FragmentTransition.java

/*
 * 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 android.content.Context;
import android.graphics.Rect;
import android.os.Build;
import android.util.SparseArray;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.collection.ArrayMap;
import androidx.core.app.SharedElementCallback;
import androidx.core.os.CancellationSignal;
import androidx.core.view.OneShotPreDrawListener;
import androidx.core.view.ViewCompat;

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

/**
 * Contains the Fragment Transition functionality for both ordered and reordered
 * Fragment Transactions. With reordered fragment transactions, all Views have been
 * added to the View hierarchy prior to calling startTransitions. With ordered
 * fragment transactions, Views will be removed and added after calling startTransitions.
 */
class FragmentTransition {
    /**
     * The inverse of all BackStackRecord operation commands. This assumes that
     * REPLACE operations have already been replaced by add/remove operations.
     */
    private static final int[] INVERSE_OPS = {
            BackStackRecord.OP_NULL,                // inverse of OP_NULL (error)
            BackStackRecord.OP_REMOVE,              // inverse of OP_ADD
            BackStackRecord.OP_NULL,                // inverse of OP_REPLACE (error)
            BackStackRecord.OP_ADD,                 // inverse of OP_REMOVE
            BackStackRecord.OP_SHOW,                // inverse of OP_HIDE
            BackStackRecord.OP_HIDE,                // inverse of OP_SHOW
            BackStackRecord.OP_ATTACH,              // inverse of OP_DETACH
            BackStackRecord.OP_DETACH,              // inverse of OP_ATTACH
            BackStackRecord.OP_UNSET_PRIMARY_NAV,   // inverse of OP_SET_PRIMARY_NAV
            BackStackRecord.OP_SET_PRIMARY_NAV,     // inverse of OP_UNSET_PRIMARY_NAV
            BackStackRecord.OP_SET_MAX_LIFECYCLE
    };

    /**
     * Interface to watch Fragment Transitions
     */
    interface Callback {
        /**
         * Called whenever an transition started
         */
        void onStart(@NonNull Fragment fragment, @NonNull CancellationSignal signal);

        /**
         * Called whenever an transition is complete
         */
        void onComplete(@NonNull Fragment fragment, @NonNull CancellationSignal signal);
    }

    static final FragmentTransitionImpl PLATFORM_IMPL = Build.VERSION.SDK_INT >= 21
            ? new FragmentTransitionCompat21()
            : null;

    static final FragmentTransitionImpl SUPPORT_IMPL = resolveSupportImpl();

    private static FragmentTransitionImpl resolveSupportImpl() {
        try {
            @SuppressWarnings("unchecked")
            Class<FragmentTransitionImpl> impl = (Class<FragmentTransitionImpl>) Class.forName(
                    "androidx.transition.FragmentTransitionSupport");
            return impl.getDeclaredConstructor().newInstance();
        } catch (Exception ignored) {
            // support-transition is not loaded; ignore
        }
        return null;
    }

    /**
     * The main entry point for Fragment Transitions, this starts the transitions
     * set on the leaving Fragment's {@link Fragment#getExitTransition()}, the
     * entering Fragment's {@link Fragment#getEnterTransition()} and
     * {@link Fragment#getSharedElementEnterTransition()}. When popping,
     * the leaving Fragment's {@link Fragment#getReturnTransition()} and
     * {@link Fragment#getSharedElementReturnTransition()} and the entering
     * {@link Fragment#getReenterTransition()} will be run.
     * <p>
     * With reordered Fragment Transitions, all Views have been added to the
     * View hierarchy prior to calling this method. The incoming Fragment's Views
     * will be INVISIBLE. With ordered Fragment Transitions, this method
     * is called before any change has been made to the hierarchy. That means
     * that the added Fragments have not created their Views yet and the hierarchy
     * is unknown.
     *
     * @param context The hosting context
     * @param fragmentContainer the FragmentContainer for finding the container for each Fragment
     * @param records The list of transactions being executed.
     * @param isRecordPop For each transaction, whether it is a pop transaction or not.
     * @param startIndex The first index into records and isRecordPop to execute as
     *                   part of this transition.
     * @param endIndex One past the last index into records and isRecordPop to execute
     *                 as part of this transition.
     * @param isReordered true if this is a reordered transaction, meaning that the
     *                    Views of incoming fragments have been added. false if the
     *                    transaction has yet to be run and Views haven't been created.
     */
    static void startTransitions(@NonNull Context context,
            @NonNull FragmentContainer fragmentContainer,
            ArrayList<BackStackRecord> records, ArrayList<Boolean> isRecordPop,
            int startIndex, int endIndex, boolean isReordered, Callback callback) {
        SparseArray<FragmentContainerTransition> transitioningFragments =
                new SparseArray<>();
        for (int i = startIndex; i < endIndex; i++) {
            final BackStackRecord record = records.get(i);
            final boolean isPop = isRecordPop.get(i);
            if (isPop) {
                calculatePopFragments(record, transitioningFragments, isReordered);
            } else {
                calculateFragments(record, transitioningFragments, isReordered);
            }
        }

        if (transitioningFragments.size() != 0) {
            final View nonExistentView = new View(context);
            final int numContainers = transitioningFragments.size();
            for (int i = 0; i < numContainers; i++) {
                int containerId = transitioningFragments.keyAt(i);
                ArrayMap<String, String> nameOverrides = calculateNameOverrides(containerId,
                        records, isRecordPop, startIndex, endIndex);

                FragmentContainerTransition containerTransition =
                        transitioningFragments.valueAt(i);

                if (fragmentContainer.onHasView()) {
                    ViewGroup container = (ViewGroup) fragmentContainer.onFindViewById(
                            containerId);
                    if (container == null) {
                        // No container means no transitions
                        continue;
                    }
                    if (isReordered) {
                        configureTransitionsReordered(container,
                                containerTransition, nonExistentView, nameOverrides, callback);
                    } else {
                        configureTransitionsOrdered(container,
                                containerTransition, nonExistentView, nameOverrides, callback);
                    }
                }
            }
        }
    }

    /**
     * Iterates through the transactions that affect a given fragment container
     * and tracks the shared element names across transactions. This is most useful
     * in pop transactions where the names of shared elements are known.
     *
     * @param containerId The container ID that is executing the transition.
     * @param records The list of transactions being executed.
     * @param isRecordPop For each transaction, whether it is a pop transaction or not.
     * @param startIndex The first index into records and isRecordPop to execute as
     *                   part of this transition.
     * @param endIndex One past the last index into records and isRecordPop to execute
     *                 as part of this transition.
     * @return A map from the initial shared element name to the final shared element name
     * before any onMapSharedElements is run.
     */
    private static ArrayMap<String, String> calculateNameOverrides(int containerId,
            ArrayList<BackStackRecord> records, ArrayList<Boolean> isRecordPop,
            int startIndex, int endIndex) {
        ArrayMap<String, String> nameOverrides = new ArrayMap<>();
        for (int recordNum = endIndex - 1; recordNum >= startIndex; recordNum--) {
            final BackStackRecord record = records.get(recordNum);
            if (!record.interactsWith(containerId)) {
                continue;
            }
            final boolean isPop = isRecordPop.get(recordNum);
            if (record.mSharedElementSourceNames != null) {
                final int numSharedElements = record.mSharedElementSourceNames.size();
                final ArrayList<String> sources;
                final ArrayList<String> targets;
                if (isPop) {
                    targets = record.mSharedElementSourceNames;
                    sources = record.mSharedElementTargetNames;
                } else {
                    sources = record.mSharedElementSourceNames;
                    targets = record.mSharedElementTargetNames;
                }
                for (int i = 0; i < numSharedElements; i++) {
                    String sourceName = sources.get(i);
                    String targetName = targets.get(i);
                    String previousTarget = nameOverrides.remove(targetName);
                    if (previousTarget != null) {
                        nameOverrides.put(sourceName, previousTarget);
                    } else {
                        nameOverrides.put(sourceName, targetName);
                    }
                }
            }
        }
        return nameOverrides;
    }

    /**
     * Configures a transition for a single fragment container for which the transaction was
     * reordered. That means that all Fragment Views have been added and incoming fragment
     * Views are marked invisible.
     *
     * @param container the container that the transitioning fragments are within
     * @param fragments A structure holding the transitioning fragments in this container.
     * @param nonExistentView A View that does not exist in the hierarchy. This is used to
     *                        prevent transitions from acting on other Views when there is no
     *                        other target.
     * @param nameOverrides A map of the shared element names from the starting fragment to
     *                      the final fragment's Views as given in
     *                      {@link FragmentTransaction#addSharedElement(View, String)}.
     */
    private static void configureTransitionsReordered(@NonNull ViewGroup container,
            FragmentContainerTransition fragments,
            View nonExistentView, ArrayMap<String, String> nameOverrides, final Callback callback) {
        final Fragment inFragment = fragments.lastIn;
        final Fragment outFragment = fragments.firstOut;
        final FragmentTransitionImpl impl = chooseImpl(outFragment, inFragment);
        if (impl == null) {
            return;
        }
        final boolean inIsPop = fragments.lastInIsPop;
        final boolean outIsPop = fragments.firstOutIsPop;

        ArrayList<View> sharedElementsIn = new ArrayList<>();
        ArrayList<View> sharedElementsOut = new ArrayList<>();
        Object enterTransition = getEnterTransition(impl, inFragment, inIsPop);
        Object exitTransition = getExitTransition(impl, outFragment, outIsPop);

        Object sharedElementTransition = configureSharedElementsReordered(impl, container,
                nonExistentView, nameOverrides, fragments, sharedElementsOut, sharedElementsIn,
                enterTransition, exitTransition);

        if (enterTransition == null && sharedElementTransition == null
                && exitTransition == null) {
            return; // no transitions!
        }

        ArrayList<View> exitingViews = configureEnteringExitingViews(impl, exitTransition,
                outFragment, sharedElementsOut, nonExistentView);

        ArrayList<View> enteringViews = configureEnteringExitingViews(impl, enterTransition,
                inFragment, sharedElementsIn, nonExistentView);

        setViewVisibility(enteringViews, View.INVISIBLE);

        Object transition = mergeTransitions(impl, enterTransition, exitTransition,
                sharedElementTransition, inFragment, inIsPop);

        if (outFragment != null && exitingViews != null
                && (exitingViews.size() > 0 || sharedElementsOut.size() > 0)) {
            final CancellationSignal signal = new CancellationSignal();
            callback.onStart(outFragment, signal);
            impl.setListenerForTransitionEnd(outFragment, transition, signal, new Runnable() {
                @Override
                public void run() {
                    callback.onComplete(outFragment, signal);
                }
            });
        }

        if (transition != null) {
            replaceHide(impl, exitTransition, outFragment, exitingViews);
            ArrayList<String> inNames =
                    impl.prepareSetNameOverridesReordered(sharedElementsIn);
            impl.scheduleRemoveTargets(transition,
                    enterTransition, enteringViews, exitTransition, exitingViews,
                    sharedElementTransition, sharedElementsIn);
            impl.beginDelayedTransition(container, transition);
            impl.setNameOverridesReordered(container, sharedElementsOut,
                    sharedElementsIn, inNames, nameOverrides);
            setViewVisibility(enteringViews, View.VISIBLE);
            impl.swapSharedElementTargets(sharedElementTransition,
                    sharedElementsOut, sharedElementsIn);
        }
    }

    /**
     * Replace hide operations with visibility changes on the exiting views. Instead of making
     * the entire fragment's view GONE, make each exiting view INVISIBLE. At the end of the
     * transition, make the fragment's view GONE.
     */
    private static void replaceHide(FragmentTransitionImpl impl,
            Object exitTransition, Fragment exitingFragment,
            final ArrayList<View> exitingViews) {
        if (exitingFragment != null && exitTransition != null && exitingFragment.mAdded
                && exitingFragment.mHidden && exitingFragment.mHiddenChanged) {
            exitingFragment.setHideReplaced(true);
            impl.scheduleHideFragmentView(exitTransition,
                    exitingFragment.getView(), exitingViews);
            /* This is required to indicate to the TransitionManager the desired end state of the
             scene when a hide is used. In the replace case, the exiting Fragment's view is
             removed from the sceneRoot during the delay, and the TransitionManager is able to
             calculate the difference between the two switching views. Because we can have
             exiting child views with transitions, we cannot just mark the entire exiting
             Fragment view as INVISIBLE or the TransitionManager will not consider the views
             individually.

            This OneShotPreDrawListener gets fired before the delayed start of the Transition and
             changes the visibility of any exiting child views that *ARE NOT* shared element
             transitions. The TransitionManager then properly considers exiting views and marks
             them as disappearing, applying a transition and a listener to take proper actions
             once the transition is complete.
            */

            final ViewGroup container = exitingFragment.mContainer;
            OneShotPreDrawListener.add(container, new Runnable() {
                @Override
                public void run() {
                    setViewVisibility(exitingViews, View.INVISIBLE);
                }
            });
        }
    }

    /**
     * Configures a transition for a single fragment container for which the transaction was
     * ordered. That means that the transaction has not been executed yet, so incoming
     * Views are not yet known.
     *
     * @param container the container that the transitioning fragments are within
     * @param fragments A structure holding the transitioning fragments in this container.
     * @param nonExistentView A View that does not exist in the hierarchy. This is used to
     *                        prevent transitions from acting on other Views when there is no
     *                        other target.
     * @param nameOverrides A map of the shared element names from the starting fragment to
     *                      the final fragment's Views as given in
     *                      {@link FragmentTransaction#addSharedElement(View, String)}.
     */
    private static void configureTransitionsOrdered(@NonNull ViewGroup container,
            FragmentContainerTransition fragments,
            View nonExistentView, ArrayMap<String, String> nameOverrides, final Callback callback) {
        final Fragment inFragment = fragments.lastIn;
        final Fragment outFragment = fragments.firstOut;
        final FragmentTransitionImpl impl = chooseImpl(outFragment, inFragment);
        if (impl == null) {
            return;
        }
        final boolean inIsPop = fragments.lastInIsPop;
        final boolean outIsPop = fragments.firstOutIsPop;

        Object enterTransition = getEnterTransition(impl, inFragment, inIsPop);
        Object exitTransition = getExitTransition(impl, outFragment, outIsPop);

        ArrayList<View> sharedElementsOut = new ArrayList<>();
        ArrayList<View> sharedElementsIn = new ArrayList<>();

        Object sharedElementTransition = configureSharedElementsOrdered(impl, container,
                nonExistentView, nameOverrides, fragments, sharedElementsOut, sharedElementsIn,
                enterTransition, exitTransition);

        if (enterTransition == null && sharedElementTransition == null
                && exitTransition == null) {
            return; // no transitions!
        }

        ArrayList<View> exitingViews = configureEnteringExitingViews(impl, exitTransition,
                outFragment, sharedElementsOut, nonExistentView);

        if (exitingViews == null || exitingViews.isEmpty()) {
            exitTransition = null;
        }

        // Ensure the entering transition doesn't target anything until the views are made
        // visible
        impl.addTarget(enterTransition, nonExistentView);

        Object transition = mergeTransitions(impl, enterTransition, exitTransition,
                sharedElementTransition, inFragment, fragments.lastInIsPop);

        if (outFragment != null && exitingViews != null
                && (exitingViews.size() > 0 || sharedElementsOut.size() > 0)) {
            final CancellationSignal signal = new CancellationSignal();
            callback.onStart(outFragment, signal);
            impl.setListenerForTransitionEnd(outFragment, transition, signal, new Runnable() {
                @Override
                public void run() {
                    callback.onComplete(outFragment, signal);
                }
            });
        }

        if (transition != null) {
            final ArrayList<View> enteringViews = new ArrayList<>();
            impl.scheduleRemoveTargets(transition,
                    enterTransition, enteringViews, exitTransition, exitingViews,
                    sharedElementTransition, sharedElementsIn);
            scheduleTargetChange(impl, container, inFragment, nonExistentView, sharedElementsIn,
                    enterTransition, enteringViews, exitTransition, exitingViews);
            impl.setNameOverridesOrdered(container, sharedElementsIn, nameOverrides);

            impl.beginDelayedTransition(container, transition);
            impl.scheduleNameReset(container, sharedElementsIn, nameOverrides);
        }
    }

    /**
     * This method is used for fragment transitions for ordrered transactions to change the
     * enter and exit transition targets after the call to
     * {@link FragmentTransitionCompat21#beginDelayedTransition(ViewGroup, Object)}. The exit
     * transition must ensure that it does not target any Views and the enter transition must start
     * targeting the Views of the incoming Fragment.
     *
     * @param sceneRoot The fragment container View
     * @param inFragment The last fragment that is entering
     * @param nonExistentView A view that does not exist in the hierarchy that is used as a
     *                        transition target to ensure no View is targeted.
     * @param sharedElementsIn The shared element Views of the incoming fragment
     * @param enterTransition The enter transition of the incoming fragment
     * @param enteringViews The entering Views of the incoming fragment
     * @param exitTransition The exit transition of the outgoing fragment
     * @param exitingViews The exiting views of the outgoing fragment
     */
    private static void scheduleTargetChange(final FragmentTransitionImpl impl,
            final ViewGroup sceneRoot,
            final Fragment inFragment, final View nonExistentView,
            final ArrayList<View> sharedElementsIn,
            final Object enterTransition, final ArrayList<View> enteringViews,
            final Object exitTransition, final ArrayList<View> exitingViews) {
        OneShotPreDrawListener.add(sceneRoot, new Runnable() {
            @Override
            public void run() {
                if (enterTransition != null) {
                    impl.removeTarget(enterTransition,
                            nonExistentView);
                    ArrayList<View> views = configureEnteringExitingViews(impl,
                            enterTransition, inFragment, sharedElementsIn, nonExistentView);
                    enteringViews.addAll(views);
                }

                if (exitingViews != null) {
                    if (exitTransition != null) {
                        ArrayList<View> tempExiting = new ArrayList<>();
                        tempExiting.add(nonExistentView);
                        impl.replaceTargets(exitTransition, exitingViews,
                                tempExiting);
                    }
                    exitingViews.clear();
                    exitingViews.add(nonExistentView);
                }
            }
        });
    }

    /**
     * Chooses the appropriate implementation depending on the Transition instances hold by the
     * Fragments.
     */
    private static FragmentTransitionImpl chooseImpl(Fragment outFragment, Fragment inFragment) {
        // Collect all transition instances
        final ArrayList<Object> transitions = new ArrayList<>();
        if (outFragment != null) {
            final Object exitTransition = outFragment.getExitTransition();
            if (exitTransition != null) {
                transitions.add(exitTransition);
            }
            final Object returnTransition = outFragment.getReturnTransition();
            if (returnTransition != null) {
                transitions.add(returnTransition);
            }
            final Object sharedReturnTransition = outFragment.getSharedElementReturnTransition();
            if (sharedReturnTransition != null) {
                transitions.add(sharedReturnTransition);
            }
        }
        if (inFragment != null) {
            final Object enterTransition = inFragment.getEnterTransition();
            if (enterTransition != null) {
                transitions.add(enterTransition);
            }
            final Object reenterTransition = inFragment.getReenterTransition();
            if (reenterTransition != null) {
                transitions.add(reenterTransition);
            }
            final Object sharedEnterTransition = inFragment.getSharedElementEnterTransition();
            if (sharedEnterTransition != null) {
                transitions.add(sharedEnterTransition);
            }
        }
        if (transitions.isEmpty()) {
            return null; // No transition to run
        }
        // Pick the implementation that can handle all the transitions
        if (PLATFORM_IMPL != null && canHandleAll(PLATFORM_IMPL, transitions)) {
            return PLATFORM_IMPL;
        }
        if (SUPPORT_IMPL != null && canHandleAll(SUPPORT_IMPL, transitions)) {
            return SUPPORT_IMPL;
        }
        if (PLATFORM_IMPL != null || SUPPORT_IMPL != null) {
            throw new IllegalArgumentException("Invalid Transition types");
        }
        return null;
    }

    private static boolean canHandleAll(FragmentTransitionImpl impl, List<Object> transitions) {
        for (int i = 0, size = transitions.size(); i < size; i++) {
            if (!impl.canHandle(transitions.get(i))) {
                return false;
            }
        }
        return true;
    }

    /**
     * Returns a TransitionSet containing the shared element transition. The wrapping TransitionSet
     * targets all shared elements to ensure that no other Views are targeted. The shared element
     * transition can then target any or all shared elements without worrying about accidentally
     * targeting entering or exiting Views.
     *
     * @param inFragment The incoming fragment
     * @param outFragment the outgoing fragment
     * @param isPop True if this is a pop transaction or false if it is a normal (add) transaction.
     * @return A TransitionSet wrapping the shared element transition or null if no such transition
     * exists.
     */
    private static Object getSharedElementTransition(FragmentTransitionImpl impl,
            Fragment inFragment, Fragment outFragment, boolean isPop) {
        if (inFragment == null || outFragment == null) {
            return null;
        }
        Object transition = impl.cloneTransition(isPop
                ? outFragment.getSharedElementReturnTransition()
                : inFragment.getSharedElementEnterTransition());
        return impl.wrapTransitionInSet(transition);
    }

    /**
     * Returns a clone of the enter transition or null if no such transition exists.
     */
    private static Object getEnterTransition(FragmentTransitionImpl impl,
            Fragment inFragment, boolean isPop) {
        if (inFragment == null) {
            return null;
        }
        return impl.cloneTransition(isPop
                ? inFragment.getReenterTransition()
                : inFragment.getEnterTransition());
    }

    /**
     * Returns a clone of the exit transition or null if no such transition exists.
     */
    private static Object getExitTransition(FragmentTransitionImpl impl,
            Fragment outFragment, boolean isPop) {
        if (outFragment == null) {
            return null;
        }
        return impl.cloneTransition(isPop
                ? outFragment.getReturnTransition()
                : outFragment.getExitTransition());
    }

    /**
     * Configures the shared elements of a reordered fragment transaction's transition.
     * This retrieves the shared elements of the outgoing and incoming fragments, maps the
     * views, and sets up the epicenter on the transitions.
     * <p>
     * The epicenter of exit and shared element transitions is the first shared element
     * in the outgoing fragment. The epicenter of the entering transition is the first shared
     * element in the incoming fragment.
     *
     * @param sceneRoot The fragment container View
     * @param nonExistentView A View that does not exist in the hierarchy. This is used to
     *                        prevent transitions from acting on other Views when there is no
     *                        other target.
     * @param nameOverrides A map of the shared element names from the starting fragment to
     *                      the final fragment's Views as given in
     *                      {@link FragmentTransaction#addSharedElement(View, String)}.
     * @param fragments A structure holding the transitioning fragments in this container.
     * @param sharedElementsOut A list modified to contain the shared elements in the outgoing
     *                          fragment
     * @param sharedElementsIn A list modified to contain the shared elements in the incoming
     *                         fragment
     * @param enterTransition The transition used for entering Views, modified by applying the
     *                        epicenter
     * @param exitTransition The transition used for exiting Views, modified by applying the
     *                       epicenter
     * @return The shared element transition or null if no shared elements exist
     */
    private static Object configureSharedElementsReordered(final FragmentTransitionImpl impl,
            final ViewGroup sceneRoot,
            final View nonExistentView, final ArrayMap<String, String> nameOverrides,
            final FragmentContainerTransition fragments,
            final ArrayList<View> sharedElementsOut,
            final ArrayList<View> sharedElementsIn,
            final Object enterTransition, final Object exitTransition) {
        final Fragment inFragment = fragments.lastIn;
        final Fragment outFragment = fragments.firstOut;
        if (inFragment != null) {
            inFragment.requireView().setVisibility(View.VISIBLE);
        }
        if (inFragment == null || outFragment == null) {
            return null; // no shared element without a fragment
        }

        final boolean inIsPop = fragments.lastInIsPop;
        Object sharedElementTransition = nameOverrides.isEmpty() ? null
                : getSharedElementTransition(impl, inFragment, outFragment, inIsPop);

        final ArrayMap<String, View> outSharedElements = captureOutSharedElements(impl,
                nameOverrides, sharedElementTransition, fragments);

        final ArrayMap<String, View> inSharedElements = captureInSharedElements(impl,
                nameOverrides, sharedElementTransition, fragments);

        if (nameOverrides.isEmpty()) {
            sharedElementTransition = null;
            if (outSharedElements != null) {
                outSharedElements.clear();
            }
            if (inSharedElements != null) {
                inSharedElements.clear();
            }
        } else {
            addSharedElementsWithMatchingNames(sharedElementsOut, outSharedElements,
                    nameOverrides.keySet());
            addSharedElementsWithMatchingNames(sharedElementsIn, inSharedElements,
                    nameOverrides.values());
        }

        if (enterTransition == null && exitTransition == null && sharedElementTransition == null) {
            // don't call onSharedElementStart/End since there is no transition
            return null;
        }

        callSharedElementStartEnd(inFragment, outFragment, inIsPop, outSharedElements, true);

        final Rect epicenter;
        final View epicenterView;
        if (sharedElementTransition != null) {
            sharedElementsIn.add(nonExistentView);
            impl.setSharedElementTargets(sharedElementTransition,
                    nonExistentView, sharedElementsOut);
            final boolean outIsPop = fragments.firstOutIsPop;
            final BackStackRecord outTransaction = fragments.firstOutTransaction;
            setOutEpicenter(impl, sharedElementTransition, exitTransition, outSharedElements,
                    outIsPop, outTransaction);
            epicenter = new Rect();
            epicenterView = getInEpicenterView(inSharedElements, fragments,
                    enterTransition, inIsPop);
            if (epicenterView != null) {
                impl.setEpicenter(enterTransition, epicenter);
            }
        } else {
            epicenter = null;
            epicenterView = null;
        }

        OneShotPreDrawListener.add(sceneRoot, new Runnable() {
            @Override
            public void run() {
                callSharedElementStartEnd(inFragment, outFragment, inIsPop,
                        inSharedElements, false);
                if (epicenterView != null) {
                    impl.getBoundsOnScreen(epicenterView, epicenter);
                }
            }
        });
        return sharedElementTransition;
    }

    /**
     * Add Views from sharedElements into views that have the transitionName in the
     * nameOverridesSet.
     *
     * @param views               Views list to add shared elements to
     * @param sharedElements      List of shared elements
     * @param nameOverridesSet    The transition names for all views to be copied from
     *                            sharedElements to views.
     */
    private static void addSharedElementsWithMatchingNames(ArrayList<View> views,
            ArrayMap<String, View> sharedElements, Collection<String> nameOverridesSet) {
        for (int i = sharedElements.size() - 1; i >= 0; i--) {
            View view = sharedElements.valueAt(i);
            if (nameOverridesSet.contains(ViewCompat.getTransitionName(view))) {
                views.add(view);
            }
        }
    }

    /**
     * Configures the shared elements of an ordered fragment transaction's transition.
     * This retrieves the shared elements of the incoming fragments, and schedules capturing
     * the incoming fragment's shared elements. It also maps the views, and sets up the epicenter
     * on the transitions.
     * <p>
     * The epicenter of exit and shared element transitions is the first shared element
     * in the outgoing fragment. The epicenter of the entering transition is the first shared
     * element in the incoming fragment.
     *
     * @param sceneRoot The fragment container View
     * @param nonExistentView A View that does not exist in the hierarchy. This is used to
     *                        prevent transitions from acting on other Views when there is no
     *                        other target.
     * @param nameOverrides A map of the shared element names from the starting fragment to
     *                      the final fragment's Views as given in
     *                      {@link FragmentTransaction#addSharedElement(View, String)}.
     * @param fragments A structure holding the transitioning fragments in this container.
     * @param sharedElementsOut A list modified to contain the shared elements in the outgoing
     *                          fragment
     * @param sharedElementsIn A list modified to contain the shared elements in the incoming
     *                         fragment
     * @param enterTransition The transition used for entering Views, modified by applying the
     *                        epicenter
     * @param exitTransition The transition used for exiting Views, modified by applying the
     *                       epicenter
     * @return The shared element transition or null if no shared elements exist
     */
    private static Object configureSharedElementsOrdered(final FragmentTransitionImpl impl,
            final ViewGroup sceneRoot,
            final View nonExistentView, final ArrayMap<String, String> nameOverrides,
            final FragmentContainerTransition fragments,
            final ArrayList<View> sharedElementsOut,
            final ArrayList<View> sharedElementsIn,
            final Object enterTransition, final Object exitTransition) {
        final Fragment inFragment = fragments.lastIn;
        final Fragment outFragment = fragments.firstOut;

        if (inFragment == null || outFragment == null) {
            return null; // no transition
        }

        final boolean inIsPop = fragments.lastInIsPop;
        Object sharedElementTransition = nameOverrides.isEmpty() ? null
                : getSharedElementTransition(impl, inFragment, outFragment, inIsPop);

        ArrayMap<String, View> outSharedElements = captureOutSharedElements(impl, nameOverrides,
                sharedElementTransition, fragments);

        if (nameOverrides.isEmpty()) {
            sharedElementTransition = null;
        } else {
            sharedElementsOut.addAll(outSharedElements.values());
        }

        if (enterTransition == null && exitTransition == null && sharedElementTransition == null) {
            // don't call onSharedElementStart/End since there is no transition
            return null;
        }

        callSharedElementStartEnd(inFragment, outFragment, inIsPop, outSharedElements, true);

        final Rect inEpicenter;
        if (sharedElementTransition != null) {
            inEpicenter = new Rect();
            impl.setSharedElementTargets(sharedElementTransition,
                    nonExistentView, sharedElementsOut);
            final boolean outIsPop = fragments.firstOutIsPop;
            final BackStackRecord outTransaction = fragments.firstOutTransaction;
            setOutEpicenter(impl, sharedElementTransition, exitTransition, outSharedElements,
                    outIsPop, outTransaction);
            if (enterTransition != null) {
                impl.setEpicenter(enterTransition, inEpicenter);
            }
        } else {
            inEpicenter = null;
        }


        final Object finalSharedElementTransition = sharedElementTransition;
        OneShotPreDrawListener.add(sceneRoot, new Runnable() {
            @Override
            public void run() {
                ArrayMap<String, View> inSharedElements = captureInSharedElements(impl,
                        nameOverrides, finalSharedElementTransition, fragments);

                if (inSharedElements != null) {
                    sharedElementsIn.addAll(inSharedElements.values());
                    sharedElementsIn.add(nonExistentView);
                }

                callSharedElementStartEnd(inFragment, outFragment, inIsPop,
                        inSharedElements, false);
                if (finalSharedElementTransition != null) {
                    impl.swapSharedElementTargets(
                            finalSharedElementTransition, sharedElementsOut,
                            sharedElementsIn);

                    final View inEpicenterView = getInEpicenterView(inSharedElements,
                            fragments, enterTransition, inIsPop);
                    if (inEpicenterView != null) {
                        impl.getBoundsOnScreen(inEpicenterView,
                                inEpicenter);
                    }
                }
            }
        });

        return sharedElementTransition;
    }

    /**
     * Finds the shared elements in the outgoing fragment. It also calls
     * {@link SharedElementCallback#onMapSharedElements(List, Map)} to allow more control
     * of the shared element mapping. {@code nameOverrides} is updated to match the
     * actual transition name of the mapped shared elements.
     *
     * @param nameOverrides A map of the shared element names from the starting fragment to
     *                      the final fragment's Views as given in
     *                      {@link FragmentTransaction#addSharedElement(View, String)}.
     * @param sharedElementTransition The shared element transition
     * @param fragments A structure holding the transitioning fragments in this container.
     * @return The mapping of shared element names to the Views in the hierarchy or null
     * if there is no shared element transition.
     */
    private static ArrayMap<String, View> captureOutSharedElements(FragmentTransitionImpl impl,
            ArrayMap<String, String> nameOverrides, Object sharedElementTransition,
            FragmentContainerTransition fragments) {
        if (nameOverrides.isEmpty() || sharedElementTransition == null) {
            nameOverrides.clear();
            return null;
        }
        final Fragment outFragment = fragments.firstOut;
        final ArrayMap<String, View> outSharedElements = new ArrayMap<>();
        impl.findNamedViews(outSharedElements, outFragment.requireView());

        final SharedElementCallback sharedElementCallback;
        final ArrayList<String> names;
        final BackStackRecord outTransaction = fragments.firstOutTransaction;
        if (fragments.firstOutIsPop) {
            sharedElementCallback = outFragment.getEnterTransitionCallback();
            names = outTransaction.mSharedElementTargetNames;
        } else {
            sharedElementCallback = outFragment.getExitTransitionCallback();
            names = outTransaction.mSharedElementSourceNames;
        }

        if (names != null) {
            outSharedElements.retainAll(names);
        }
        if (sharedElementCallback != null) {
            sharedElementCallback.onMapSharedElements(names, outSharedElements);
            for (int i = names.size() - 1; i >= 0; i--) {
                String name = names.get(i);
                View view = outSharedElements.get(name);
                if (view == null) {
                    nameOverrides.remove(name);
                } else if (!name.equals(ViewCompat.getTransitionName(view))) {
                    String targetValue = nameOverrides.remove(name);
                    nameOverrides.put(ViewCompat.getTransitionName(view), targetValue);
                }
            }
        } else {
            nameOverrides.retainAll(outSharedElements.keySet());
        }
        return outSharedElements;
    }

    /**
     * Finds the shared elements in the incoming fragment. It also calls
     * {@link SharedElementCallback#onMapSharedElements(List, Map)} to allow more control
     * of the shared element mapping. {@code nameOverrides} is updated to match the
     * actual transition name of the mapped shared elements.
     *
     * @param nameOverrides A map of the shared element names from the starting fragment to
     *                      the final fragment's Views as given in
     *                      {@link FragmentTransaction#addSharedElement(View, String)}.
     * @param sharedElementTransition The shared element transition
     * @param fragments A structure holding the transitioning fragments in this container.
     * @return The mapping of shared element names to the Views in the hierarchy or null
     * if there is no shared element transition.
     */
    @SuppressWarnings("WeakerAccess") /* synthetic access */
    static ArrayMap<String, View> captureInSharedElements(FragmentTransitionImpl impl,
            ArrayMap<String, String> nameOverrides, Object sharedElementTransition,
            FragmentContainerTransition fragments) {
        Fragment inFragment = fragments.lastIn;
        final View fragmentView = inFragment.getView();
        if (nameOverrides.isEmpty() || sharedElementTransition == null || fragmentView == null) {
            nameOverrides.clear();
            return null;
        }
        final ArrayMap<String, View> inSharedElements = new ArrayMap<>();
        impl.findNamedViews(inSharedElements, fragmentView);

        final SharedElementCallback sharedElementCallback;
        final ArrayList<String> names;
        final BackStackRecord inTransaction = fragments.lastInTransaction;
        if (fragments.lastInIsPop) {
            sharedElementCallback = inFragment.getExitTransitionCallback();
            names = inTransaction.mSharedElementSourceNames;
        } else {
            sharedElementCallback = inFragment.getEnterTransitionCallback();
            names = inTransaction.mSharedElementTargetNames;
        }

        if (names != null) {
            inSharedElements.retainAll(names);
            inSharedElements.retainAll(nameOverrides.values());
        }
        if (sharedElementCallback != null) {
            sharedElementCallback.onMapSharedElements(names, inSharedElements);
            for (int i = names.size() - 1; i >= 0; i--) {
                String name = names.get(i);
                View view = inSharedElements.get(name);
                if (view == null) {
                    String key = findKeyForValue(nameOverrides, name);
                    if (key != null) {
                        nameOverrides.remove(key);
                    }
                } else if (!name.equals(ViewCompat.getTransitionName(view))) {
                    String key = findKeyForValue(nameOverrides, name);
                    if (key != null) {
                        nameOverrides.put(key, ViewCompat.getTransitionName(view));
                    }
                }
            }
        } else {
            retainValues(nameOverrides, inSharedElements);
        }
        return inSharedElements;
    }

    /**
     * Utility to find the String key in {@code map} that maps to {@code value}.
     */
    static String findKeyForValue(ArrayMap<String, String> map, String value) {
        final int numElements = map.size();
        for (int i = 0; i < numElements; i++) {
            if (value.equals(map.valueAt(i))) {
                return map.keyAt(i);
            }
        }
        return null;
    }

    /**
     * Returns the View in the incoming Fragment that should be used as the epicenter.
     *
     * @param inSharedElements The mapping of shared element names to Views in the
     *                         incoming fragment.
     * @param fragments A structure holding the transitioning fragments in this container.
     * @param enterTransition The transition used for the incoming Fragment's views
     * @param inIsPop Is the incoming fragment being added as a pop transaction?
     */
    @SuppressWarnings("WeakerAccess") /* synthetic access */
    static View getInEpicenterView(ArrayMap<String, View> inSharedElements,
            FragmentContainerTransition fragments,
            Object enterTransition, boolean inIsPop) {
        BackStackRecord inTransaction = fragments.lastInTransaction;
        if (enterTransition != null && inSharedElements != null
                && inTransaction.mSharedElementSourceNames != null
                && !inTransaction.mSharedElementSourceNames.isEmpty()) {
            final String targetName = inIsPop
                    ? inTransaction.mSharedElementSourceNames.get(0)
                    : inTransaction.mSharedElementTargetNames.get(0);
            return inSharedElements.get(targetName);
        }
        return null;
    }

    /**
     * Sets the epicenter for the exit transition.
     *
     * @param sharedElementTransition The shared element transition
     * @param exitTransition The transition for the outgoing fragment's views
     * @param outSharedElements Shared elements in the outgoing fragment
     * @param outIsPop Is the outgoing fragment being removed as a pop transaction?
     * @param outTransaction The transaction that caused the fragment to be removed.
     */
    private static void setOutEpicenter(FragmentTransitionImpl impl, Object sharedElementTransition,
            Object exitTransition, ArrayMap<String, View> outSharedElements, boolean outIsPop,
            BackStackRecord outTransaction) {
        if (outTransaction.mSharedElementSourceNames != null
                && !outTransaction.mSharedElementSourceNames.isEmpty()) {
            final String sourceName = outIsPop
                    ? outTransaction.mSharedElementTargetNames.get(0)
                    : outTransaction.mSharedElementSourceNames.get(0);
            final View outEpicenterView = outSharedElements.get(sourceName);
            impl.setEpicenter(sharedElementTransition, outEpicenterView);

            if (exitTransition != null) {
                impl.setEpicenter(exitTransition, outEpicenterView);
            }
        }
    }

    /**
     * A utility to retain only the mappings in {@code nameOverrides} that have a value
     * that has a key in {@code namedViews}. This is a useful equivalent to
     * {@link ArrayMap#retainAll(Collection)} for values.
     */
    static void retainValues(@NonNull ArrayMap<String, String> nameOverrides,
            @NonNull ArrayMap<String, View> namedViews) {
        for (int i = nameOverrides.size() - 1; i >= 0; i--) {
            final String targetName = nameOverrides.valueAt(i);
            if (!namedViews.containsKey(targetName)) {
                nameOverrides.removeAt(i);
            }
        }
    }

    /**
     * Calls the {@link SharedElementCallback#onSharedElementStart(List, List, List)} or
     * {@link SharedElementCallback#onSharedElementEnd(List, List, List)} on the appropriate
     * incoming or outgoing fragment.
     *
     * @param inFragment The incoming fragment
     * @param outFragment The outgoing fragment
     * @param isPop Is the incoming fragment part of a pop transaction?
     * @param sharedElements The shared element Views
     * @param isStart Call the start or end call on the SharedElementCallback
     */
    @SuppressWarnings("WeakerAccess") /* synthetic access */
    static void callSharedElementStartEnd(Fragment inFragment, Fragment outFragment,
            boolean isPop, ArrayMap<String, View> sharedElements, boolean isStart) {
        SharedElementCallback sharedElementCallback = isPop
                ? outFragment.getEnterTransitionCallback()
                : inFragment.getEnterTransitionCallback();
        if (sharedElementCallback != null) {
            ArrayList<View> views = new ArrayList<>();
            ArrayList<String> names = new ArrayList<>();
            final int count = sharedElements == null ? 0 : sharedElements.size();
            for (int i = 0; i < count; i++) {
                names.add(sharedElements.keyAt(i));
                views.add(sharedElements.valueAt(i));
            }
            if (isStart) {
                sharedElementCallback.onSharedElementStart(names, views, null);
            } else {
                sharedElementCallback.onSharedElementEnd(names, views, null);
            }
        }
    }

    @SuppressWarnings("WeakerAccess") /* synthetic access */
    static ArrayList<View> configureEnteringExitingViews(FragmentTransitionImpl impl,
            Object transition,
            Fragment fragment, ArrayList<View> sharedElements, View nonExistentView) {
        ArrayList<View> viewList = null;
        if (transition != null) {
            viewList = new ArrayList<>();
            View root = fragment.getView();
            if (root != null) {
                impl.captureTransitioningViews(viewList, root);
            }
            if (sharedElements != null) {
                viewList.removeAll(sharedElements);
            }
            if (!viewList.isEmpty()) {
                viewList.add(nonExistentView);
                impl.addTargets(transition, viewList);
            }
        }
        return viewList;
    }

    /**
     * Sets the visibility of all Views in {@code views} to {@code visibility}.
     */
    static void setViewVisibility(ArrayList<View> views, int visibility) {
        if (views == null) {
            return;
        }
        for (int i = views.size() - 1; i >= 0; i--) {
            final View view = views.get(i);
            view.setVisibility(visibility);
        }
    }

    /**
     * Merges exit, shared element, and enter transitions so that they act together or
     * sequentially as defined in the fragments.
     */
    private static Object mergeTransitions(FragmentTransitionImpl impl, Object enterTransition,
            Object exitTransition, Object sharedElementTransition, Fragment inFragment,
            boolean isPop) {
        boolean overlap = true;
        if (enterTransition != null && exitTransition != null && inFragment != null) {
            overlap = isPop ? inFragment.getAllowReturnTransitionOverlap() :
                    inFragment.getAllowEnterTransitionOverlap();
        }

        // Wrap the transitions. Explicit targets like in enter and exit will cause the
        // views to be targeted regardless of excluded views. If that happens, then the
        // excluded fragments views (hidden fragments) will still be in the transition.

        Object transition;
        if (overlap) {
            // Regular transition -- do it all together
            transition = impl.mergeTransitionsTogether(exitTransition,
                    enterTransition, sharedElementTransition);
        } else {
            // First do exit, then enter, but allow shared element transition to happen
            // during both.
            transition = impl.mergeTransitionsInSequence(exitTransition,
                    enterTransition, sharedElementTransition);
        }
        return transition;
    }

    /**
     * Finds the first removed fragment and last added fragments when going forward.
     * If none of the fragments have transitions, then both lists will be empty.
     *
     * @param transitioningFragments Keyed on the container ID, the first fragments to be removed,
     *                               and last fragments to be added. This will be modified by
     *                               this method.
     */
    public static void calculateFragments(BackStackRecord transaction,
            SparseArray<FragmentContainerTransition> transitioningFragments,
            boolean isReordered) {
        final int numOps = transaction.mOps.size();
        for (int opNum = 0; opNum < numOps; opNum++) {
            final BackStackRecord.Op op = transaction.mOps.get(opNum);
            addToFirstInLastOut(transaction, op, transitioningFragments, false, isReordered);
        }
    }

    /**
     * Finds the first removed fragment and last added fragments when popping the back stack.
     * If none of the fragments have transitions, then both lists will be empty.
     *
     * @param transitioningFragments Keyed on the container ID, the first fragments to be removed,
     *                               and last fragments to be added. This will be modified by
     *                               this method.
     */
    public static void calculatePopFragments(BackStackRecord transaction,
            SparseArray<FragmentContainerTransition> transitioningFragments, boolean isReordered) {
        if (!transaction.mManager.getContainer().onHasView()) {
            return; // nothing to see, so no transitions
        }
        final int numOps = transaction.mOps.size();
        for (int opNum = numOps - 1; opNum >= 0; opNum--) {
            final BackStackRecord.Op op = transaction.mOps.get(opNum);
            addToFirstInLastOut(transaction, op, transitioningFragments, true, isReordered);
        }
    }

    static boolean supportsTransition() {
        return PLATFORM_IMPL != null || SUPPORT_IMPL != null;
    }

    /**
     * Examines the {@code command} and may set the first out or last in fragment for the fragment's
     * container.
     *
     * @param transaction The executing transaction
     * @param op The operation being run.
     * @param transitioningFragments A structure holding the first in and last out fragments
     *                               for each fragment container.
     * @param isPop Is the operation a pop?
     * @param isReorderedTransaction True if the operations have been partially executed and the
     *                               added fragments have Views in the hierarchy or false if the
     *                               operations haven't been executed yet.
     */
    @SuppressWarnings("ReferenceEquality")
    private static void addToFirstInLastOut(BackStackRecord transaction, BackStackRecord.Op op,
            SparseArray<FragmentContainerTransition> transitioningFragments, boolean isPop,
            boolean isReorderedTransaction) {
        final Fragment fragment = op.mFragment;
        if (fragment == null) {
            return; // no fragment, no transition
        }
        final int containerId = fragment.mContainerId;
        if (containerId == 0) {
            return; // no container, no transition
        }
        final int command = isPop ? INVERSE_OPS[op.mCmd] : op.mCmd;
        boolean setLastIn = false;
        boolean wasRemoved = false;
        boolean setFirstOut = false;
        boolean wasAdded = false;
        switch (command) {
            case BackStackRecord.OP_SHOW:
                if (isReorderedTransaction) {
                    setLastIn = fragment.mHiddenChanged && !fragment.mHidden && fragment.mAdded;
                } else {
                    setLastIn = fragment.mHidden;
                }
                wasAdded = true;
                break;
            case BackStackRecord.OP_ADD:
            case BackStackRecord.OP_ATTACH:
                if (isReorderedTransaction) {
                    setLastIn = fragment.mIsNewlyAdded;
                } else {
                    setLastIn = !fragment.mAdded && !fragment.mHidden;
                }
                wasAdded = true;
                break;
            case BackStackRecord.OP_HIDE:
                if (isReorderedTransaction) {
                    setFirstOut = fragment.mHiddenChanged && fragment.mAdded && fragment.mHidden;
                } else {
                    setFirstOut = fragment.mAdded && !fragment.mHidden;
                }
                wasRemoved = true;
                break;
            case BackStackRecord.OP_REMOVE:
            case BackStackRecord.OP_DETACH:
                if (isReorderedTransaction) {
                    setFirstOut = !fragment.mAdded && fragment.mView != null
                            && fragment.mView.getVisibility() == View.VISIBLE
                            && fragment.mPostponedAlpha >= 0;
                } else {
                    setFirstOut = fragment.mAdded && !fragment.mHidden;
                }
                wasRemoved = true;
                break;
        }
        FragmentContainerTransition containerTransition = transitioningFragments.get(containerId);
        if (setLastIn) {
            containerTransition =
                    ensureContainer(containerTransition, transitioningFragments, containerId);
            containerTransition.lastIn = fragment;
            containerTransition.lastInIsPop = isPop;
            containerTransition.lastInTransaction = transaction;
        }
        if (!isReorderedTransaction && wasAdded) {
            if (containerTransition != null && containerTransition.firstOut == fragment) {
                containerTransition.firstOut = null;
            }

            if (!transaction.mReorderingAllowed) {
                // When reordering isn't allowed, we may be starting Transitions before
                // the Fragment operation is actually executed so we move any new Fragments
                // to created here first so that they have a Context, etc. when they
                // are asked to load their Transitions
                FragmentManager manager = transaction.mManager;
                FragmentStateManager fragmentStateManager =
                        manager.createOrGetFragmentStateManager(fragment);
                manager.getFragmentStore().makeActive(fragmentStateManager);
                manager.moveToState(fragment);
            }
        }
        if (setFirstOut && (containerTransition == null || containerTransition.firstOut == null)) {
            containerTransition =
                    ensureContainer(containerTransition, transitioningFragments, containerId);
            containerTransition.firstOut = fragment;
            containerTransition.firstOutIsPop = isPop;
            containerTransition.firstOutTransaction = transaction;
        }

        if (!isReorderedTransaction && wasRemoved
                && (containerTransition != null && containerTransition.lastIn == fragment)) {
            containerTransition.lastIn = null;
        }
    }

    /**
     * Ensures that a FragmentContainerTransition has been added to the SparseArray. If so,
     * it returns the existing one. If not, one is created and added to the SparseArray and
     * returned.
     */
    private static FragmentContainerTransition ensureContainer(
            FragmentContainerTransition containerTransition,
            SparseArray<FragmentContainerTransition> transitioningFragments, int containerId) {
        if (containerTransition == null) {
            containerTransition = new FragmentContainerTransition();
            transitioningFragments.put(containerId, containerTransition);
        }
        return containerTransition;
    }

    /**
     * Tracks the last fragment added and first fragment removed for fragment transitions.
     * This also tracks which fragments are changed by push or pop transactions.
     */
    static class FragmentContainerTransition {
        /**
         * The last fragment added/attached/shown in its container
         */
        public Fragment lastIn;

        /**
         * true when lastIn was added during a pop transaction or false if added with a push
         */
        public boolean lastInIsPop;

        /**
         * The transaction that included the last in fragment
         */
        public BackStackRecord lastInTransaction;

        /**
         * The first fragment with a View that was removed/detached/hidden in its container.
         */
        public Fragment firstOut;

        /**
         * true when firstOut was removed during a pop transaction or false otherwise
         */
        public boolean firstOutIsPop;

        /**
         * The transaction that included the first out fragment
         */
        public BackStackRecord firstOutTransaction;
    }

    private FragmentTransition() {
    }
}