTypes & FLAG_CHANGE_DISAPPEARING) == FLAG_CHANGE_DISAPPEARING;
            case CHANGING:
                return (mTransitionTypes & FLAG_CHANGING) == FLAG_CHANGING;
        }
        return false;
    }

    
Sets the start delay on one of the animation objects used by this transition. The
transitionType parameter determines the animation whose start delay
is being set.

Params:
See Also:
/**
     * Sets the start delay on one of the animation objects used by this transition. The
     * <code>transitionType</code> parameter determines the animation whose start delay
     * is being set.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}, which determines
     * the animation whose start delay is being set.
     * @param delay The length of time, in milliseconds, to delay before starting the animation.
     * @see Animator#setStartDelay(long)
     */
    public void setStartDelay(int transitionType, long delay) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                mChangingAppearingDelay = delay;
                break;
            case CHANGE_DISAPPEARING:
                mChangingDisappearingDelay = delay;
                break;
            case CHANGING:
                mChangingDelay = delay;
                break;
            case APPEARING:
                mAppearingDelay = delay;
                break;
            case DISAPPEARING:
                mDisappearingDelay = delay;
                break;
        }
    }

    
Gets the start delay on one of the animation objects used by this transition. The
transitionType parameter determines the animation whose start delay
is returned.

Params:
See Also:
Returns:long The start delay of the specified animation.
/**
     * Gets the start delay on one of the animation objects used by this transition. The
     * <code>transitionType</code> parameter determines the animation whose start delay
     * is returned.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}, which determines
     * the animation whose start delay is returned.
     * @return long The start delay of the specified animation.
     * @see Animator#getStartDelay()
     */
    public long getStartDelay(int transitionType) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                return mChangingAppearingDelay;
            case CHANGE_DISAPPEARING:
                return mChangingDisappearingDelay;
            case CHANGING:
                return mChangingDelay;
            case APPEARING:
                return mAppearingDelay;
            case DISAPPEARING:
                return mDisappearingDelay;
        }
        // shouldn't reach here
        return 0;
    }

    
Sets the duration on one of the animation objects used by this transition. The
transitionType parameter determines the animation whose duration
is being set.

Params:
See Also:
/**
     * Sets the duration on one of the animation objects used by this transition. The
     * <code>transitionType</code> parameter determines the animation whose duration
     * is being set.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}, which determines
     * the animation whose duration is being set.
     * @param duration The length of time, in milliseconds, that the specified animation should run.
     * @see Animator#setDuration(long)
     */
    public void setDuration(int transitionType, long duration) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                mChangingAppearingDuration = duration;
                break;
            case CHANGE_DISAPPEARING:
                mChangingDisappearingDuration = duration;
                break;
            case CHANGING:
                mChangingDuration = duration;
                break;
            case APPEARING:
                mAppearingDuration = duration;
                break;
            case DISAPPEARING:
                mDisappearingDuration = duration;
                break;
        }
    }

    
Gets the duration on one of the animation objects used by this transition. The
transitionType parameter determines the animation whose duration
is returned.

Params:
See Also:
Returns:long The duration of the specified animation.
/**
     * Gets the duration on one of the animation objects used by this transition. The
     * <code>transitionType</code> parameter determines the animation whose duration
     * is returned.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}, which determines
     * the animation whose duration is returned.
     * @return long The duration of the specified animation.
     * @see Animator#getDuration()
     */
    public long getDuration(int transitionType) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                return mChangingAppearingDuration;
            case CHANGE_DISAPPEARING:
                return mChangingDisappearingDuration;
            case CHANGING:
                return mChangingDuration;
            case APPEARING:
                return mAppearingDuration;
            case DISAPPEARING:
                return mDisappearingDuration;
        }
        // shouldn't reach here
        return 0;
    }

    
Sets the length of time to delay between starting each animation during one of the
change animations.

Params:
/**
     * Sets the length of time to delay between starting each animation during one of the
     * change animations.
     *
     * @param transitionType A value of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING}, or
     * {@link #CHANGING}.
     * @param duration The length of time, in milliseconds, to delay before launching the next
     * animation in the sequence.
     */
    public void setStagger(int transitionType, long duration) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                mChangingAppearingStagger = duration;
                break;
            case CHANGE_DISAPPEARING:
                mChangingDisappearingStagger = duration;
                break;
            case CHANGING:
                mChangingStagger = duration;
                break;
            // noop other cases
        }
    }

    
Gets the length of time to delay between starting each animation during one of the
change animations.

Params:
Returns:long The length of time, in milliseconds, to delay before launching the next
animation in the sequence.
/**
     * Gets the length of time to delay between starting each animation during one of the
     * change animations.
     *
     * @param transitionType A value of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING}, or
     * {@link #CHANGING}.
     * @return long The length of time, in milliseconds, to delay before launching the next
     * animation in the sequence.
     */
    public long getStagger(int transitionType) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                return mChangingAppearingStagger;
            case CHANGE_DISAPPEARING:
                return mChangingDisappearingStagger;
            case CHANGING:
                return mChangingStagger;
        }
        // shouldn't reach here
        return 0;
    }

    
Sets the interpolator on one of the animation objects used by this transition. The
transitionType parameter determines the animation whose interpolator
is being set.

Params:
See Also:
/**
     * Sets the interpolator on one of the animation objects used by this transition. The
     * <code>transitionType</code> parameter determines the animation whose interpolator
     * is being set.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}, which determines
     * the animation whose interpolator is being set.
     * @param interpolator The interpolator that the specified animation should use.
     * @see Animator#setInterpolator(TimeInterpolator)
     */
    public void setInterpolator(int transitionType, TimeInterpolator interpolator) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                mChangingAppearingInterpolator = interpolator;
                break;
            case CHANGE_DISAPPEARING:
                mChangingDisappearingInterpolator = interpolator;
                break;
            case CHANGING:
                mChangingInterpolator = interpolator;
                break;
            case APPEARING:
                mAppearingInterpolator = interpolator;
                break;
            case DISAPPEARING:
                mDisappearingInterpolator = interpolator;
                break;
        }
    }

    
Gets the interpolator on one of the animation objects used by this transition. The
transitionType parameter determines the animation whose interpolator
is returned.

Params:
See Also:
Returns:TimeInterpolator The interpolator that the specified animation uses.
/**
     * Gets the interpolator on one of the animation objects used by this transition. The
     * <code>transitionType</code> parameter determines the animation whose interpolator
     * is returned.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}, which determines
     * the animation whose interpolator is being returned.
     * @return TimeInterpolator The interpolator that the specified animation uses.
     * @see Animator#setInterpolator(TimeInterpolator)
     */
    public TimeInterpolator getInterpolator(int transitionType) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                return mChangingAppearingInterpolator;
            case CHANGE_DISAPPEARING:
                return mChangingDisappearingInterpolator;
            case CHANGING:
                return mChangingInterpolator;
            case APPEARING:
                return mAppearingInterpolator;
            case DISAPPEARING:
                return mDisappearingInterpolator;
        }
        // shouldn't reach here
        return null;
    }

    
Sets the animation used during one of the transition types that may run. Any
Animator object can be used, but to be most useful in the context of layout
transitions, the animation should either be a ObjectAnimator or a AnimatorSet
of animations including PropertyAnimators. Also, these ObjectAnimator objects
should be able to get and set values on their target objects automatically. For
example, a ObjectAnimator that animates the property "left" is able to set and get the
left property from the View objects being animated by the layout
transition. The transition works by setting target objects and properties
dynamically, according to the pre- and post-layoout values of those objects, so
having animations that can handle those properties appropriately will work best
for custom animation. The dynamic setting of values is only the case for the
CHANGE animations; the APPEARING and DISAPPEARING animations are simply run with
the values they have.

It is also worth noting that any and all animations (and their underlying
PropertyValuesHolder objects) will have their start and end values set according
to the pre- and post-layout values. So, for example, a custom animation on "alpha"
as the CHANGE_APPEARING animation will inherit the real value of alpha on the target
object (presumably 1) as its starting and ending value when the animation begins.
Animations which need to use values at the beginning and end that may not match the
values queried when the transition begins may need to use a different mechanism
than a standard ObjectAnimator object.


Params:
/**
     * Sets the animation used during one of the transition types that may run. Any
     * Animator object can be used, but to be most useful in the context of layout
     * transitions, the animation should either be a ObjectAnimator or a AnimatorSet
     * of animations including PropertyAnimators. Also, these ObjectAnimator objects
     * should be able to get and set values on their target objects automatically. For
     * example, a ObjectAnimator that animates the property "left" is able to set and get the
     * <code>left</code> property from the View objects being animated by the layout
     * transition. The transition works by setting target objects and properties
     * dynamically, according to the pre- and post-layoout values of those objects, so
     * having animations that can handle those properties appropriately will work best
     * for custom animation. The dynamic setting of values is only the case for the
     * CHANGE animations; the APPEARING and DISAPPEARING animations are simply run with
     * the values they have.
     *
     * <p>It is also worth noting that any and all animations (and their underlying
     * PropertyValuesHolder objects) will have their start and end values set according
     * to the pre- and post-layout values. So, for example, a custom animation on "alpha"
     * as the CHANGE_APPEARING animation will inherit the real value of alpha on the target
     * object (presumably 1) as its starting and ending value when the animation begins.
     * Animations which need to use values at the beginning and end that may not match the
     * values queried when the transition begins may need to use a different mechanism
     * than a standard ObjectAnimator object.</p>
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}, which determines the
     * animation whose animator is being set.
     * @param animator The animation being assigned. A value of <code>null</code> means that no
     * animation will be run for the specified transitionType.
     */
    public void setAnimator(int transitionType, Animator animator) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                mChangingAppearingAnim = animator;
                break;
            case CHANGE_DISAPPEARING:
                mChangingDisappearingAnim = animator;
                break;
            case CHANGING:
                mChangingAnim = animator;
                break;
            case APPEARING:
                mAppearingAnim = animator;
                break;
            case DISAPPEARING:
                mDisappearingAnim = animator;
                break;
        }
    }

    
Gets the animation used during one of the transition types that may run.

Params:
See Also:
Returns:Animator The animation being used for the given transition type.
/**
     * Gets the animation used during one of the transition types that may run.
     *
     * @param transitionType One of {@link #CHANGE_APPEARING}, {@link #CHANGE_DISAPPEARING},
     * {@link #CHANGING}, {@link #APPEARING}, or {@link #DISAPPEARING}, which determines
     * the animation whose animator is being returned.
     * @return Animator The animation being used for the given transition type.
     * @see #setAnimator(int, Animator)
     */
    public Animator getAnimator(int transitionType) {
        switch (transitionType) {
            case CHANGE_APPEARING:
                return mChangingAppearingAnim;
            case CHANGE_DISAPPEARING:
                return mChangingDisappearingAnim;
            case CHANGING:
                return mChangingAnim;
            case APPEARING:
                return mAppearingAnim;
            case DISAPPEARING:
                return mDisappearingAnim;
        }
        // shouldn't reach here
        return null;
    }

    
This function sets up animations on all of the views that change during layout.
For every child in the parent, we create a change animation of the appropriate
type (appearing, disappearing, or changing) and ask it to populate its start values from its
target view. We add layout listeners to all child views and listen for changes. For
those views that change, we populate the end values for those animations and start them.
Animations are not run on unchanging views.

Params:
  • parent – The container which is undergoing a change.
  • newView – The view being added to or removed from the parent. May be null if the
changeReason is CHANGING.
  • changeReason – A value of APPEARING, DISAPPEARING, or CHANGING, indicating whether the
transition is occurring because an item is being added to or removed from the parent, or
if it is running in response to a layout operation (that is, if the value is CHANGING).
/**
     * This function sets up animations on all of the views that change during layout.
     * For every child in the parent, we create a change animation of the appropriate
     * type (appearing, disappearing, or changing) and ask it to populate its start values from its
     * target view. We add layout listeners to all child views and listen for changes. For
     * those views that change, we populate the end values for those animations and start them.
     * Animations are not run on unchanging views.
     *
     * @param parent The container which is undergoing a change.
     * @param newView The view being added to or removed from the parent. May be null if the
     * changeReason is CHANGING.
     * @param changeReason A value of APPEARING, DISAPPEARING, or CHANGING, indicating whether the
     * transition is occurring because an item is being added to or removed from the parent, or
     * if it is running in response to a layout operation (that is, if the value is CHANGING).
     */
    private void runChangeTransition(final ViewGroup parent, View newView, final int changeReason) {

        Animator baseAnimator = null;
        Animator parentAnimator = null;
        final long duration;
        switch (changeReason) {
            case APPEARING:
                baseAnimator = mChangingAppearingAnim;
                duration = mChangingAppearingDuration;
                parentAnimator = defaultChangeIn;
                break;
            case DISAPPEARING:
                baseAnimator = mChangingDisappearingAnim;
                duration = mChangingDisappearingDuration;
                parentAnimator = defaultChangeOut;
                break;
            case CHANGING:
                baseAnimator = mChangingAnim;
                duration = mChangingDuration;
                parentAnimator = defaultChange;
                break;
            default:
                // Shouldn't reach here
                duration = 0;
                break;
        }
        // If the animation is null, there's nothing to do
        if (baseAnimator == null) {
            return;
        }

        // reset the inter-animation delay, in case we use it later
        staggerDelay = 0;

        final ViewTreeObserver observer = parent.getViewTreeObserver();
        if (!observer.isAlive()) {
            // If the observer's not in a good state, skip the transition
            return;
        }
        int numChildren = parent.getChildCount();

        for (int i = 0; i < numChildren; ++i) {
            final View child = parent.getChildAt(i);

            // only animate the views not being added or removed
            if (child != newView) {
                setupChangeAnimation(parent, changeReason, baseAnimator, duration, child);
            }
        }
        if (mAnimateParentHierarchy) {
            ViewGroup tempParent = parent;
            while (tempParent != null) {
                ViewParent parentParent = tempParent.getParent();
                if (parentParent instanceof ViewGroup) {
                    setupChangeAnimation((ViewGroup)parentParent, changeReason, parentAnimator,
                            duration, tempParent);
                    tempParent = (ViewGroup) parentParent;
                } else {
                    tempParent = null;
                }

            }
        }

        // This is the cleanup step. When we get this rendering event, we know that all of
        // the appropriate animations have been set up and run. Now we can clear out the
        // layout listeners.
        CleanupCallback callback = new CleanupCallback(layoutChangeListenerMap, parent);
        observer.addOnPreDrawListener(callback);
        parent.addOnAttachStateChangeListener(callback);
    }

    
This flag controls whether CHANGE_APPEARING or CHANGE_DISAPPEARING animations will
cause the default changing animation to be run on the parent hierarchy as well. This allows
containers of transitioning views to also transition, which may be necessary in situations
where the containers bounds change between the before/after states and may clip their
children during the transition animations. For example, layouts with wrap_content will
adjust their bounds according to the dimensions of their children.

The default changing transitions animate the bounds and scroll positions of the
target views. These are the animations that will run on the parent hierarchy, not
the custom animations that happen to be set on the transition. This allows custom
behavior for the children of the transitioning container, but uses standard behavior
of resizing/rescrolling on any changing parents.

Params:
  • animateParentHierarchy – A boolean value indicating whether the parents of
transitioning views should also be animated during the transition. Default value is true.
/**
     * This flag controls whether CHANGE_APPEARING or CHANGE_DISAPPEARING animations will
     * cause the default changing animation to be run on the parent hierarchy as well. This allows
     * containers of transitioning views to also transition, which may be necessary in situations
     * where the containers bounds change between the before/after states and may clip their
     * children during the transition animations. For example, layouts with wrap_content will
     * adjust their bounds according to the dimensions of their children.
     *
     * <p>The default changing transitions animate the bounds and scroll positions of the
     * target views. These are the animations that will run on the parent hierarchy, not
     * the custom animations that happen to be set on the transition. This allows custom
     * behavior for the children of the transitioning container, but uses standard behavior
     * of resizing/rescrolling on any changing parents.
     *
     * @param animateParentHierarchy A boolean value indicating whether the parents of
     * transitioning views should also be animated during the transition. Default value is true.
     */
    public void setAnimateParentHierarchy(boolean animateParentHierarchy) {
        mAnimateParentHierarchy = animateParentHierarchy;
    }

    
Utility function called by runChangingTransition for both the children and the parent
hierarchy.

/**
     * Utility function called by runChangingTransition for both the children and the parent
     * hierarchy.
     */
    private void setupChangeAnimation(final ViewGroup parent, final int changeReason,
            Animator baseAnimator, final long duration, final View child) {

        // If we already have a listener for this child, then we've already set up the
        // changing animation we need. Multiple calls for a child may occur when several
        // add/remove operations are run at once on a container; each one will trigger
        // changes for the existing children in the container.
        if (layoutChangeListenerMap.get(child) != null) {
            return;
        }

        // Don't animate items up from size(0,0); this is likely because the objects
        // were offscreen/invisible or otherwise measured to be infinitely small. We don't
        // want to see them animate into their real size; just ignore animation requests
        // on these views
        if (child.getWidth() == 0 && child.getHeight() == 0) {
            return;
        }

        // Make a copy of the appropriate animation
        final Animator anim = baseAnimator.clone();

        // Set the target object for the animation
        anim.setTarget(child);

        // A ObjectAnimator (or AnimatorSet of them) can extract start values from
        // its target object
        anim.setupStartValues();

        // If there's an animation running on this view already, cancel it
        Animator currentAnimation = pendingAnimations.get(child);
        if (currentAnimation != null) {
            currentAnimation.cancel();
            pendingAnimations.remove(child);
        }
        // Cache the animation in case we need to cancel it later
        pendingAnimations.put(child, anim);

        // For the animations which don't get started, we have to have a means of
        // removing them from the cache, lest we leak them and their target objects.
        // We run an animator for the default duration+100 (an arbitrary time, but one
        // which should far surpass the delay between setting them up here and
        // handling layout events which start them.
        ValueAnimator pendingAnimRemover = ValueAnimator.ofFloat(0f, 1f).
                setDuration(duration + 100);
        pendingAnimRemover.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                pendingAnimations.remove(child);
            }
        });
        pendingAnimRemover.start();

        // Add a listener to track layout changes on this view. If we don't get a callback,
        // then there's nothing to animate.
        final View.OnLayoutChangeListener listener = new View.OnLayoutChangeListener() {
            public void onLayoutChange(View v, int left, int top, int right, int bottom,
                    int oldLeft, int oldTop, int oldRight, int oldBottom) {

                // Tell the animation to extract end values from the changed object
                anim.setupEndValues();
                if (anim instanceof ValueAnimator) {
                    boolean valuesDiffer = false;
                    ValueAnimator valueAnim = (ValueAnimator)anim;
                    PropertyValuesHolder[] oldValues = valueAnim.getValues();
                    for (int i = 0; i < oldValues.length; ++i) {
                        PropertyValuesHolder pvh = oldValues[i];
                        if (pvh.mKeyframes instanceof KeyframeSet) {
                            KeyframeSet keyframeSet = (KeyframeSet) pvh.mKeyframes;
                            if (keyframeSet.mFirstKeyframe == null ||
                                    keyframeSet.mLastKeyframe == null ||
                                    !keyframeSet.mFirstKeyframe.getValue().equals(
                                            keyframeSet.mLastKeyframe.getValue())) {
                                valuesDiffer = true;
                            }
                        } else if (!pvh.mKeyframes.getValue(0).equals(pvh.mKeyframes.getValue(1))) {
                            valuesDiffer = true;
                        }
                    }
                    if (!valuesDiffer) {
                        return;
                    }
                }

                long startDelay = 0;
                switch (changeReason) {
                    case APPEARING:
                        startDelay = mChangingAppearingDelay + staggerDelay;
                        staggerDelay += mChangingAppearingStagger;
                        if (mChangingAppearingInterpolator != sChangingAppearingInterpolator) {
                            anim.setInterpolator(mChangingAppearingInterpolator);
                        }
                        break;
                    case DISAPPEARING:
                        startDelay = mChangingDisappearingDelay + staggerDelay;
                        staggerDelay += mChangingDisappearingStagger;
                        if (mChangingDisappearingInterpolator !=
                                sChangingDisappearingInterpolator) {
                            anim.setInterpolator(mChangingDisappearingInterpolator);
                        }
                        break;
                    case CHANGING:
                        startDelay = mChangingDelay + staggerDelay;
                        staggerDelay += mChangingStagger;
                        if (mChangingInterpolator != sChangingInterpolator) {
                            anim.setInterpolator(mChangingInterpolator);
                        }
                        break;
                }
                anim.setStartDelay(startDelay);
                anim.setDuration(duration);

                Animator prevAnimation = currentChangingAnimations.get(child);
                if (prevAnimation != null) {
                    prevAnimation.cancel();
                }
                Animator pendingAnimation = pendingAnimations.get(child);
                if (pendingAnimation != null) {
                    pendingAnimations.remove(child);
                }
                // Cache the animation in case we need to cancel it later
                currentChangingAnimations.put(child, anim);

                parent.requestTransitionStart(LayoutTransition.this);

                // this only removes listeners whose views changed - must clear the
                // other listeners later
                child.removeOnLayoutChangeListener(this);
                layoutChangeListenerMap.remove(child);
            }
        };
        // Remove the animation from the cache when it ends
        anim.addListener(new AnimatorListenerAdapter() {

            @Override
            public void onAnimationStart(Animator animator) {
                if (hasListeners()) {
                    ArrayList<TransitionListener> listeners =
                            (ArrayList<TransitionListener>) mListeners.clone();
                    for (TransitionListener listener : listeners) {
                        listener.startTransition(LayoutTransition.this, parent, child,
                                changeReason == APPEARING ?
                                        CHANGE_APPEARING : changeReason == DISAPPEARING ?
                                        CHANGE_DISAPPEARING : CHANGING);
                    }
                }
            }

            @Override
            public void onAnimationCancel(Animator animator) {
                child.removeOnLayoutChangeListener(listener);
                layoutChangeListenerMap.remove(child);
            }

            @Override
            public void onAnimationEnd(Animator animator) {
                currentChangingAnimations.remove(child);
                if (hasListeners()) {
                    ArrayList<TransitionListener> listeners =
                            (ArrayList<TransitionListener>) mListeners.clone();
                    for (TransitionListener listener : listeners) {
                        listener.endTransition(LayoutTransition.this, parent, child,
                                changeReason == APPEARING ?
                                        CHANGE_APPEARING : changeReason == DISAPPEARING ?
                                        CHANGE_DISAPPEARING : CHANGING);
                    }
                }
            }
        });

        child.addOnLayoutChangeListener(listener);
        // cache the listener for later removal
        layoutChangeListenerMap.put(child, listener);
    }

    
Starts the animations set up for a CHANGING transition. We separate the setup of these
animations from actually starting them, to avoid side-effects that starting the animations
may have on the properties of the affected objects. After setup, we tell the affected parent
that this transition should be started. The parent informs its ViewAncestor, which then
starts the transition after the current layout/measurement phase, just prior to drawing
the view hierarchy.

@hide
/**
     * Starts the animations set up for a CHANGING transition. We separate the setup of these
     * animations from actually starting them, to avoid side-effects that starting the animations
     * may have on the properties of the affected objects. After setup, we tell the affected parent
     * that this transition should be started. The parent informs its ViewAncestor, which then
     * starts the transition after the current layout/measurement phase, just prior to drawing
     * the view hierarchy.
     *
     * @hide
     */
    public void startChangingAnimations() {
        LinkedHashMap<View, Animator> currentAnimCopy =
                (LinkedHashMap<View, Animator>) currentChangingAnimations.clone();
        for (Animator anim : currentAnimCopy.values()) {
            if (anim instanceof ObjectAnimator) {
                ((ObjectAnimator) anim).setCurrentPlayTime(0);
            }
            anim.start();
        }
    }

    
Ends the animations that are set up for a CHANGING transition. This is a variant of
startChangingAnimations() which is called when the window the transition is playing in
is not visible. We need to make sure the animations put their targets in their end states
and that the transition finishes to remove any mid-process state (such as isRunning()).

@hide
/**
     * Ends the animations that are set up for a CHANGING transition. This is a variant of
     * startChangingAnimations() which is called when the window the transition is playing in
     * is not visible. We need to make sure the animations put their targets in their end states
     * and that the transition finishes to remove any mid-process state (such as isRunning()).
     *
     * @hide
     */
    public void endChangingAnimations() {
        LinkedHashMap<View, Animator> currentAnimCopy =
                (LinkedHashMap<View, Animator>) currentChangingAnimations.clone();
        for (Animator anim : currentAnimCopy.values()) {
            anim.start();
            anim.end();
        }
        // listeners should clean up the currentChangingAnimations list, but just in case...
        currentChangingAnimations.clear();
    }

    
Returns true if animations are running which animate layout-related properties. This
essentially means that either CHANGE_APPEARING or CHANGE_DISAPPEARING animations
are running, since these animations operate on layout-related properties.

Returns:true if CHANGE_APPEARING or CHANGE_DISAPPEARING animations are currently
running.
/**
     * Returns true if animations are running which animate layout-related properties. This
     * essentially means that either CHANGE_APPEARING or CHANGE_DISAPPEARING animations
     * are running, since these animations operate on layout-related properties.
     *
     * @return true if CHANGE_APPEARING or CHANGE_DISAPPEARING animations are currently
     * running.
     */
    public boolean isChangingLayout() {
        return (currentChangingAnimations.size() > 0);
    }

    
Returns true if any of the animations in this transition are currently running.

Returns:true if any animations in the transition are running.
/**
     * Returns true if any of the animations in this transition are currently running.
     *
     * @return true if any animations in the transition are running.
     */
    public boolean isRunning() {
        return (currentChangingAnimations.size() > 0 || currentAppearingAnimations.size() > 0 ||
                currentDisappearingAnimations.size() > 0);
    }

    
Cancels the currently running transition. Note that we cancel() the changing animations
but end() the visibility animations. This is because this method is currently called
in the context of starting a new transition, so we want to move things from their mid-
transition positions, but we want them to have their end-transition visibility.

@hide
/**
     * Cancels the currently running transition. Note that we cancel() the changing animations
     * but end() the visibility animations. This is because this method is currently called
     * in the context of starting a new transition, so we want to move things from their mid-
     * transition positions, but we want them to have their end-transition visibility.
     *
     * @hide
     */
    public void cancel() {
        if (currentChangingAnimations.size() > 0) {
            LinkedHashMap<View, Animator> currentAnimCopy =
                    (LinkedHashMap<View, Animator>) currentChangingAnimations.clone();
            for (Animator anim : currentAnimCopy.values()) {
                anim.cancel();
            }
            currentChangingAnimations.clear();
        }
        if (currentAppearingAnimations.size() > 0) {
            LinkedHashMap<View, Animator> currentAnimCopy =
                    (LinkedHashMap<View, Animator>) currentAppearingAnimations.clone();
            for (Animator anim : currentAnimCopy.values()) {
                anim.end();
            }
            currentAppearingAnimations.clear();
        }
        if (currentDisappearingAnimations.size() > 0) {
            LinkedHashMap<View, Animator> currentAnimCopy =
                    (LinkedHashMap<View, Animator>) currentDisappearingAnimations.clone();
            for (Animator anim : currentAnimCopy.values()) {
                anim.end();
            }
            currentDisappearingAnimations.clear();
        }
    }

    
Cancels the specified type of transition. Note that we cancel() the changing animations
but end() the visibility animations. This is because this method is currently called
in the context of starting a new transition, so we want to move things from their mid-
transition positions, but we want them to have their end-transition visibility.

@hide
/**
     * Cancels the specified type of transition. Note that we cancel() the changing animations
     * but end() the visibility animations. This is because this method is currently called
     * in the context of starting a new transition, so we want to move things from their mid-
     * transition positions, but we want them to have their end-transition visibility.
     *
     * @hide
     */
    public void cancel(int transitionType) {
        switch (transitionType) {
            case CHANGE_APPEARING:
            case CHANGE_DISAPPEARING:
            case CHANGING:
                if (currentChangingAnimations.size() > 0) {
                    LinkedHashMap<View, Animator> currentAnimCopy =
                            (LinkedHashMap<View, Animator>) currentChangingAnimations.clone();
                    for (Animator anim : currentAnimCopy.values()) {
                        anim.cancel();
                    }
                    currentChangingAnimations.clear();
                }
                break;
            case APPEARING:
                if (currentAppearingAnimations.size() > 0) {
                    LinkedHashMap<View, Animator> currentAnimCopy =
                            (LinkedHashMap<View, Animator>) currentAppearingAnimations.clone();
                    for (Animator anim : currentAnimCopy.values()) {
                        anim.end();
                    }
                    currentAppearingAnimations.clear();
                }
                break;
            case DISAPPEARING:
                if (currentDisappearingAnimations.size() > 0) {
                    LinkedHashMap<View, Animator> currentAnimCopy =
                            (LinkedHashMap<View, Animator>) currentDisappearingAnimations.clone();
                    for (Animator anim : currentAnimCopy.values()) {
                        anim.end();
                    }
                    currentDisappearingAnimations.clear();
                }
                break;
        }
    }

    
This method runs the animation that makes an added item appear.

Params:
  • parent – The ViewGroup to which the View is being added.
  • child – The View being added to the ViewGroup.
/**
     * This method runs the animation that makes an added item appear.
     *
     * @param parent The ViewGroup to which the View is being added.
     * @param child The View being added to the ViewGroup.
     */
    private void runAppearingTransition(final ViewGroup parent, final View child) {
        Animator currentAnimation = currentDisappearingAnimations.get(child);
        if (currentAnimation != null) {
            currentAnimation.cancel();
        }
        if (mAppearingAnim == null) {
            if (hasListeners()) {
                ArrayList<TransitionListener> listeners =
                        (ArrayList<TransitionListener>) mListeners.clone();
                for (TransitionListener listener : listeners) {
                    listener.endTransition(LayoutTransition.this, parent, child, APPEARING);
                }
            }
            return;
        }
        Animator anim = mAppearingAnim.clone();
        anim.setTarget(child);
        anim.setStartDelay(mAppearingDelay);
        anim.setDuration(mAppearingDuration);
        if (mAppearingInterpolator != sAppearingInterpolator) {
            anim.setInterpolator(mAppearingInterpolator);
        }
        if (anim instanceof ObjectAnimator) {
            ((ObjectAnimator) anim).setCurrentPlayTime(0);
        }
        anim.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator anim) {
                currentAppearingAnimations.remove(child);
                if (hasListeners()) {
                    ArrayList<TransitionListener> listeners =
                            (ArrayList<TransitionListener>) mListeners.clone();
                    for (TransitionListener listener : listeners) {
                        listener.endTransition(LayoutTransition.this, parent, child, APPEARING);
                    }
                }
            }
        });
        currentAppearingAnimations.put(child, anim);
        anim.start();
    }

    
This method runs the animation that makes a removed item disappear.

Params:
  • parent – The ViewGroup from which the View is being removed.
  • child – The View being removed from the ViewGroup.
/**
     * This method runs the animation that makes a removed item disappear.
     *
     * @param parent The ViewGroup from which the View is being removed.
     * @param child The View being removed from the ViewGroup.
     */
    private void runDisappearingTransition(final ViewGroup parent, final View child) {
        Animator currentAnimation = currentAppearingAnimations.get(child);
        if (currentAnimation != null) {
            currentAnimation.cancel();
        }
        if (mDisappearingAnim == null) {
            if (hasListeners()) {
                ArrayList<TransitionListener> listeners =
                        (ArrayList<TransitionListener>) mListeners.clone();
                for (TransitionListener listener : listeners) {
                    listener.endTransition(LayoutTransition.this, parent, child, DISAPPEARING);
                }
            }
            return;
        }
        Animator anim = mDisappearingAnim.clone();
        anim.setStartDelay(mDisappearingDelay);
        anim.setDuration(mDisappearingDuration);
        if (mDisappearingInterpolator != sDisappearingInterpolator) {
            anim.setInterpolator(mDisappearingInterpolator);
        }
        anim.setTarget(child);
        final float preAnimAlpha = child.getAlpha();
        anim.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator anim) {
                currentDisappearingAnimations.remove(child);
                child.setAlpha(preAnimAlpha);
                if (hasListeners()) {
                    ArrayList<TransitionListener> listeners =
                            (ArrayList<TransitionListener>) mListeners.clone();
                    for (TransitionListener listener : listeners) {
                        listener.endTransition(LayoutTransition.this, parent, child, DISAPPEARING);
                    }
                }
            }
        });
        if (anim instanceof ObjectAnimator) {
            ((ObjectAnimator) anim).setCurrentPlayTime(0);
        }
        currentDisappearingAnimations.put(child, anim);
        anim.start();
    }

    
This method is called by ViewGroup when a child view is about to be added to the
container. This callback starts the process of a transition; we grab the starting
values, listen for changes to all of the children of the container, and start appropriate
animations.

Params:
  • parent – The ViewGroup to which the View is being added.
  • child – The View being added to the ViewGroup.
  • changesLayout – Whether the removal will cause changes in the layout of other views
in the container. INVISIBLE views becoming VISIBLE will not cause changes and thus will not
affect CHANGE_APPEARING or CHANGE_DISAPPEARING animations.
/**
     * This method is called by ViewGroup when a child view is about to be added to the
     * container. This callback starts the process of a transition; we grab the starting
     * values, listen for changes to all of the children of the container, and start appropriate
     * animations.
     *
     * @param parent The ViewGroup to which the View is being added.
     * @param child The View being added to the ViewGroup.
     * @param changesLayout Whether the removal will cause changes in the layout of other views
     * in the container. INVISIBLE views becoming VISIBLE will not cause changes and thus will not
     * affect CHANGE_APPEARING or CHANGE_DISAPPEARING animations.
     */
    private void addChild(ViewGroup parent, View child, boolean changesLayout) {
        if (parent.getWindowVisibility() != View.VISIBLE) {
            return;
        }
        if ((mTransitionTypes & FLAG_APPEARING) == FLAG_APPEARING) {
            // Want disappearing animations to finish up before proceeding
            cancel(DISAPPEARING);
        }
        if (changesLayout && (mTransitionTypes & FLAG_CHANGE_APPEARING) == FLAG_CHANGE_APPEARING) {
            // Also, cancel changing animations so that we start fresh ones from current locations
            cancel(CHANGE_APPEARING);
            cancel(CHANGING);
        }
        if (hasListeners() && (mTransitionTypes & FLAG_APPEARING) == FLAG_APPEARING) {
            ArrayList<TransitionListener> listeners =
                    (ArrayList<TransitionListener>) mListeners.clone();
            for (TransitionListener listener : listeners) {
                listener.startTransition(this, parent, child, APPEARING);
            }
        }
        if (changesLayout && (mTransitionTypes & FLAG_CHANGE_APPEARING) == FLAG_CHANGE_APPEARING) {
            runChangeTransition(parent, child, APPEARING);
        }
        if ((mTransitionTypes & FLAG_APPEARING) == FLAG_APPEARING) {
            runAppearingTransition(parent, child);
        }
    }

    private boolean hasListeners() {
        return mListeners != null && mListeners.size() > 0;
    }

    
This method is called by ViewGroup when there is a call to layout() on the container
with this LayoutTransition. If the CHANGING transition is enabled and if there is no other
transition currently running on the container, then this call runs a CHANGING transition.
The transition does not start immediately; it just sets up the mechanism to run if any
of the children of the container change their layout parameters (similar to
the CHANGE_APPEARING and CHANGE_DISAPPEARING transitions).

Params:
  • parent – The ViewGroup whose layout() method has been called.
@hide
/**
     * This method is called by ViewGroup when there is a call to layout() on the container
     * with this LayoutTransition. If the CHANGING transition is enabled and if there is no other
     * transition currently running on the container, then this call runs a CHANGING transition.
     * The transition does not start immediately; it just sets up the mechanism to run if any
     * of the children of the container change their layout parameters (similar to
     * the CHANGE_APPEARING and CHANGE_DISAPPEARING transitions).
     *
     * @param parent The ViewGroup whose layout() method has been called.
     *
     * @hide
     */
    public void layoutChange(ViewGroup parent) {
        if (parent.getWindowVisibility() != View.VISIBLE) {
            return;
        }
        if ((mTransitionTypes & FLAG_CHANGING) == FLAG_CHANGING  && !isRunning()) {
            // This method is called for all calls to layout() in the container, including
            // those caused by add/remove/hide/show events, which will already have set up
            // transition animations. Avoid setting up CHANGING animations in this case; only
            // do so when there is not a transition already running on the container.
            runChangeTransition(parent, null, CHANGING);
        }
    }

    
This method is called by ViewGroup when a child view is about to be added to the
container. This callback starts the process of a transition; we grab the starting
values, listen for changes to all of the children of the container, and start appropriate
animations.

Params:
  • parent – The ViewGroup to which the View is being added.
  • child – The View being added to the ViewGroup.
/**
     * This method is called by ViewGroup when a child view is about to be added to the
     * container. This callback starts the process of a transition; we grab the starting
     * values, listen for changes to all of the children of the container, and start appropriate
     * animations.
     *
     * @param parent The ViewGroup to which the View is being added.
     * @param child The View being added to the ViewGroup.
     */
    public void addChild(ViewGroup parent, View child) {
        addChild(parent, child, true);
    }

    
Deprecated:Use showChild(ViewGroup, View, int).
/**
     * @deprecated Use {@link #showChild(android.view.ViewGroup, android.view.View, int)}.
     */
    @Deprecated
    public void showChild(ViewGroup parent, View child) {
        addChild(parent, child, true);
    }

    
This method is called by ViewGroup when a child view is about to be made visible in the
container. This callback starts the process of a transition; we grab the starting
values, listen for changes to all of the children of the container, and start appropriate
animations.

Params:
  • parent – The ViewGroup in which the View is being made visible.
  • child – The View being made visible.
  • oldVisibility – The previous visibility value of the child View, either View.GONE or View.INVISIBLE.
/**
     * This method is called by ViewGroup when a child view is about to be made visible in the
     * container. This callback starts the process of a transition; we grab the starting
     * values, listen for changes to all of the children of the container, and start appropriate
     * animations.
     *
     * @param parent The ViewGroup in which the View is being made visible.
     * @param child The View being made visible.
     * @param oldVisibility The previous visibility value of the child View, either
     * {@link View#GONE} or {@link View#INVISIBLE}.
     */
    public void showChild(ViewGroup parent, View child, int oldVisibility) {
        addChild(parent, child, oldVisibility == View.GONE);
    }

    
This method is called by ViewGroup when a child view is about to be removed from the
container. This callback starts the process of a transition; we grab the starting
values, listen for changes to all of the children of the container, and start appropriate
animations.

Params:
  • parent – The ViewGroup from which the View is being removed.
  • child – The View being removed from the ViewGroup.
  • changesLayout – Whether the removal will cause changes in the layout of other views
in the container. Views becoming INVISIBLE will not cause changes and thus will not
affect CHANGE_APPEARING or CHANGE_DISAPPEARING animations.
/**
     * This method is called by ViewGroup when a child view is about to be removed from the
     * container. This callback starts the process of a transition; we grab the starting
     * values, listen for changes to all of the children of the container, and start appropriate
     * animations.
     *
     * @param parent The ViewGroup from which the View is being removed.
     * @param child The View being removed from the ViewGroup.
     * @param changesLayout Whether the removal will cause changes in the layout of other views
     * in the container. Views becoming INVISIBLE will not cause changes and thus will not
     * affect CHANGE_APPEARING or CHANGE_DISAPPEARING animations.
     */
    private void removeChild(ViewGroup parent, View child, boolean changesLayout) {
        if (parent.getWindowVisibility() != View.VISIBLE) {
            return;
        }
        if ((mTransitionTypes & FLAG_DISAPPEARING) == FLAG_DISAPPEARING) {
            // Want appearing animations to finish up before proceeding
            cancel(APPEARING);
        }
        if (changesLayout &&
                (mTransitionTypes & FLAG_CHANGE_DISAPPEARING) == FLAG_CHANGE_DISAPPEARING) {
            // Also, cancel changing animations so that we start fresh ones from current locations
            cancel(CHANGE_DISAPPEARING);
            cancel(CHANGING);
        }
        if (hasListeners() && (mTransitionTypes & FLAG_DISAPPEARING) == FLAG_DISAPPEARING) {
            ArrayList<TransitionListener> listeners = (ArrayList<TransitionListener>) mListeners
                    .clone();
            for (TransitionListener listener : listeners) {
                listener.startTransition(this, parent, child, DISAPPEARING);
            }
        }
        if (changesLayout &&
                (mTransitionTypes & FLAG_CHANGE_DISAPPEARING) == FLAG_CHANGE_DISAPPEARING) {
            runChangeTransition(parent, child, DISAPPEARING);
        }
        if ((mTransitionTypes & FLAG_DISAPPEARING) == FLAG_DISAPPEARING) {
            runDisappearingTransition(parent, child);
        }
    }

    
This method is called by ViewGroup when a child view is about to be removed from the
container. This callback starts the process of a transition; we grab the starting
values, listen for changes to all of the children of the container, and start appropriate
animations.

Params:
  • parent – The ViewGroup from which the View is being removed.
  • child – The View being removed from the ViewGroup.
/**
     * This method is called by ViewGroup when a child view is about to be removed from the
     * container. This callback starts the process of a transition; we grab the starting
     * values, listen for changes to all of the children of the container, and start appropriate
     * animations.
     *
     * @param parent The ViewGroup from which the View is being removed.
     * @param child The View being removed from the ViewGroup.
     */
    public void removeChild(ViewGroup parent, View child) {
        removeChild(parent, child, true);
    }

    
Deprecated:Use hideChild(ViewGroup, View, int).
/**
     * @deprecated Use {@link #hideChild(android.view.ViewGroup, android.view.View, int)}.
     */
    @Deprecated
    public void hideChild(ViewGroup parent, View child) {
        removeChild(parent, child, true);
    }

    
This method is called by ViewGroup when a child view is about to be hidden in
container. This callback starts the process of a transition; we grab the starting
values, listen for changes to all of the children of the container, and start appropriate
animations.

Params:
  • parent – The parent ViewGroup of the View being hidden.
  • child – The View being hidden.
  • newVisibility – The new visibility value of the child View, either View.GONE or View.INVISIBLE.
/**
     * This method is called by ViewGroup when a child view is about to be hidden in
     * container. This callback starts the process of a transition; we grab the starting
     * values, listen for changes to all of the children of the container, and start appropriate
     * animations.
     *
     * @param parent The parent ViewGroup of the View being hidden.
     * @param child The View being hidden.
     * @param newVisibility The new visibility value of the child View, either
     * {@link View#GONE} or {@link View#INVISIBLE}.
     */
    public void hideChild(ViewGroup parent, View child, int newVisibility) {
        removeChild(parent, child, newVisibility == View.GONE);
    }

    
Add a listener that will be called when the bounds of the view change due to
layout processing.

Params:
  • listener – The listener that will be called when layout bounds change.
/**
     * Add a listener that will be called when the bounds of the view change due to
     * layout processing.
     *
     * @param listener The listener that will be called when layout bounds change.
     */
    public void addTransitionListener(TransitionListener listener) {
        if (mListeners == null) {
            mListeners = new ArrayList<TransitionListener>();
        }
        mListeners.add(listener);
    }

    
Remove a listener for layout changes.

Params:
  • listener – The listener for layout bounds change.
/**
     * Remove a listener for layout changes.
     *
     * @param listener The listener for layout bounds change.
     */
    public void removeTransitionListener(TransitionListener listener) {
        if (mListeners == null) {
            return;
        }
        mListeners.remove(listener);
    }

    
Gets the current list of listeners for layout changes.

Returns:
/**
     * Gets the current list of listeners for layout changes.
     * @return
     */
    public List<TransitionListener> getTransitionListeners() {
        return mListeners;
    }

    
This interface is used for listening to starting and ending events for transitions.

/**
     * This interface is used for listening to starting and ending events for transitions.
     */
    public interface TransitionListener {

        
This event is sent to listeners when any type of transition animation begins.

Params:
/**
         * This event is sent to listeners when any type of transition animation begins.
         *
         * @param transition The LayoutTransition sending out the event.
         * @param container The ViewGroup on which the transition is playing.
         * @param view The View object being affected by the transition animation.
         * @param transitionType The type of transition that is beginning,
         * {@link android.animation.LayoutTransition#APPEARING},
         * {@link android.animation.LayoutTransition#DISAPPEARING},
         * {@link android.animation.LayoutTransition#CHANGE_APPEARING}, or
         * {@link android.animation.LayoutTransition#CHANGE_DISAPPEARING}.
         */
        public void startTransition(LayoutTransition transition, ViewGroup container,
                View view, int transitionType);

        
This event is sent to listeners when any type of transition animation ends.

Params:
/**
         * This event is sent to listeners when any type of transition animation ends.
         *
         * @param transition The LayoutTransition sending out the event.
         * @param container The ViewGroup on which the transition is playing.
         * @param view The View object being affected by the transition animation.
         * @param transitionType The type of transition that is ending,
         * {@link android.animation.LayoutTransition#APPEARING},
         * {@link android.animation.LayoutTransition#DISAPPEARING},
         * {@link android.animation.LayoutTransition#CHANGE_APPEARING}, or
         * {@link android.animation.LayoutTransition#CHANGE_DISAPPEARING}.
         */
        public void endTransition(LayoutTransition transition, ViewGroup container,
                View view, int transitionType);
    }

    
Utility class to clean up listeners after animations are setup. Cleanup happens
when either the OnPreDrawListener method is called or when the parent is detached,
whichever comes first.

/**
     * Utility class to clean up listeners after animations are setup. Cleanup happens
     * when either the OnPreDrawListener method is called or when the parent is detached,
     * whichever comes first.
     */
    private static final class CleanupCallback implements ViewTreeObserver.OnPreDrawListener,
            View.OnAttachStateChangeListener {

        final Map<View, View.OnLayoutChangeListener> layoutChangeListenerMap;
        final ViewGroup parent;

        CleanupCallback(Map<View, View.OnLayoutChangeListener> listenerMap, ViewGroup parent) {
            this.layoutChangeListenerMap = listenerMap;
            this.parent = parent;
        }

        private void cleanup() {
            parent.getViewTreeObserver().removeOnPreDrawListener(this);
            parent.removeOnAttachStateChangeListener(this);
            int count = layoutChangeListenerMap.size();
            if (count > 0) {
                Collection<View> views = layoutChangeListenerMap.keySet();
                for (View view : views) {
                    View.OnLayoutChangeListener listener = layoutChangeListenerMap.get(view);
                    view.removeOnLayoutChangeListener(listener);
                }
                layoutChangeListenerMap.clear();
            }
        }

        @Override
        public void onViewAttachedToWindow(View v) {
        }

        @Override
        public void onViewDetachedFromWindow(View v) {
            cleanup();
        }

        @Override
        public boolean onPreDraw() {
            cleanup();
            return true;
        }
    };

}