public abstract class

FragmentTransitionImpl

extends java.lang.Object

 java.lang.Object

↳androidx.fragment.app.FragmentTransitionImpl

Subclasses:

FragmentTransitionSupport

Gradle dependencies

compile group: 'androidx.fragment', name: 'fragment', version: '1.8.3'

  • groupId: androidx.fragment
  • artifactId: fragment
  • version: 1.8.3

Artifact androidx.fragment:fragment:1.8.3 it located at Google repository (https://maven.google.com/)

Androidx artifact mapping:

androidx.fragment:fragment com.android.support:support-fragment

Androidx class mapping:

androidx.fragment.app.FragmentTransitionImpl android.support.v4.app.FragmentTransitionImpl

Summary

Constructors
publicFragmentTransitionImpl()

Methods
public abstract voidaddTarget(java.lang.Object transitionObj, View view)

Adds a View target to a transition.

public abstract voidaddTargets(java.lang.Object transitionObj, java.util.ArrayList<View> views)

This method adds views as targets to the transition, but only if the transition doesn't already have a target.

public voidanimateToEnd(java.lang.Object transitionController)

Animate the transition to end.

public voidanimateToStart(java.lang.Object transitionController, java.lang.Runnable completeRunnable)

Animate the transition to start.

public abstract voidbeginDelayedTransition(ViewGroup sceneRoot, java.lang.Object transition)

Calls TransitionManager#beginDelayedTransition(ViewGroup, Transition).

protected static voidbfsAddViewChildren(java.util.List<View> views, View startView)

Uses a breadth-first scheme to add startView and all of its children to views.

public abstract booleancanHandle(java.lang.Object transition)

Returns true if this implementation can handle the specified .

public abstract java.lang.ObjectcloneTransition(java.lang.Object transition)

Returns a clone of a transition or null if it is null

public java.lang.ObjectcontrolDelayedTransition(ViewGroup sceneRoot, java.lang.Object transition)

Allows for controlling a seekable transition

protected voidgetBoundsOnScreen(View view, Rect epicenter)

Replacement for view.getBoundsOnScreen because that is not public.

protected static booleanisNullOrEmpty(java.util.List list)

Simple utility to detect if a list is null or has no elements.

public booleanisSeekingSupported()

Returns true if the Transition is seekable.

public booleanisSeekingSupported(java.lang.Object transition)

Returns true if the Transition is seekable.

public abstract java.lang.ObjectmergeTransitionsInSequence(java.lang.Object exitTransitionObj, java.lang.Object enterTransitionObj, java.lang.Object sharedElementTransitionObj)

Combines enter, exit, and shared element transition so that they play in the proper sequence.

public abstract java.lang.ObjectmergeTransitionsTogether(java.lang.Object transition1, java.lang.Object transition2, java.lang.Object transition3)

Creates a TransitionSet that plays all passed transitions together.

public abstract voidremoveTarget(java.lang.Object transitionObj, View view)

Remove a View target to a transition.

public abstract voidreplaceTargets(java.lang.Object transitionObj, java.util.ArrayList<View> oldTargets, java.util.ArrayList<View> newTargets)

This method removes the views from transitions that target ONLY those views and replaces them with the new targets list.

public abstract voidscheduleHideFragmentView(java.lang.Object exitTransitionObj, View fragmentView, java.util.ArrayList<View> exitingViews)

After the transition completes, the fragment's view is set to GONE and the exiting views are set to VISIBLE.

public abstract voidscheduleRemoveTargets(java.lang.Object overallTransitionObj, java.lang.Object enterTransition, java.util.ArrayList<View> enteringViews, java.lang.Object exitTransition, java.util.ArrayList<View> exitingViews, java.lang.Object sharedElementTransition, java.util.ArrayList<View> sharedElementsIn)

After the transition has started, remove all targets that we added to the transitions so that the transitions are left in a clean state.

public voidsetCurrentPlayTime(java.lang.Object transitionController, float progress)

Uses given progress to set the current play time of the transition.

public abstract voidsetEpicenter(java.lang.Object transitionObj, Rect epicenter)

Sets the epicenter of a transition to a rect object.

public abstract voidsetEpicenter(java.lang.Object transitionObj, View view)

Sets a transition epicenter to the rectangle of a given View.

public voidsetListenerForTransitionEnd(Fragment outFragment, java.lang.Object transition, CancellationSignal signal, java.lang.Runnable transitionCompleteRunnable)

Set a listener for Transition end events.

public voidsetListenerForTransitionEnd(Fragment outFragment, java.lang.Object transition, CancellationSignal signal, java.lang.Runnable cancelRunnable, java.lang.Runnable transitionCompleteRunnable)

Set a listener for Transition end events.

public abstract voidsetSharedElementTargets(java.lang.Object transitionObj, View nonExistentView, java.util.ArrayList<View> sharedViews)

Finds all children of the shared elements and sets the wrapping TransitionSet targets to point to those.

public abstract voidswapSharedElementTargets(java.lang.Object sharedElementTransitionObj, java.util.ArrayList<View> sharedElementsOut, java.util.ArrayList<View> sharedElementsIn)

Swap the targets for the shared element transition from those Views in sharedElementsOut to those in sharedElementsIn

public abstract java.lang.ObjectwrapTransitionInSet(java.lang.Object transition)

Wraps a transition in a TransitionSet and returns the set.

from java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructors

public FragmentTransitionImpl()

Methods

public abstract boolean canHandle(java.lang.Object transition)

Returns true if this implementation can handle the specified .

public abstract java.lang.Object cloneTransition(java.lang.Object transition)

Returns a clone of a transition or null if it is null

public abstract java.lang.Object wrapTransitionInSet(java.lang.Object transition)

Wraps a transition in a TransitionSet and returns the set. If transition is null, null is returned.

public abstract void setSharedElementTargets(java.lang.Object transitionObj, View nonExistentView, java.util.ArrayList<View> sharedViews)

Finds all children of the shared elements and sets the wrapping TransitionSet targets to point to those. It also limits transitions that have no targets to the specific shared elements. This allows developers to target child views of the shared elements specifically, but this doesn't happen by default.

public abstract void setEpicenter(java.lang.Object transitionObj, View view)

Sets a transition epicenter to the rectangle of a given View.

protected void getBoundsOnScreen(View view, Rect epicenter)

Replacement for view.getBoundsOnScreen because that is not public. This returns a rect containing the bounds relative to the screen that the view is in.

public abstract void addTargets(java.lang.Object transitionObj, java.util.ArrayList<View> views)

This method adds views as targets to the transition, but only if the transition doesn't already have a target. It is best for views to contain one View object that does not exist in the view hierarchy (state.nonExistentView) so that when they are removed later, a list match will suffice to remove the targets. Otherwise, if you happened to have targeted the exact views for the transition, the replaceTargets call will remove them unexpectedly.

public abstract java.lang.Object mergeTransitionsTogether(java.lang.Object transition1, java.lang.Object transition2, java.lang.Object transition3)

Creates a TransitionSet that plays all passed transitions together. Any null transitions passed will not be added to the set. If all are null, then an empty TransitionSet will be returned.

public abstract void scheduleHideFragmentView(java.lang.Object exitTransitionObj, View fragmentView, java.util.ArrayList<View> exitingViews)

After the transition completes, the fragment's view is set to GONE and the exiting views are set to VISIBLE.

public abstract java.lang.Object mergeTransitionsInSequence(java.lang.Object exitTransitionObj, java.lang.Object enterTransitionObj, java.lang.Object sharedElementTransitionObj)

Combines enter, exit, and shared element transition so that they play in the proper sequence. First the exit transition plays along with the shared element transition. When the exit transition completes, the enter transition starts. The shared element transition can continue running while the enter transition plays.

Returns:

A TransitionSet with all of enter, exit, and shared element transitions in it (modulo null values), ordered such that they play in the proper sequence.

public abstract void beginDelayedTransition(ViewGroup sceneRoot, java.lang.Object transition)

Calls TransitionManager#beginDelayedTransition(ViewGroup, Transition).

public boolean isSeekingSupported()

Returns true if the Transition is seekable.

public boolean isSeekingSupported(java.lang.Object transition)

Returns true if the Transition is seekable.

public java.lang.Object controlDelayedTransition(ViewGroup sceneRoot, java.lang.Object transition)

Allows for controlling a seekable transition

public void setCurrentPlayTime(java.lang.Object transitionController, float progress)

Uses given progress to set the current play time of the transition.

public void animateToEnd(java.lang.Object transitionController)

Animate the transition to end.

public void animateToStart(java.lang.Object transitionController, java.lang.Runnable completeRunnable)

Animate the transition to start.

public abstract void scheduleRemoveTargets(java.lang.Object overallTransitionObj, java.lang.Object enterTransition, java.util.ArrayList<View> enteringViews, java.lang.Object exitTransition, java.util.ArrayList<View> exitingViews, java.lang.Object sharedElementTransition, java.util.ArrayList<View> sharedElementsIn)

After the transition has started, remove all targets that we added to the transitions so that the transitions are left in a clean state.

public void setListenerForTransitionEnd(Fragment outFragment, java.lang.Object transition, CancellationSignal signal, java.lang.Runnable transitionCompleteRunnable)

Set a listener for Transition end events. The default behavior immediately completes the transition.

Parameters:

outFragment: The first fragment that is exiting
transition: all transitions to be executed on a single container
signal: used indicate the desired behavior on transition cancellation
transitionCompleteRunnable: used to notify the FragmentManager when a transition is complete

public void setListenerForTransitionEnd(Fragment outFragment, java.lang.Object transition, CancellationSignal signal, java.lang.Runnable cancelRunnable, java.lang.Runnable transitionCompleteRunnable)

Set a listener for Transition end events. The default behavior immediately completes the transition. Use this when the given transition is seeking. The cancelRunnable should handle cleaning up the transition when seeking is cancelled. If the transition is not seeking, you should use FragmentTransitionImpl.setListenerForTransitionEnd(Fragment, Object, CancellationSignal, Runnable).

Parameters:

outFragment: The first fragment that is exiting
transition: all transitions to be executed on a single container
signal: used indicate the desired behavior on transition cancellation
cancelRunnable: runnable to handle the logic when the signal is cancelled
transitionCompleteRunnable: used to notify the FragmentManager when a transition is complete

public abstract void swapSharedElementTargets(java.lang.Object sharedElementTransitionObj, java.util.ArrayList<View> sharedElementsOut, java.util.ArrayList<View> sharedElementsIn)

Swap the targets for the shared element transition from those Views in sharedElementsOut to those in sharedElementsIn

public abstract void replaceTargets(java.lang.Object transitionObj, java.util.ArrayList<View> oldTargets, java.util.ArrayList<View> newTargets)

This method removes the views from transitions that target ONLY those views and replaces them with the new targets list. The views list should match those added in addTargets and should contain one view that is not in the view hierarchy (state.nonExistentView).

public abstract void addTarget(java.lang.Object transitionObj, View view)

Adds a View target to a transition. If transitionObj is null, nothing is done.

public abstract void removeTarget(java.lang.Object transitionObj, View view)

Remove a View target to a transition. If transitionObj is null, nothing is done.

public abstract void setEpicenter(java.lang.Object transitionObj, Rect epicenter)

Sets the epicenter of a transition to a rect object. The object can be modified until the transition runs.

protected static void bfsAddViewChildren(java.util.List<View> views, View startView)

Uses a breadth-first scheme to add startView and all of its children to views. It won't add a child if it is already in views or if it has a transition name.

protected static boolean isNullOrEmpty(java.util.List list)

Simple utility to detect if a list is null or has no elements.

Source

/*
 * Copyright 2018 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 androidx.fragment.app;

import static androidx.annotation.RestrictTo.Scope.LIBRARY_GROUP_PREFIX;

import android.annotation.SuppressLint;
import android.graphics.Rect;
import android.graphics.RectF;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.annotation.RestrictTo;
import androidx.core.view.OneShotPreDrawListener;
import androidx.core.view.ViewCompat;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;


/**
 */
@RestrictTo(LIBRARY_GROUP_PREFIX)
@SuppressLint("UnknownNullness")
public abstract class FragmentTransitionImpl {

    /**
     * Returns {@code true} if this implementation can handle the specified {@link transition}.
     */
    public abstract boolean canHandle(@NonNull Object transition);

    /**
     * Returns a clone of a transition or null if it is null
     */
    public abstract Object cloneTransition(@Nullable Object transition);

    /**
     * Wraps a transition in a TransitionSet and returns the set. If transition is null, null is
     * returned.
     */
    public abstract Object wrapTransitionInSet(@Nullable Object transition);

    /**
     * Finds all children of the shared elements and sets the wrapping TransitionSet
     * targets to point to those. It also limits transitions that have no targets to the
     * specific shared elements. This allows developers to target child views of the
     * shared elements specifically, but this doesn't happen by default.
     */
    public abstract void setSharedElementTargets(@NonNull Object transitionObj,
            @NonNull View nonExistentView, @NonNull ArrayList<View> sharedViews);

    /**
     * Sets a transition epicenter to the rectangle of a given View.
     */
    public abstract void setEpicenter(@NonNull Object transitionObj, @Nullable View view);

    /**
     * Replacement for view.getBoundsOnScreen because that is not public. This returns a rect
     * containing the bounds relative to the screen that the view is in.
     */
    protected void getBoundsOnScreen(View view, Rect epicenter) {
        if (!view.isAttachedToWindow()) {
            return;
        }

        final RectF rect = new RectF();
        rect.set(0, 0, view.getWidth(), view.getHeight());

        view.getMatrix().mapRect(rect);
        rect.offset(view.getLeft(), view.getTop());

        ViewParent parent = view.getParent();
        while (parent instanceof View) {
            View parentView = (View) parent;

            rect.offset(-parentView.getScrollX(), -parentView.getScrollY());
            parentView.getMatrix().mapRect(rect);
            rect.offset(parentView.getLeft(), parentView.getTop());

            parent = parentView.getParent();
        }

        final int[] loc = new int[2];
        view.getRootView().getLocationOnScreen(loc);
        rect.offset(loc[0], loc[1]);
        epicenter.set(Math.round(rect.left), Math.round(rect.top), Math.round(rect.right),
                Math.round(rect.bottom));
    }

    /**
     * This method adds views as targets to the transition, but only if the transition
     * doesn't already have a target. It is best for views to contain one View object
     * that does not exist in the view hierarchy (state.nonExistentView) so that
     * when they are removed later, a list match will suffice to remove the targets.
     * Otherwise, if you happened to have targeted the exact views for the transition,
     * the replaceTargets call will remove them unexpectedly.
     */
    public abstract void addTargets(@NonNull Object transitionObj, @NonNull ArrayList<View> views);

    /**
     * Creates a TransitionSet that plays all passed transitions together. Any null
     * transitions passed will not be added to the set. If all are null, then an empty
     * TransitionSet will be returned.
     */
    public abstract Object mergeTransitionsTogether(@Nullable Object transition1,
            @Nullable Object transition2, @Nullable Object transition3);

    /**
     * After the transition completes, the fragment's view is set to GONE and the exiting
     * views are set to VISIBLE.
     */
    public abstract void scheduleHideFragmentView(@NonNull Object exitTransitionObj,
            @NonNull View fragmentView, @NonNull ArrayList<View> exitingViews);

    /**
     * Combines enter, exit, and shared element transition so that they play in the proper
     * sequence. First the exit transition plays along with the shared element transition.
     * When the exit transition completes, the enter transition starts. The shared element
     * transition can continue running while the enter transition plays.
     *
     * @return A TransitionSet with all of enter, exit, and shared element transitions in
     * it (modulo null values), ordered such that they play in the proper sequence.
     */
    public abstract Object mergeTransitionsInSequence(@Nullable Object exitTransitionObj,
            @Nullable Object enterTransitionObj, @Nullable Object sharedElementTransitionObj);

    /**
     * Calls {@code TransitionManager#beginDelayedTransition(ViewGroup, Transition)}.
     */
    public abstract void beginDelayedTransition(@NonNull ViewGroup sceneRoot,
            @Nullable Object transition);

    /**
     * Returns {@code true} if the Transition is seekable.
     */
    public boolean isSeekingSupported() {
        if (FragmentManager.isLoggingEnabled(Log.INFO)) {
            Log.i(FragmentManager.TAG,
                    "Older versions of AndroidX Transition do not support seeking. Add dependency "
                            + "on AndroidX Transition 1.5.0 or higher to enable seeking.");
        }
        return false;
    }

    /**
     * Returns {@code true} if the Transition is seekable.
     */
    public boolean isSeekingSupported(@NonNull Object transition) {
        return false;
    }

    /**
     * Allows for controlling a seekable transition
     */
    @Nullable
    public Object controlDelayedTransition(@NonNull ViewGroup sceneRoot,
            @NonNull Object transition) {
        return null;
    }

    /**
     * Uses given progress to set the current play time of the transition.
     */
    public void setCurrentPlayTime(@NonNull Object transitionController, float progress) { }

    /**
     * Animate the transition to end.
     */
    public void animateToEnd(@NonNull Object transitionController) { }

    /**
     * Animate the transition to start.
     */
    public void animateToStart(
            @NonNull Object transitionController,
            @NonNull Runnable completeRunnable) {
    }

    /**
     * Prepares for setting the shared element names by gathering the names of the incoming
     * shared elements and clearing them. {@link #setNameOverridesReordered(View, ArrayList,
     * ArrayList, ArrayList, Map)} must be called after this to complete setting the shared element
     * name overrides. This must be called before
     * {@link #beginDelayedTransition(ViewGroup, Object)}.
     */
    ArrayList<String> prepareSetNameOverridesReordered(ArrayList<View> sharedElementsIn) {
        final ArrayList<String> names = new ArrayList<>();
        final int numSharedElements = sharedElementsIn.size();
        for (int i = 0; i < numSharedElements; i++) {
            final View view = sharedElementsIn.get(i);
            names.add(ViewCompat.getTransitionName(view));
            ViewCompat.setTransitionName(view, null);
        }
        return names;
    }

    /**
     * Changes the shared element names for the incoming shared elements to match those of the
     * outgoing shared elements. This also temporarily clears the shared element names of the
     * outgoing shared elements. Must be called after
     * {@link #beginDelayedTransition(ViewGroup, Object)}.
     */
    void setNameOverridesReordered(final View sceneRoot,
            final ArrayList<View> sharedElementsOut, final ArrayList<View> sharedElementsIn,
            final ArrayList<String> inNames, final Map<String, String> nameOverrides) {
        final int numSharedElements = sharedElementsIn.size();
        final ArrayList<String> outNames = new ArrayList<>();

        for (int i = 0; i < numSharedElements; i++) {
            final View view = sharedElementsOut.get(i);
            final String name = ViewCompat.getTransitionName(view);
            outNames.add(name);
            if (name == null) {
                continue;
            }
            ViewCompat.setTransitionName(view, null);
            final String inName = nameOverrides.get(name);
            for (int j = 0; j < numSharedElements; j++) {
                if (inName.equals(inNames.get(j))) {
                    ViewCompat.setTransitionName(sharedElementsIn.get(j), name);
                    break;
                }
            }
        }

        OneShotPreDrawListener.add(sceneRoot, new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < numSharedElements; i++) {
                    ViewCompat.setTransitionName(sharedElementsIn.get(i), inNames.get(i));
                    ViewCompat.setTransitionName(sharedElementsOut.get(i), outNames.get(i));
                }
            }
        });
    }

    /**
     * After the transition has started, remove all targets that we added to the transitions
     * so that the transitions are left in a clean state.
     */
    public abstract void scheduleRemoveTargets(@NonNull Object overallTransitionObj,
            @Nullable Object enterTransition, @Nullable ArrayList<View> enteringViews,
            @Nullable Object exitTransition, @Nullable ArrayList<View> exitingViews,
            @Nullable Object sharedElementTransition, @Nullable ArrayList<View> sharedElementsIn);


    /**
     * Set a listener for Transition end events. The default behavior immediately completes the
     * transition.
     *
     * @param outFragment The first fragment that is exiting
     * @param transition all transitions to be executed on a single container
     * @param signal used indicate the desired behavior on transition cancellation
     * @param transitionCompleteRunnable used to notify the FragmentManager when a transition is
     *                                   complete
     */
    @SuppressWarnings("deprecation") // TODO(b/309499026): Migrate to platform-provided class.
    public void setListenerForTransitionEnd(@NonNull final Fragment outFragment,
            @NonNull Object transition, @NonNull androidx.core.os.CancellationSignal signal,
            @NonNull Runnable transitionCompleteRunnable) {
        setListenerForTransitionEnd(
                outFragment, transition, signal, null, transitionCompleteRunnable
        );
    }

    /**
     * Set a listener for Transition end events. The default behavior immediately completes the
     * transition.
     *
     * Use this when the given transition is seeking. The cancelRunnable should handle
     * cleaning up the transition when seeking is cancelled.
     *
     * If the transition is not seeking, you should use
     * {@link #setListenerForTransitionEnd(Fragment, Object, androidx.core.os.CancellationSignal, Runnable)}.
     *
     * @param outFragment The first fragment that is exiting
     * @param transition all transitions to be executed on a single container
     * @param signal used indicate the desired behavior on transition cancellation
     * @param cancelRunnable runnable to handle the logic when the signal is cancelled
     * @param transitionCompleteRunnable used to notify the FragmentManager when a transition is
     *                                   complete
     */
    @SuppressWarnings("deprecation")
    public void setListenerForTransitionEnd(@NonNull final Fragment outFragment,
            @NonNull Object transition, @NonNull androidx.core.os.CancellationSignal signal,
            @Nullable Runnable cancelRunnable,
            @NonNull Runnable transitionCompleteRunnable) {
        transitionCompleteRunnable.run();
    }

    /**
     * Swap the targets for the shared element transition from those Views in sharedElementsOut
     * to those in sharedElementsIn
     */
    public abstract void swapSharedElementTargets(@Nullable Object sharedElementTransitionObj,
            @Nullable ArrayList<View> sharedElementsOut,
            @Nullable ArrayList<View> sharedElementsIn);

    /**
     * This method removes the views from transitions that target ONLY those views and
     * replaces them with the new targets list.
     * The views list should match those added in addTargets and should contain
     * one view that is not in the view hierarchy (state.nonExistentView).
     */
    public abstract void replaceTargets(@NonNull Object transitionObj,
            @SuppressLint("UnknownNullness") ArrayList<View> oldTargets,
            @SuppressLint("UnknownNullness") ArrayList<View> newTargets);

    /**
     * Adds a View target to a transition. If transitionObj is null, nothing is done.
     */
    public abstract void addTarget(@NonNull Object transitionObj, @NonNull View view);

    /**
     * Remove a View target to a transition. If transitionObj is null, nothing is done.
     */
    public abstract void removeTarget(@NonNull Object transitionObj, @NonNull View view);

    /**
     * Sets the epicenter of a transition to a rect object. The object can be modified until
     * the transition runs.
     */
    public abstract void setEpicenter(@NonNull Object transitionObj, @NonNull Rect epicenter);

    /**
     * Uses a breadth-first scheme to add startView and all of its children to views.
     * It won't add a child if it is already in views or if it has a transition name.
     */
    protected static void bfsAddViewChildren(final List<View> views, final View startView) {
        final int startIndex = views.size();
        if (containedBeforeIndex(views, startView, startIndex)) {
            return; // This child is already in the list, so all its children are also.
        }
        if (ViewCompat.getTransitionName(startView) != null) {
            views.add(startView);
        }
        for (int index = startIndex; index < views.size(); index++) {
            final View view = views.get(index);
            if (view instanceof ViewGroup) {
                ViewGroup viewGroup = (ViewGroup) view;
                final int childCount =  viewGroup.getChildCount();
                for (int childIndex = 0; childIndex < childCount; childIndex++) {
                    final View child = viewGroup.getChildAt(childIndex);
                    if (!containedBeforeIndex(views, child, startIndex)
                            && ViewCompat.getTransitionName(child) != null) {
                        views.add(child);
                    }
                }
            }
        }
    }

    /**
     * Does a linear search through views for view, limited to maxIndex.
     */
    private static boolean containedBeforeIndex(final List<View> views, final View view,
            final int maxIndex) {
        for (int i = 0; i < maxIndex; i++) {
            if (views.get(i) == view) {
                return true;
            }
        }
        return false;
    }

    /**
     * Simple utility to detect if a list is null or has no elements.
     */
    protected static boolean isNullOrEmpty(List list) {
        return list == null || list.isEmpty();
    }

}