recyclerview/recyclerview/src/main/java/androidx/recyclerview/widget/DefaultItemAnimator.java - platform/frameworks/support - Git at Google

 /*
  * 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.recyclerview.widget;

 import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
 import android.animation.TimeInterpolator;
 import android.animation.ValueAnimator;
 import android.annotation.SuppressLint;
 import android.view.View;
 import android.view.ViewPropertyAnimator;

 import androidx.annotation.NonNull;
 import androidx.core.view.ViewCompat;

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

 /**
  * This implementation of {@link RecyclerView.ItemAnimator} provides basic
  * animations on remove, add, and move events that happen to the items in
  * a RecyclerView. RecyclerView uses a DefaultItemAnimator by default.
  *
  * @see RecyclerView#setItemAnimator(RecyclerView.ItemAnimator)
  */
 public class DefaultItemAnimator extends SimpleItemAnimator {
     private static final boolean DEBUG = false;

     private static TimeInterpolator sDefaultInterpolator;

     private ArrayList<RecyclerView.ViewHolder> mPendingRemovals = new ArrayList<>();
     private ArrayList<RecyclerView.ViewHolder> mPendingAdditions = new ArrayList<>();
     private ArrayList<MoveInfo> mPendingMoves = new ArrayList<>();
     private ArrayList<ChangeInfo> mPendingChanges = new ArrayList<>();

     ArrayList<ArrayList<RecyclerView.ViewHolder>> mAdditionsList = new ArrayList<>();
     ArrayList<ArrayList<MoveInfo>> mMovesList = new ArrayList<>();
     ArrayList<ArrayList<ChangeInfo>> mChangesList = new ArrayList<>();

     ArrayList<RecyclerView.ViewHolder> mAddAnimations = new ArrayList<>();
     ArrayList<RecyclerView.ViewHolder> mMoveAnimations = new ArrayList<>();
     ArrayList<RecyclerView.ViewHolder> mRemoveAnimations = new ArrayList<>();
     ArrayList<RecyclerView.ViewHolder> mChangeAnimations = new ArrayList<>();

     private static class MoveInfo {
         public RecyclerView.ViewHolder holder;
         public int fromX, fromY, toX, toY;

         MoveInfo(RecyclerView.ViewHolder holder, int fromX, int fromY, int toX, int toY) {
             this.holder = holder;
             this.fromX = fromX;
             this.fromY = fromY;
             this.toX = toX;
             this.toY = toY;
         }
     }

     private static class ChangeInfo {
         public RecyclerView.ViewHolder oldHolder, newHolder;
         public int fromX, fromY, toX, toY;
         private ChangeInfo(RecyclerView.ViewHolder oldHolder, RecyclerView.ViewHolder newHolder) {
             this.oldHolder = oldHolder;
             this.newHolder = newHolder;
         }

         ChangeInfo(RecyclerView.ViewHolder oldHolder, RecyclerView.ViewHolder newHolder,
                 int fromX, int fromY, int toX, int toY) {
             this(oldHolder, newHolder);
             this.fromX = fromX;
             this.fromY = fromY;
             this.toX = toX;
             this.toY = toY;
         }

         @Override
         @SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
         public String toString() {
             return "ChangeInfo{"
                     + "oldHolder=" + oldHolder
                     + ", newHolder=" + newHolder
                     + ", fromX=" + fromX
                     + ", fromY=" + fromY
                     + ", toX=" + toX
                     + ", toY=" + toY
                     + '}';
         }
     }

     @Override
     public void runPendingAnimations() {
         boolean removalsPending = !mPendingRemovals.isEmpty();
         boolean movesPending = !mPendingMoves.isEmpty();
         boolean changesPending = !mPendingChanges.isEmpty();
         boolean additionsPending = !mPendingAdditions.isEmpty();
         if (!removalsPending && !movesPending && !additionsPending && !changesPending) {
             // nothing to animate
             return;
         }
         // First, remove stuff
         for (RecyclerView.ViewHolder holder : mPendingRemovals) {
             animateRemoveImpl(holder);
         }
         mPendingRemovals.clear();
         // Next, move stuff
         if (movesPending) {
             final ArrayList<MoveInfo> moves = new ArrayList<>();
             moves.addAll(mPendingMoves);
             mMovesList.add(moves);
             mPendingMoves.clear();
             Runnable mover = new Runnable() {
                 @Override
                 public void run() {
                     for (MoveInfo moveInfo : moves) {
                         animateMoveImpl(moveInfo.holder, moveInfo.fromX, moveInfo.fromY,
                                 moveInfo.toX, moveInfo.toY);
                     }
                     moves.clear();
                     mMovesList.remove(moves);
                 }
             };
             if (removalsPending) {
                 View view = moves.get(0).holder.itemView;
                 ViewCompat.postOnAnimationDelayed(view, mover, getRemoveDuration());
             } else {
                 mover.run();
             }
         }
         // Next, change stuff, to run in parallel with move animations
         if (changesPending) {
             final ArrayList<ChangeInfo> changes = new ArrayList<>();
             changes.addAll(mPendingChanges);
             mChangesList.add(changes);
             mPendingChanges.clear();
             Runnable changer = new Runnable() {
                 @Override
                 public void run() {
                     for (ChangeInfo change : changes) {
                         animateChangeImpl(change);
                     }
                     changes.clear();
                     mChangesList.remove(changes);
                 }
             };
             if (removalsPending) {
                 RecyclerView.ViewHolder holder = changes.get(0).oldHolder;
                 ViewCompat.postOnAnimationDelayed(holder.itemView, changer, getRemoveDuration());
             } else {
                 changer.run();
             }
         }
         // Next, add stuff
         if (additionsPending) {
             final ArrayList<RecyclerView.ViewHolder> additions = new ArrayList<>();
             additions.addAll(mPendingAdditions);
             mAdditionsList.add(additions);
             mPendingAdditions.clear();
             Runnable adder = new Runnable() {
                 @Override
                 public void run() {
                     for (RecyclerView.ViewHolder holder : additions) {
                         animateAddImpl(holder);
                     }
                     additions.clear();
                     mAdditionsList.remove(additions);
                 }
             };
             if (removalsPending || movesPending || changesPending) {
                 long removeDuration = removalsPending ? getRemoveDuration() : 0;
                 long moveDuration = movesPending ? getMoveDuration() : 0;
                 long changeDuration = changesPending ? getChangeDuration() : 0;
                 long totalDelay = removeDuration + Math.max(moveDuration, changeDuration);
                 View view = additions.get(0).itemView;
                 ViewCompat.postOnAnimationDelayed(view, adder, totalDelay);
             } else {
                 adder.run();
             }
         }
     }

     @Override
     @SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
     public boolean animateRemove(final RecyclerView.ViewHolder holder) {
         resetAnimation(holder);
         mPendingRemovals.add(holder);
         return true;
     }

     private void animateRemoveImpl(final RecyclerView.ViewHolder holder) {
         final View view = holder.itemView;
         final ViewPropertyAnimator animation = view.animate();
         mRemoveAnimations.add(holder);
         animation.setDuration(getRemoveDuration()).alpha(0).setListener(
                 new AnimatorListenerAdapter() {
                     @Override
                     public void onAnimationStart(Animator animator) {
                         dispatchRemoveStarting(holder);
                     }

                     @Override
                     public void onAnimationEnd(Animator animator) {
                         animation.setListener(null);
                         view.setAlpha(1);
                         dispatchRemoveFinished(holder);
                         mRemoveAnimations.remove(holder);
                         dispatchFinishedWhenDone();
                     }
                 }).start();
     }

     @Override
     @SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
     public boolean animateAdd(final RecyclerView.ViewHolder holder) {
         resetAnimation(holder);
         holder.itemView.setAlpha(0);
         mPendingAdditions.add(holder);
         return true;
     }

     void animateAddImpl(final RecyclerView.ViewHolder holder) {
         final View view = holder.itemView;
         final ViewPropertyAnimator animation = view.animate();
         mAddAnimations.add(holder);
         animation.alpha(1).setDuration(getAddDuration())
                 .setListener(new AnimatorListenerAdapter() {
                     @Override
                     public void onAnimationStart(Animator animator) {
                         dispatchAddStarting(holder);
                     }

                     @Override
                     public void onAnimationCancel(Animator animator) {
                         view.setAlpha(1);
                     }

                     @Override
                     public void onAnimationEnd(Animator animator) {
                         animation.setListener(null);
                         dispatchAddFinished(holder);
                         mAddAnimations.remove(holder);
                         dispatchFinishedWhenDone();
                     }
                 }).start();
     }

     @Override
     @SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
     public boolean animateMove(final RecyclerView.ViewHolder holder, int fromX, int fromY,
             int toX, int toY) {
         final View view = holder.itemView;
         fromX += (int) holder.itemView.getTranslationX();
         fromY += (int) holder.itemView.getTranslationY();
         resetAnimation(holder);
         int deltaX = toX - fromX;
         int deltaY = toY - fromY;
         if (deltaX == 0 && deltaY == 0) {
             dispatchMoveFinished(holder);
             return false;
         }
         if (deltaX != 0) {
             view.setTranslationX(-deltaX);
         }
         if (deltaY != 0) {
             view.setTranslationY(-deltaY);
         }
         mPendingMoves.add(new MoveInfo(holder, fromX, fromY, toX, toY));
         return true;
     }

     void animateMoveImpl(final RecyclerView.ViewHolder holder, int fromX, int fromY, int toX, int toY) {
         final View view = holder.itemView;
         final int deltaX = toX - fromX;
         final int deltaY = toY - fromY;
         if (deltaX != 0) {
             view.animate().translationX(0);
         }
         if (deltaY != 0) {
             view.animate().translationY(0);
         }
         // TODO: make EndActions end listeners instead, since end actions aren't called when
         // vpas are canceled (and can't end them. why?)
         // need listener functionality in VPACompat for this. Ick.
         final ViewPropertyAnimator animation = view.animate();
         mMoveAnimations.add(holder);
         animation.setDuration(getMoveDuration()).setListener(new AnimatorListenerAdapter() {
             @Override
             public void onAnimationStart(Animator animator) {
                 dispatchMoveStarting(holder);
             }

             @Override
             public void onAnimationCancel(Animator animator) {
                 if (deltaX != 0) {
                     view.setTranslationX(0);
                 }
                 if (deltaY != 0) {
                     view.setTranslationY(0);
                 }
             }

             @Override
             public void onAnimationEnd(Animator animator) {
                 animation.setListener(null);
                 dispatchMoveFinished(holder);
                 mMoveAnimations.remove(holder);
                 dispatchFinishedWhenDone();
             }
         }).start();
     }

     @Override
     @SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
     public boolean animateChange(RecyclerView.ViewHolder oldHolder,
             RecyclerView.ViewHolder newHolder, int fromLeft, int fromTop, int toLeft, int toTop) {
         if (oldHolder == newHolder) {
             // Don't know how to run change animations when the same view holder is re-used.
             // run a move animation to handle position changes.
             return animateMove(oldHolder, fromLeft, fromTop, toLeft, toTop);
         }
         final float prevTranslationX = oldHolder.itemView.getTranslationX();
         final float prevTranslationY = oldHolder.itemView.getTranslationY();
         final float prevAlpha = oldHolder.itemView.getAlpha();
         resetAnimation(oldHolder);
         int deltaX = (int) (toLeft - fromLeft - prevTranslationX);
         int deltaY = (int) (toTop - fromTop - prevTranslationY);
         // recover prev translation state after ending animation
         oldHolder.itemView.setTranslationX(prevTranslationX);
         oldHolder.itemView.setTranslationY(prevTranslationY);
         oldHolder.itemView.setAlpha(prevAlpha);
         if (newHolder != null) {
             // carry over translation values
             resetAnimation(newHolder);
             newHolder.itemView.setTranslationX(-deltaX);
             newHolder.itemView.setTranslationY(-deltaY);
             newHolder.itemView.setAlpha(0);
         }
         mPendingChanges.add(new ChangeInfo(oldHolder, newHolder, fromLeft, fromTop, toLeft, toTop));
         return true;
     }

     void animateChangeImpl(final ChangeInfo changeInfo) {
         final RecyclerView.ViewHolder holder = changeInfo.oldHolder;
         final View view = holder == null ? null : holder.itemView;
         final RecyclerView.ViewHolder newHolder = changeInfo.newHolder;
         final View newView = newHolder != null ? newHolder.itemView : null;
         if (view != null) {
             final ViewPropertyAnimator oldViewAnim = view.animate().setDuration(
                     getChangeDuration());
             mChangeAnimations.add(changeInfo.oldHolder);
             oldViewAnim.translationX(changeInfo.toX - changeInfo.fromX);
             oldViewAnim.translationY(changeInfo.toY - changeInfo.fromY);
             oldViewAnim.alpha(0).setListener(new AnimatorListenerAdapter() {
                 @Override
                 public void onAnimationStart(Animator animator) {
                     dispatchChangeStarting(changeInfo.oldHolder, true);
                 }

                 @Override
                 public void onAnimationEnd(Animator animator) {
                     oldViewAnim.setListener(null);
                     view.setAlpha(1);
                     view.setTranslationX(0);
                     view.setTranslationY(0);
                     dispatchChangeFinished(changeInfo.oldHolder, true);
                     mChangeAnimations.remove(changeInfo.oldHolder);
                     dispatchFinishedWhenDone();
                 }
             }).start();
         }
         if (newView != null) {
             final ViewPropertyAnimator newViewAnimation = newView.animate();
             mChangeAnimations.add(changeInfo.newHolder);
             newViewAnimation.translationX(0).translationY(0).setDuration(getChangeDuration())
                     .alpha(1).setListener(new AnimatorListenerAdapter() {
                         @Override
                         public void onAnimationStart(Animator animator) {
                             dispatchChangeStarting(changeInfo.newHolder, false);
                         }
                         @Override
                         public void onAnimationEnd(Animator animator) {
                             newViewAnimation.setListener(null);
                             newView.setAlpha(1);
                             newView.setTranslationX(0);
                             newView.setTranslationY(0);
                             dispatchChangeFinished(changeInfo.newHolder, false);
                             mChangeAnimations.remove(changeInfo.newHolder);
                             dispatchFinishedWhenDone();
                         }
                     }).start();
         }
     }

     private void endChangeAnimation(List<ChangeInfo> infoList, RecyclerView.ViewHolder item) {
         for (int i = infoList.size() - 1; i >= 0; i--) {
             ChangeInfo changeInfo = infoList.get(i);
             if (endChangeAnimationIfNecessary(changeInfo, item)) {
                 if (changeInfo.oldHolder == null && changeInfo.newHolder == null) {
                     infoList.remove(changeInfo);
                 }
             }
         }
     }

     private void endChangeAnimationIfNecessary(ChangeInfo changeInfo) {
         if (changeInfo.oldHolder != null) {
             endChangeAnimationIfNecessary(changeInfo, changeInfo.oldHolder);
         }
         if (changeInfo.newHolder != null) {
             endChangeAnimationIfNecessary(changeInfo, changeInfo.newHolder);
         }
     }
     private boolean endChangeAnimationIfNecessary(ChangeInfo changeInfo, RecyclerView.ViewHolder item) {
         boolean oldItem = false;
         if (changeInfo.newHolder == item) {
             changeInfo.newHolder = null;
         } else if (changeInfo.oldHolder == item) {
             changeInfo.oldHolder = null;
             oldItem = true;
         } else {
             return false;
         }
         item.itemView.setAlpha(1);
         item.itemView.setTranslationX(0);
         item.itemView.setTranslationY(0);
         dispatchChangeFinished(item, oldItem);
         return true;
     }

     @Override
     @SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
     public void endAnimation(RecyclerView.ViewHolder item) {
         final View view = item.itemView;
         // this will trigger end callback which should set properties to their target values.
         view.animate().cancel();
         // TODO if some other animations are chained to end, how do we cancel them as well?
         for (int i = mPendingMoves.size() - 1; i >= 0; i--) {
             MoveInfo moveInfo = mPendingMoves.get(i);
             if (moveInfo.holder == item) {
                 view.setTranslationY(0);
                 view.setTranslationX(0);
                 dispatchMoveFinished(item);
                 mPendingMoves.remove(i);
             }
         }
         endChangeAnimation(mPendingChanges, item);
         if (mPendingRemovals.remove(item)) {
             view.setAlpha(1);
             dispatchRemoveFinished(item);
         }
         if (mPendingAdditions.remove(item)) {
             view.setAlpha(1);
             dispatchAddFinished(item);
         }

         for (int i = mChangesList.size() - 1; i >= 0; i--) {
             ArrayList<ChangeInfo> changes = mChangesList.get(i);
             endChangeAnimation(changes, item);
             if (changes.isEmpty()) {
                 mChangesList.remove(i);
             }
         }
         for (int i = mMovesList.size() - 1; i >= 0; i--) {
             ArrayList<MoveInfo> moves = mMovesList.get(i);
             for (int j = moves.size() - 1; j >= 0; j--) {
                 MoveInfo moveInfo = moves.get(j);
                 if (moveInfo.holder == item) {
                     view.setTranslationY(0);
                     view.setTranslationX(0);
                     dispatchMoveFinished(item);
                     moves.remove(j);
                     if (moves.isEmpty()) {
                         mMovesList.remove(i);
                     }
                     break;
                 }
             }
         }
         for (int i = mAdditionsList.size() - 1; i >= 0; i--) {
             ArrayList<RecyclerView.ViewHolder> additions = mAdditionsList.get(i);
             if (additions.remove(item)) {
                 view.setAlpha(1);
                 dispatchAddFinished(item);
                 if (additions.isEmpty()) {
                     mAdditionsList.remove(i);
                 }
             }
         }

         // animations should be ended by the cancel above.
         //noinspection PointlessBooleanExpression,ConstantConditions
         if (mRemoveAnimations.remove(item) && DEBUG) {
             throw new IllegalStateException("after animation is cancelled, item should not be in "
                     + "mRemoveAnimations list");
         }

         //noinspection PointlessBooleanExpression,ConstantConditions
         if (mAddAnimations.remove(item) && DEBUG) {
             throw new IllegalStateException("after animation is cancelled, item should not be in "
                     + "mAddAnimations list");
         }

         //noinspection PointlessBooleanExpression,ConstantConditions
         if (mChangeAnimations.remove(item) && DEBUG) {
             throw new IllegalStateException("after animation is cancelled, item should not be in "
                     + "mChangeAnimations list");
         }

         //noinspection PointlessBooleanExpression,ConstantConditions
         if (mMoveAnimations.remove(item) && DEBUG) {
             throw new IllegalStateException("after animation is cancelled, item should not be in "
                     + "mMoveAnimations list");
         }
         dispatchFinishedWhenDone();
     }

     private void resetAnimation(RecyclerView.ViewHolder holder) {
         if (sDefaultInterpolator == null) {
             sDefaultInterpolator = new ValueAnimator().getInterpolator();
         }
         holder.itemView.animate().setInterpolator(sDefaultInterpolator);
         endAnimation(holder);
     }

     @Override
     public boolean isRunning() {
         return (!mPendingAdditions.isEmpty()
                 || !mPendingChanges.isEmpty()
                 || !mPendingMoves.isEmpty()
                 || !mPendingRemovals.isEmpty()
                 || !mMoveAnimations.isEmpty()
                 || !mRemoveAnimations.isEmpty()
                 || !mAddAnimations.isEmpty()
                 || !mChangeAnimations.isEmpty()
                 || !mMovesList.isEmpty()
                 || !mAdditionsList.isEmpty()
                 || !mChangesList.isEmpty());
     }

     /**
      * Check the state of currently pending and running animations. If there are none
      * pending/running, call {@link #dispatchAnimationsFinished()} to notify any
      * listeners.
      */
     void dispatchFinishedWhenDone() {
         if (!isRunning()) {
             dispatchAnimationsFinished();
         }
     }

     @Override
     public void endAnimations() {
         int count = mPendingMoves.size();
         for (int i = count - 1; i >= 0; i--) {
             MoveInfo item = mPendingMoves.get(i);
             View view = item.holder.itemView;
             view.setTranslationY(0);
             view.setTranslationX(0);
             dispatchMoveFinished(item.holder);
             mPendingMoves.remove(i);
         }
         count = mPendingRemovals.size();
         for (int i = count - 1; i >= 0; i--) {
             RecyclerView.ViewHolder item = mPendingRemovals.get(i);
             dispatchRemoveFinished(item);
             mPendingRemovals.remove(i);
         }
         count = mPendingAdditions.size();
         for (int i = count - 1; i >= 0; i--) {
             RecyclerView.ViewHolder item = mPendingAdditions.get(i);
             item.itemView.setAlpha(1);
             dispatchAddFinished(item);
             mPendingAdditions.remove(i);
         }
         count = mPendingChanges.size();
         for (int i = count - 1; i >= 0; i--) {
             endChangeAnimationIfNecessary(mPendingChanges.get(i));
         }
         mPendingChanges.clear();
         if (!isRunning()) {
             return;
         }

         int listCount = mMovesList.size();
         for (int i = listCount - 1; i >= 0; i--) {
             ArrayList<MoveInfo> moves = mMovesList.get(i);
             count = moves.size();
             for (int j = count - 1; j >= 0; j--) {
                 MoveInfo moveInfo = moves.get(j);
                 RecyclerView.ViewHolder item = moveInfo.holder;
                 View view = item.itemView;
                 view.setTranslationY(0);
                 view.setTranslationX(0);
                 dispatchMoveFinished(moveInfo.holder);
                 moves.remove(j);
                 if (moves.isEmpty()) {
                     mMovesList.remove(moves);
                 }
             }
         }
         listCount = mAdditionsList.size();
         for (int i = listCount - 1; i >= 0; i--) {
             ArrayList<RecyclerView.ViewHolder> additions = mAdditionsList.get(i);
             count = additions.size();
             for (int j = count - 1; j >= 0; j--) {
                 RecyclerView.ViewHolder item = additions.get(j);
                 View view = item.itemView;
                 view.setAlpha(1);
                 dispatchAddFinished(item);
                 additions.remove(j);
                 if (additions.isEmpty()) {
                     mAdditionsList.remove(additions);
                 }
             }
         }
         listCount = mChangesList.size();
         for (int i = listCount - 1; i >= 0; i--) {
             ArrayList<ChangeInfo> changes = mChangesList.get(i);
             count = changes.size();
             for (int j = count - 1; j >= 0; j--) {
                 endChangeAnimationIfNecessary(changes.get(j));
                 if (changes.isEmpty()) {
                     mChangesList.remove(changes);
                 }
             }
         }

         cancelAll(mRemoveAnimations);
         cancelAll(mMoveAnimations);
         cancelAll(mAddAnimations);
         cancelAll(mChangeAnimations);

         dispatchAnimationsFinished();
     }

     void cancelAll(List<RecyclerView.ViewHolder> viewHolders) {
         for (int i = viewHolders.size() - 1; i >= 0; i--) {
             viewHolders.get(i).itemView.animate().cancel();
         }
     }

     /**
      * {@inheritDoc}
      * <p>
      * If the payload list is not empty, DefaultItemAnimator returns <code>true</code>.
      * When this is the case:
      * <ul>
      * <li>If you override {@link #animateChange(RecyclerView.ViewHolder, RecyclerView.ViewHolder, int, int, int, int)}, both
      * ViewHolder arguments will be the same instance.
      * </li>
      * <li>
      * If you are not overriding {@link #animateChange(RecyclerView.ViewHolder, RecyclerView.ViewHolder, int, int, int, int)},
      * then DefaultItemAnimator will call {@link #animateMove(RecyclerView.ViewHolder, int, int, int, int)} and
      * run a move animation instead.
      * </li>
      * </ul>
      */
     @Override
     public boolean canReuseUpdatedViewHolder(@NonNull RecyclerView.ViewHolder viewHolder,
             @NonNull List<Object> payloads) {
         return !payloads.isEmpty() || super.canReuseUpdatedViewHolder(viewHolder, payloads);
     }
 }
	/*
	* 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.recyclerview.widget;

	import android.animation.Animator;
	import android.animation.AnimatorListenerAdapter;
	import android.animation.TimeInterpolator;
	import android.animation.ValueAnimator;
	import android.annotation.SuppressLint;
	import android.view.View;
	import android.view.ViewPropertyAnimator;

	import androidx.annotation.NonNull;
	import androidx.core.view.ViewCompat;

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

	/**
	* This implementation of {@link RecyclerView.ItemAnimator} provides basic
	* animations on remove, add, and move events that happen to the items in
	* a RecyclerView. RecyclerView uses a DefaultItemAnimator by default.
	*
	* @see RecyclerView#setItemAnimator(RecyclerView.ItemAnimator)
	*/
	public class DefaultItemAnimator extends SimpleItemAnimator {
	private static final boolean DEBUG = false;

	private static TimeInterpolator sDefaultInterpolator;

	private ArrayList<RecyclerView.ViewHolder> mPendingRemovals = new ArrayList<>();
	private ArrayList<RecyclerView.ViewHolder> mPendingAdditions = new ArrayList<>();
	private ArrayList<MoveInfo> mPendingMoves = new ArrayList<>();
	private ArrayList<ChangeInfo> mPendingChanges = new ArrayList<>();

	ArrayList<ArrayList<RecyclerView.ViewHolder>> mAdditionsList = new ArrayList<>();
	ArrayList<ArrayList<MoveInfo>> mMovesList = new ArrayList<>();
	ArrayList<ArrayList<ChangeInfo>> mChangesList = new ArrayList<>();

	ArrayList<RecyclerView.ViewHolder> mAddAnimations = new ArrayList<>();
	ArrayList<RecyclerView.ViewHolder> mMoveAnimations = new ArrayList<>();
	ArrayList<RecyclerView.ViewHolder> mRemoveAnimations = new ArrayList<>();
	ArrayList<RecyclerView.ViewHolder> mChangeAnimations = new ArrayList<>();

	private static class MoveInfo {
	public RecyclerView.ViewHolder holder;
	public int fromX, fromY, toX, toY;

	MoveInfo(RecyclerView.ViewHolder holder, int fromX, int fromY, int toX, int toY) {
	this.holder = holder;
	this.fromX = fromX;
	this.fromY = fromY;
	this.toX = toX;
	this.toY = toY;
	}
	}

	private static class ChangeInfo {
	public RecyclerView.ViewHolder oldHolder, newHolder;
	public int fromX, fromY, toX, toY;
	private ChangeInfo(RecyclerView.ViewHolder oldHolder, RecyclerView.ViewHolder newHolder) {
	this.oldHolder = oldHolder;
	this.newHolder = newHolder;
	}

	ChangeInfo(RecyclerView.ViewHolder oldHolder, RecyclerView.ViewHolder newHolder,
	int fromX, int fromY, int toX, int toY) {
	this(oldHolder, newHolder);
	this.fromX = fromX;
	this.fromY = fromY;
	this.toX = toX;
	this.toY = toY;
	}

	@Override
	@SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
	public String toString() {
	return "ChangeInfo{"
	+ "oldHolder=" + oldHolder
	+ ", newHolder=" + newHolder
	+ ", fromX=" + fromX
	+ ", fromY=" + fromY
	+ ", toX=" + toX
	+ ", toY=" + toY
	+ '}';
	}
	}

	@Override
	public void runPendingAnimations() {
	boolean removalsPending = !mPendingRemovals.isEmpty();
	boolean movesPending = !mPendingMoves.isEmpty();
	boolean changesPending = !mPendingChanges.isEmpty();
	boolean additionsPending = !mPendingAdditions.isEmpty();
	if (!removalsPending && !movesPending && !additionsPending && !changesPending) {
	// nothing to animate
	return;
	}
	// First, remove stuff
	for (RecyclerView.ViewHolder holder : mPendingRemovals) {
	animateRemoveImpl(holder);
	}
	mPendingRemovals.clear();
	// Next, move stuff
	if (movesPending) {
	final ArrayList<MoveInfo> moves = new ArrayList<>();
	moves.addAll(mPendingMoves);
	mMovesList.add(moves);
	mPendingMoves.clear();
	Runnable mover = new Runnable() {
	@Override
	public void run() {
	for (MoveInfo moveInfo : moves) {
	animateMoveImpl(moveInfo.holder, moveInfo.fromX, moveInfo.fromY,
	moveInfo.toX, moveInfo.toY);
	}
	moves.clear();
	mMovesList.remove(moves);
	}
	};
	if (removalsPending) {
	View view = moves.get(0).holder.itemView;
	ViewCompat.postOnAnimationDelayed(view, mover, getRemoveDuration());
	} else {
	mover.run();
	}
	}
	// Next, change stuff, to run in parallel with move animations
	if (changesPending) {
	final ArrayList<ChangeInfo> changes = new ArrayList<>();
	changes.addAll(mPendingChanges);
	mChangesList.add(changes);
	mPendingChanges.clear();
	Runnable changer = new Runnable() {
	@Override
	public void run() {
	for (ChangeInfo change : changes) {
	animateChangeImpl(change);
	}
	changes.clear();
	mChangesList.remove(changes);
	}
	};
	if (removalsPending) {
	RecyclerView.ViewHolder holder = changes.get(0).oldHolder;
	ViewCompat.postOnAnimationDelayed(holder.itemView, changer, getRemoveDuration());
	} else {
	changer.run();
	}
	}
	// Next, add stuff
	if (additionsPending) {
	final ArrayList<RecyclerView.ViewHolder> additions = new ArrayList<>();
	additions.addAll(mPendingAdditions);
	mAdditionsList.add(additions);
	mPendingAdditions.clear();
	Runnable adder = new Runnable() {
	@Override
	public void run() {
	for (RecyclerView.ViewHolder holder : additions) {
	animateAddImpl(holder);
	}
	additions.clear();
	mAdditionsList.remove(additions);
	}
	};
	if (removalsPending \|\| movesPending \|\| changesPending) {
	long removeDuration = removalsPending ? getRemoveDuration() : 0;
	long moveDuration = movesPending ? getMoveDuration() : 0;
	long changeDuration = changesPending ? getChangeDuration() : 0;
	long totalDelay = removeDuration + Math.max(moveDuration, changeDuration);
	View view = additions.get(0).itemView;
	ViewCompat.postOnAnimationDelayed(view, adder, totalDelay);
	} else {
	adder.run();
	}
	}
	}

	@Override
	@SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
	public boolean animateRemove(final RecyclerView.ViewHolder holder) {
	resetAnimation(holder);
	mPendingRemovals.add(holder);
	return true;
	}

	private void animateRemoveImpl(final RecyclerView.ViewHolder holder) {
	final View view = holder.itemView;
	final ViewPropertyAnimator animation = view.animate();
	mRemoveAnimations.add(holder);
	animation.setDuration(getRemoveDuration()).alpha(0).setListener(
	new AnimatorListenerAdapter() {
	@Override
	public void onAnimationStart(Animator animator) {
	dispatchRemoveStarting(holder);
	}

	@Override
	public void onAnimationEnd(Animator animator) {
	animation.setListener(null);
	view.setAlpha(1);
	dispatchRemoveFinished(holder);
	mRemoveAnimations.remove(holder);
	dispatchFinishedWhenDone();
	}
	}).start();
	}

	@Override
	@SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
	public boolean animateAdd(final RecyclerView.ViewHolder holder) {
	resetAnimation(holder);
	holder.itemView.setAlpha(0);
	mPendingAdditions.add(holder);
	return true;
	}

	void animateAddImpl(final RecyclerView.ViewHolder holder) {
	final View view = holder.itemView;
	final ViewPropertyAnimator animation = view.animate();
	mAddAnimations.add(holder);
	animation.alpha(1).setDuration(getAddDuration())
	.setListener(new AnimatorListenerAdapter() {
	@Override
	public void onAnimationStart(Animator animator) {
	dispatchAddStarting(holder);
	}

	@Override
	public void onAnimationCancel(Animator animator) {
	view.setAlpha(1);
	}

	@Override
	public void onAnimationEnd(Animator animator) {
	animation.setListener(null);
	dispatchAddFinished(holder);
	mAddAnimations.remove(holder);
	dispatchFinishedWhenDone();
	}
	}).start();
	}

	@Override
	@SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
	public boolean animateMove(final RecyclerView.ViewHolder holder, int fromX, int fromY,
	int toX, int toY) {
	final View view = holder.itemView;
	fromX += (int) holder.itemView.getTranslationX();
	fromY += (int) holder.itemView.getTranslationY();
	resetAnimation(holder);
	int deltaX = toX - fromX;
	int deltaY = toY - fromY;
	if (deltaX == 0 && deltaY == 0) {
	dispatchMoveFinished(holder);
	return false;
	}
	if (deltaX != 0) {
	view.setTranslationX(-deltaX);
	}
	if (deltaY != 0) {
	view.setTranslationY(-deltaY);
	}
	mPendingMoves.add(new MoveInfo(holder, fromX, fromY, toX, toY));
	return true;
	}

	void animateMoveImpl(final RecyclerView.ViewHolder holder, int fromX, int fromY, int toX, int toY) {
	final View view = holder.itemView;
	final int deltaX = toX - fromX;
	final int deltaY = toY - fromY;
	if (deltaX != 0) {
	view.animate().translationX(0);
	}
	if (deltaY != 0) {
	view.animate().translationY(0);
	}
	// TODO: make EndActions end listeners instead, since end actions aren't called when
	// vpas are canceled (and can't end them. why?)
	// need listener functionality in VPACompat for this. Ick.
	final ViewPropertyAnimator animation = view.animate();
	mMoveAnimations.add(holder);
	animation.setDuration(getMoveDuration()).setListener(new AnimatorListenerAdapter() {
	@Override
	public void onAnimationStart(Animator animator) {
	dispatchMoveStarting(holder);
	}

	@Override
	public void onAnimationCancel(Animator animator) {
	if (deltaX != 0) {
	view.setTranslationX(0);
	}
	if (deltaY != 0) {
	view.setTranslationY(0);
	}
	}

	@Override
	public void onAnimationEnd(Animator animator) {
	animation.setListener(null);
	dispatchMoveFinished(holder);
	mMoveAnimations.remove(holder);
	dispatchFinishedWhenDone();
	}
	}).start();
	}

	@Override
	@SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
	public boolean animateChange(RecyclerView.ViewHolder oldHolder,
	RecyclerView.ViewHolder newHolder, int fromLeft, int fromTop, int toLeft, int toTop) {
	if (oldHolder == newHolder) {
	// Don't know how to run change animations when the same view holder is re-used.
	// run a move animation to handle position changes.
	return animateMove(oldHolder, fromLeft, fromTop, toLeft, toTop);
	}
	final float prevTranslationX = oldHolder.itemView.getTranslationX();
	final float prevTranslationY = oldHolder.itemView.getTranslationY();
	final float prevAlpha = oldHolder.itemView.getAlpha();
	resetAnimation(oldHolder);
	int deltaX = (int) (toLeft - fromLeft - prevTranslationX);
	int deltaY = (int) (toTop - fromTop - prevTranslationY);
	// recover prev translation state after ending animation
	oldHolder.itemView.setTranslationX(prevTranslationX);
	oldHolder.itemView.setTranslationY(prevTranslationY);
	oldHolder.itemView.setAlpha(prevAlpha);
	if (newHolder != null) {
	// carry over translation values
	resetAnimation(newHolder);
	newHolder.itemView.setTranslationX(-deltaX);
	newHolder.itemView.setTranslationY(-deltaY);
	newHolder.itemView.setAlpha(0);
	}
	mPendingChanges.add(new ChangeInfo(oldHolder, newHolder, fromLeft, fromTop, toLeft, toTop));
	return true;
	}

	void animateChangeImpl(final ChangeInfo changeInfo) {
	final RecyclerView.ViewHolder holder = changeInfo.oldHolder;
	final View view = holder == null ? null : holder.itemView;
	final RecyclerView.ViewHolder newHolder = changeInfo.newHolder;
	final View newView = newHolder != null ? newHolder.itemView : null;
	if (view != null) {
	final ViewPropertyAnimator oldViewAnim = view.animate().setDuration(
	getChangeDuration());
	mChangeAnimations.add(changeInfo.oldHolder);
	oldViewAnim.translationX(changeInfo.toX - changeInfo.fromX);
	oldViewAnim.translationY(changeInfo.toY - changeInfo.fromY);
	oldViewAnim.alpha(0).setListener(new AnimatorListenerAdapter() {
	@Override
	public void onAnimationStart(Animator animator) {
	dispatchChangeStarting(changeInfo.oldHolder, true);
	}

	@Override
	public void onAnimationEnd(Animator animator) {
	oldViewAnim.setListener(null);
	view.setAlpha(1);
	view.setTranslationX(0);
	view.setTranslationY(0);
	dispatchChangeFinished(changeInfo.oldHolder, true);
	mChangeAnimations.remove(changeInfo.oldHolder);
	dispatchFinishedWhenDone();
	}
	}).start();
	}
	if (newView != null) {
	final ViewPropertyAnimator newViewAnimation = newView.animate();
	mChangeAnimations.add(changeInfo.newHolder);
	newViewAnimation.translationX(0).translationY(0).setDuration(getChangeDuration())
	.alpha(1).setListener(new AnimatorListenerAdapter() {
	@Override
	public void onAnimationStart(Animator animator) {
	dispatchChangeStarting(changeInfo.newHolder, false);
	}
	@Override
	public void onAnimationEnd(Animator animator) {
	newViewAnimation.setListener(null);
	newView.setAlpha(1);
	newView.setTranslationX(0);
	newView.setTranslationY(0);
	dispatchChangeFinished(changeInfo.newHolder, false);
	mChangeAnimations.remove(changeInfo.newHolder);
	dispatchFinishedWhenDone();
	}
	}).start();
	}
	}

	private void endChangeAnimation(List<ChangeInfo> infoList, RecyclerView.ViewHolder item) {
	for (int i = infoList.size() - 1; i >= 0; i--) {
	ChangeInfo changeInfo = infoList.get(i);
	if (endChangeAnimationIfNecessary(changeInfo, item)) {
	if (changeInfo.oldHolder == null && changeInfo.newHolder == null) {
	infoList.remove(changeInfo);
	}
	}
	}
	}

	private void endChangeAnimationIfNecessary(ChangeInfo changeInfo) {
	if (changeInfo.oldHolder != null) {
	endChangeAnimationIfNecessary(changeInfo, changeInfo.oldHolder);
	}
	if (changeInfo.newHolder != null) {
	endChangeAnimationIfNecessary(changeInfo, changeInfo.newHolder);
	}
	}
	private boolean endChangeAnimationIfNecessary(ChangeInfo changeInfo, RecyclerView.ViewHolder item) {
	boolean oldItem = false;
	if (changeInfo.newHolder == item) {
	changeInfo.newHolder = null;
	} else if (changeInfo.oldHolder == item) {
	changeInfo.oldHolder = null;
	oldItem = true;
	} else {
	return false;
	}
	item.itemView.setAlpha(1);
	item.itemView.setTranslationX(0);
	item.itemView.setTranslationY(0);
	dispatchChangeFinished(item, oldItem);
	return true;
	}

	@Override
	@SuppressLint("UnknownNullness") // b/240775049: Cannot annotate properly
	public void endAnimation(RecyclerView.ViewHolder item) {
	final View view = item.itemView;
	// this will trigger end callback which should set properties to their target values.
	view.animate().cancel();
	// TODO if some other animations are chained to end, how do we cancel them as well?
	for (int i = mPendingMoves.size() - 1; i >= 0; i--) {
	MoveInfo moveInfo = mPendingMoves.get(i);
	if (moveInfo.holder == item) {
	view.setTranslationY(0);
	view.setTranslationX(0);
	dispatchMoveFinished(item);
	mPendingMoves.remove(i);
	}
	}
	endChangeAnimation(mPendingChanges, item);
	if (mPendingRemovals.remove(item)) {
	view.setAlpha(1);
	dispatchRemoveFinished(item);
	}
	if (mPendingAdditions.remove(item)) {
	view.setAlpha(1);
	dispatchAddFinished(item);
	}

	for (int i = mChangesList.size() - 1; i >= 0; i--) {
	ArrayList<ChangeInfo> changes = mChangesList.get(i);
	endChangeAnimation(changes, item);
	if (changes.isEmpty()) {
	mChangesList.remove(i);
	}
	}
	for (int i = mMovesList.size() - 1; i >= 0; i--) {
	ArrayList<MoveInfo> moves = mMovesList.get(i);
	for (int j = moves.size() - 1; j >= 0; j--) {
	MoveInfo moveInfo = moves.get(j);
	if (moveInfo.holder == item) {
	view.setTranslationY(0);
	view.setTranslationX(0);
	dispatchMoveFinished(item);
	moves.remove(j);
	if (moves.isEmpty()) {
	mMovesList.remove(i);
	}
	break;
	}
	}
	}
	for (int i = mAdditionsList.size() - 1; i >= 0; i--) {
	ArrayList<RecyclerView.ViewHolder> additions = mAdditionsList.get(i);
	if (additions.remove(item)) {
	view.setAlpha(1);
	dispatchAddFinished(item);
	if (additions.isEmpty()) {
	mAdditionsList.remove(i);
	}
	}
	}

	// animations should be ended by the cancel above.
	//noinspection PointlessBooleanExpression,ConstantConditions
	if (mRemoveAnimations.remove(item) && DEBUG) {
	throw new IllegalStateException("after animation is cancelled, item should not be in "
	+ "mRemoveAnimations list");
	}

	//noinspection PointlessBooleanExpression,ConstantConditions
	if (mAddAnimations.remove(item) && DEBUG) {
	throw new IllegalStateException("after animation is cancelled, item should not be in "
	+ "mAddAnimations list");
	}

	//noinspection PointlessBooleanExpression,ConstantConditions
	if (mChangeAnimations.remove(item) && DEBUG) {
	throw new IllegalStateException("after animation is cancelled, item should not be in "
	+ "mChangeAnimations list");
	}

	//noinspection PointlessBooleanExpression,ConstantConditions
	if (mMoveAnimations.remove(item) && DEBUG) {
	throw new IllegalStateException("after animation is cancelled, item should not be in "
	+ "mMoveAnimations list");
	}
	dispatchFinishedWhenDone();
	}

	private void resetAnimation(RecyclerView.ViewHolder holder) {
	if (sDefaultInterpolator == null) {
	sDefaultInterpolator = new ValueAnimator().getInterpolator();
	}
	holder.itemView.animate().setInterpolator(sDefaultInterpolator);
	endAnimation(holder);
	}

	@Override
	public boolean isRunning() {
	return (!mPendingAdditions.isEmpty()
	\|\| !mPendingChanges.isEmpty()
	\|\| !mPendingMoves.isEmpty()
	\|\| !mPendingRemovals.isEmpty()
	\|\| !mMoveAnimations.isEmpty()
	\|\| !mRemoveAnimations.isEmpty()
	\|\| !mAddAnimations.isEmpty()
	\|\| !mChangeAnimations.isEmpty()
	\|\| !mMovesList.isEmpty()
	\|\| !mAdditionsList.isEmpty()
	\|\| !mChangesList.isEmpty());
	}

	/**
	* Check the state of currently pending and running animations. If there are none
	* pending/running, call {@link #dispatchAnimationsFinished()} to notify any
	* listeners.
	*/
	void dispatchFinishedWhenDone() {
	if (!isRunning()) {
	dispatchAnimationsFinished();
	}
	}

	@Override
	public void endAnimations() {
	int count = mPendingMoves.size();
	for (int i = count - 1; i >= 0; i--) {
	MoveInfo item = mPendingMoves.get(i);
	View view = item.holder.itemView;
	view.setTranslationY(0);
	view.setTranslationX(0);
	dispatchMoveFinished(item.holder);
	mPendingMoves.remove(i);
	}
	count = mPendingRemovals.size();
	for (int i = count - 1; i >= 0; i--) {
	RecyclerView.ViewHolder item = mPendingRemovals.get(i);
	dispatchRemoveFinished(item);
	mPendingRemovals.remove(i);
	}
	count = mPendingAdditions.size();
	for (int i = count - 1; i >= 0; i--) {
	RecyclerView.ViewHolder item = mPendingAdditions.get(i);
	item.itemView.setAlpha(1);
	dispatchAddFinished(item);
	mPendingAdditions.remove(i);
	}
	count = mPendingChanges.size();
	for (int i = count - 1; i >= 0; i--) {
	endChangeAnimationIfNecessary(mPendingChanges.get(i));
	}
	mPendingChanges.clear();
	if (!isRunning()) {
	return;
	}

	int listCount = mMovesList.size();
	for (int i = listCount - 1; i >= 0; i--) {
	ArrayList<MoveInfo> moves = mMovesList.get(i);
	count = moves.size();
	for (int j = count - 1; j >= 0; j--) {
	MoveInfo moveInfo = moves.get(j);
	RecyclerView.ViewHolder item = moveInfo.holder;
	View view = item.itemView;
	view.setTranslationY(0);
	view.setTranslationX(0);
	dispatchMoveFinished(moveInfo.holder);
	moves.remove(j);
	if (moves.isEmpty()) {
	mMovesList.remove(moves);
	}
	}
	}
	listCount = mAdditionsList.size();
	for (int i = listCount - 1; i >= 0; i--) {
	ArrayList<RecyclerView.ViewHolder> additions = mAdditionsList.get(i);
	count = additions.size();
	for (int j = count - 1; j >= 0; j--) {
	RecyclerView.ViewHolder item = additions.get(j);
	View view = item.itemView;
	view.setAlpha(1);
	dispatchAddFinished(item);
	additions.remove(j);
	if (additions.isEmpty()) {
	mAdditionsList.remove(additions);
	}
	}
	}
	listCount = mChangesList.size();
	for (int i = listCount - 1; i >= 0; i--) {
	ArrayList<ChangeInfo> changes = mChangesList.get(i);
	count = changes.size();
	for (int j = count - 1; j >= 0; j--) {
	endChangeAnimationIfNecessary(changes.get(j));
	if (changes.isEmpty()) {
	mChangesList.remove(changes);
	}
	}
	}

	cancelAll(mRemoveAnimations);
	cancelAll(mMoveAnimations);
	cancelAll(mAddAnimations);
	cancelAll(mChangeAnimations);

	dispatchAnimationsFinished();
	}

	void cancelAll(List<RecyclerView.ViewHolder> viewHolders) {
	for (int i = viewHolders.size() - 1; i >= 0; i--) {
	viewHolders.get(i).itemView.animate().cancel();
	}
	}

	/**
	* {@inheritDoc}
	* <p>
	* If the payload list is not empty, DefaultItemAnimator returns <code>true</code>.
	* When this is the case:
	* <ul>
	* <li>If you override {@link #animateChange(RecyclerView.ViewHolder, RecyclerView.ViewHolder, int, int, int, int)}, both
	* ViewHolder arguments will be the same instance.
	* </li>
	* <li>
	* If you are not overriding {@link #animateChange(RecyclerView.ViewHolder, RecyclerView.ViewHolder, int, int, int, int)},
	* then DefaultItemAnimator will call {@link #animateMove(RecyclerView.ViewHolder, int, int, int, int)} and
	* run a move animation instead.
	* </li>
	* </ul>
	*/
	@Override
	public boolean canReuseUpdatedViewHolder(@NonNull RecyclerView.ViewHolder viewHolder,
	@NonNull List<Object> payloads) {
	return !payloads.isEmpty() \|\| super.canReuseUpdatedViewHolder(viewHolder, payloads);
	}
	}