recyclerview/widget/ViewInfoStore.java

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package android.support.v7.widget;

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.annotation.VisibleForTesting;
import android.support.v4.util.ArrayMap;
import android.support.v4.util.LongSparseArray;
import android.support.v4.util.Pools;

import static android.support.v7.widget.RecyclerView.ViewHolder;
import static android.support.v7.widget.RecyclerView.ItemAnimator.ItemHolderInfo;

import static android.support.v7.widget.ViewInfoStore.InfoRecord.FLAG_APPEAR_PRE_AND_POST;
import static android.support.v7.widget.ViewInfoStore.InfoRecord.FLAG_APPEAR_AND_DISAPPEAR;
import static android.support.v7.widget.ViewInfoStore.InfoRecord.FLAG_PRE_AND_POST;
import static android.support.v7.widget.ViewInfoStore.InfoRecord.FLAG_DISAPPEARED;
import static android.support.v7.widget.ViewInfoStore.InfoRecord.FLAG_APPEAR;
import static android.support.v7.widget.ViewInfoStore.InfoRecord.FLAG_PRE;
import static android.support.v7.widget.ViewInfoStore.InfoRecord.FLAG_POST;
/**
 * This class abstracts all tracking for Views to run animations
 *
 * @hide
 */
class ViewInfoStore {

    private static final boolean DEBUG = false;

    /**
     * View data records for pre-layout
     */
    @VisibleForTesting
    final ArrayMap<ViewHolder, InfoRecord> mLayoutHolderMap = new ArrayMap<>();

    @VisibleForTesting
    final LongSparseArray<ViewHolder> mOldChangedHolders = new LongSparseArray<>();

    /**
     * Clears the state and all existing tracking data
     */
    void clear() {
        mLayoutHolderMap.clear();
        mOldChangedHolders.clear();
    }

    /**
     * Adds the item information to the prelayout tracking
     * @param holder The ViewHolder whose information is being saved
     * @param info The information to save
     */
    void addToPreLayout(ViewHolder holder, ItemHolderInfo info) {
        InfoRecord record = mLayoutHolderMap.get(holder);
        if (record == null) {
            record = InfoRecord.obtain();
            mLayoutHolderMap.put(holder, record);
        }
        record.preInfo = info;
        record.flags |= FLAG_PRE;
    }

    /**
     * Finds the ItemHolderInfo for the given ViewHolder in preLayout list and removes it.
     * @param vh The ViewHolder whose information is being queried
     * @return The ItemHolderInfo for the given ViewHolder or null if it does not exist
     */
    @Nullable
    ItemHolderInfo popFromPreLayout(ViewHolder vh) {
        int index = mLayoutHolderMap.indexOfKey(vh);
        if (index < 0) {
            return null;
        }
        final InfoRecord record = mLayoutHolderMap.valueAt(index);
        if (record != null && (record.flags & FLAG_PRE) != 0) {
            record.flags &= ~FLAG_PRE;
            final ItemHolderInfo info = record.preInfo;
            if (record.flags == 0) {
                mLayoutHolderMap.removeAt(index);
                InfoRecord.recycle(record);
            }
            return info;
        }
        return null;
    }

    /**
     * Adds the given ViewHolder to the oldChangeHolders list
     * @param key The key to identify the ViewHolder.
     * @param holder The ViewHolder to store
     */
    void addToOldChangeHolders(long key, ViewHolder holder) {
        mOldChangedHolders.put(key, holder);
    }

    /**
     * Adds the given ViewHolder to the appeared in pre layout list. These are Views added by the
     * LayoutManager during a pre-layout pass. We distinguish them from other views that were
     * already in the pre-layout so that ItemAnimator can choose to run a different animation for
     * them.
     *
     * @param holder The ViewHolder to store
     * @param info The information to save
     */
    void addToAppearedInPreLayoutHolders(ViewHolder holder, ItemHolderInfo info) {
        InfoRecord record = mLayoutHolderMap.get(holder);
        if (record == null) {
            record = InfoRecord.obtain();
            mLayoutHolderMap.put(holder, record);
        }
        record.flags |= FLAG_APPEAR;
        record.preInfo = info;
    }

    /**
     * Checks whether the given ViewHolder is in preLayout list
     * @param viewHolder The ViewHolder to query
     *
     * @return True if the ViewHolder is present in preLayout, false otherwise
     */
    boolean isInPreLayout(ViewHolder viewHolder) {
        final InfoRecord record = mLayoutHolderMap.get(viewHolder);
        return record != null && (record.flags & FLAG_PRE) != 0;
    }

    /**
     * Queries the oldChangeHolder list for the given key. If they are not tracked, simply returns
     * null.
     * @param key The key to be used to find the ViewHolder.
     *
     * @return A ViewHolder if exists or null if it does not exist.
     */
    ViewHolder getFromOldChangeHolders(long key) {
        return mOldChangedHolders.get(key);
    }

    /**
     * Adds the item information to the post layout list
     * @param holder The ViewHolder whose information is being saved
     * @param info The information to save
     */
    void addToPostLayout(ViewHolder holder, ItemHolderInfo info) {
        InfoRecord record = mLayoutHolderMap.get(holder);
        if (record == null) {
            record = InfoRecord.obtain();
            mLayoutHolderMap.put(holder, record);
        }
        record.postInfo = info;
        record.flags |= FLAG_POST;
    }

    /**
     * A ViewHolder might be added by the LayoutManager just to animate its disappearance.
     * This list holds such items so that we can animate / recycle these ViewHolders properly.
     *
     * @param holder The ViewHolder which disappeared during a layout.
     */
    void addToDisappearedInLayout(ViewHolder holder) {
        InfoRecord record = mLayoutHolderMap.get(holder);
        if (record == null) {
            record = InfoRecord.obtain();
            mLayoutHolderMap.put(holder, record);
        }
        record.flags |= FLAG_DISAPPEARED;
    }

    /**
     * Removes a ViewHolder from disappearing list.
     * @param holder The ViewHolder to be removed from the disappearing list.
     */
    void removeFromDisappearedInLayout(ViewHolder holder) {
        InfoRecord record = mLayoutHolderMap.get(holder);
        if (record == null) {
            return;
        }
        record.flags &= ~FLAG_DISAPPEARED;
    }

    void process(ProcessCallback callback) {
        for (int index = mLayoutHolderMap.size() - 1; index >= 0; index --) {
            final ViewHolder viewHolder = mLayoutHolderMap.keyAt(index);
            final InfoRecord record = mLayoutHolderMap.removeAt(index);
            if ((record.flags & FLAG_APPEAR_AND_DISAPPEAR) == FLAG_APPEAR_AND_DISAPPEAR) {
                // Appeared then disappeared. Not useful for animations.
                callback.unused(viewHolder);
            } else if ((record.flags & FLAG_DISAPPEARED) != 0) {
                // Set as "disappeared" by the LayoutManager (addDisappearingView)
                callback.processDisappeared(viewHolder, record.preInfo, record.postInfo);
            } else if ((record.flags & FLAG_APPEAR_PRE_AND_POST) == FLAG_APPEAR_PRE_AND_POST) {
                // Appeared in the layout but not in the adapter (e.g. entered the viewport)
                callback.processAppeared(viewHolder, record.preInfo, record.postInfo);
            } else if ((record.flags & FLAG_PRE_AND_POST) == FLAG_PRE_AND_POST) {
                // Persistent in both passes. Animate persistence
                callback.processPersistent(viewHolder, record.preInfo, record.postInfo);
            } else if ((record.flags & FLAG_PRE) != 0) {
                // Was in pre-layout, never been added to post layout
                callback.processDisappeared(viewHolder, record.preInfo, null);
            } else if ((record.flags & FLAG_POST) != 0) {
                // Was not in pre-layout, been added to post layout
                callback.processAppeared(viewHolder, record.preInfo, record.postInfo);
            } else if ((record.flags & FLAG_APPEAR) != 0) {
                // Scrap view. RecyclerView will handle removing/recycling this.
            } else if (DEBUG) {
                throw new IllegalStateException("record without any reasonable flag combination:/");
            }
            InfoRecord.recycle(record);
        }
    }

    /**
     * Removes the ViewHolder from all list
     * @param holder The ViewHolder which we should stop tracking
     */
    void removeViewHolder(ViewHolder holder) {
        for (int i = mOldChangedHolders.size() - 1; i >= 0; i--) {
            if (holder == mOldChangedHolders.valueAt(i)) {
                mOldChangedHolders.removeAt(i);
                break;
            }
        }
        final InfoRecord info = mLayoutHolderMap.remove(holder);
        if (info != null) {
            InfoRecord.recycle(info);
        }
    }

    void onDetach() {
        InfoRecord.drainCache();
    }

    interface ProcessCallback {
        void processDisappeared(ViewHolder viewHolder, ItemHolderInfo preInfo,
                @Nullable ItemHolderInfo postInfo);
        void processAppeared(ViewHolder viewHolder, @Nullable ItemHolderInfo preInfo,
                ItemHolderInfo postInfo);
        void processPersistent(ViewHolder viewHolder, @NonNull ItemHolderInfo preInfo,
                @NonNull ItemHolderInfo postInfo);
        void unused(ViewHolder holder);
    }

    static class InfoRecord {
        // disappearing list
        static final int FLAG_DISAPPEARED = 1;
        // appear in pre layout list
        static final int FLAG_APPEAR = 1 << 1;
        // pre layout, this is necessary to distinguish null item info
        static final int FLAG_PRE = 1 << 2;
        // post layout, this is necessary to distinguish null item info
        static final int FLAG_POST = 1 << 3;
        static final int FLAG_APPEAR_AND_DISAPPEAR = FLAG_APPEAR | FLAG_DISAPPEARED;
        static final int FLAG_PRE_AND_POST = FLAG_PRE | FLAG_POST;
        static final int FLAG_APPEAR_PRE_AND_POST = FLAG_APPEAR | FLAG_PRE | FLAG_POST;
        int flags;
        @Nullable ItemHolderInfo preInfo;
        @Nullable ItemHolderInfo postInfo;
        static Pools.Pool<InfoRecord> sPool = new Pools.SimplePool<>(20);

        private InfoRecord() {
        }

        static InfoRecord obtain() {
            InfoRecord record = sPool.acquire();
            return record == null ? new InfoRecord() : record;
        }

        static void recycle(InfoRecord record) {
            record.flags = 0;
            record.preInfo = null;
            record.postInfo = null;
            sPool.release(record);
        }

        static void drainCache() {
            //noinspection StatementWithEmptyBody
            while (sPool.acquire() != null);
        }
    }
}