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• WrapperItemKeyedDataSource.java

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android.arch.paging.WrapperItemKeyedDataSource Maven / Gradle / Ivy

/*
 * Copyright 2016-2019 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.arch.paging;

import androidx.annotation.NonNull;
import androidx.arch.core.util.Function;

import java.util.IdentityHashMap;
import java.util.List;

class WrapperItemKeyedDataSource extends ItemKeyedDataSource {
    private final ItemKeyedDataSource mSource;
    private final Function, List> mListFunction;

    private final IdentityHashMap mKeyMap = new IdentityHashMap<>();

    WrapperItemKeyedDataSource(ItemKeyedDataSource source,
            Function, List> listFunction) {
        mSource = source;
        mListFunction = listFunction;
    }

    @Override
    public void addInvalidatedCallback(@NonNull InvalidatedCallback onInvalidatedCallback) {
        mSource.addInvalidatedCallback(onInvalidatedCallback);
    }

    @Override
    public void removeInvalidatedCallback(@NonNull InvalidatedCallback onInvalidatedCallback) {
        mSource.removeInvalidatedCallback(onInvalidatedCallback);
    }

    @Override
    public void invalidate() {
        mSource.invalidate();
    }

    @Override
    public boolean isInvalid() {
        return mSource.isInvalid();
    }

    private List convertWithStashedKeys(List source) {
        List dest = convert(mListFunction, source);
        synchronized (mKeyMap) {
            // synchronize on mKeyMap, since multiple loads may occur simultaneously.
            // Note: manually sync avoids locking per-item (e.g. Collections.synchronizedMap)
            for (int i = 0; i < dest.size(); i++) {
                mKeyMap.put(dest.get(i), mSource.getKey(source.get(i)));
            }
        }
        return dest;
    }

    @Override
    public void loadInitial(@NonNull LoadInitialParams params,
            final @NonNull LoadInitialCallback callback) {
        mSource.loadInitial(params, new LoadInitialCallback() {
            @Override
            public void onResult(@NonNull List data, int position, int totalCount) {
                callback.onResult(convertWithStashedKeys(data), position, totalCount);
            }

            @Override
            public void onResult(@NonNull List data) {
                callback.onResult(convertWithStashedKeys(data));
            }
        });
    }

    @Override
    public void loadAfter(@NonNull LoadParams params,
            final @NonNull LoadCallback callback) {
        mSource.loadAfter(params, new LoadCallback() {
            @Override
            public void onResult(@NonNull List data) {
                callback.onResult(convertWithStashedKeys(data));
            }
        });
    }

    @Override
    public void loadBefore(@NonNull LoadParams params,
            final @NonNull LoadCallback callback) {
        mSource.loadBefore(params, new LoadCallback() {
            @Override
            public void onResult(@NonNull List data) {
                callback.onResult(convertWithStashedKeys(data));
            }
        });
    }

    @NonNull
    @Override
    public K getKey(@NonNull B item) {
        synchronized (mKeyMap) {
            return mKeyMap.get(item);
        }
    }
}