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/*
* Copyright (C) 2017 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 android.support.annotation.AnyThread;
import android.support.annotation.MainThread;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.annotation.WorkerThread;
import java.util.concurrent.Executor;
class TiledPagedList<T> extends PagedList<T>
implements PagedStorage.Callback {
private final TiledDataSource<T> mDataSource;
@SuppressWarnings("unchecked")
private final PagedStorage<Integer, T> mKeyedStorage = (PagedStorage<Integer, T>) mStorage;
private final PageResult.Receiver<Integer, T> mReceiver =
new PageResult.Receiver<Integer, T>() {
@AnyThread
@Override
public void postOnPageResult(@NonNull final PageResult<Integer, T> pageResult) {
// NOTE: if we're already on main thread, this can delay page receive by a frame
mMainThreadExecutor.execute(new Runnable() {
@Override
public void run() {
onPageResult(pageResult);
}
});
}
@MainThread
@Override
public void onPageResult(@NonNull PageResult<Integer, T> pageResult) {
if (pageResult.page == null) {
detach();
return;
}
if (isDetached()) {
// No op, have detached
return;
}
if (mStorage.getPageCount() == 0) {
mKeyedStorage.init(
pageResult.leadingNulls, pageResult.page, pageResult.trailingNulls,
pageResult.positionOffset, TiledPagedList.this);
} else {
mKeyedStorage.insertPage(pageResult.leadingNulls, pageResult.page,
TiledPagedList.this);
}
}
};
@WorkerThread
TiledPagedList(@NonNull TiledDataSource<T> dataSource,
@NonNull Executor mainThreadExecutor,
@NonNull Executor backgroundThreadExecutor,
@NonNull Config config,
int position) {
super(new PagedStorage<Integer, T>(),
mainThreadExecutor, backgroundThreadExecutor, config);
mDataSource = dataSource;
final int pageSize = mConfig.pageSize;
final int itemCount = mDataSource.countItems();
final int firstLoadSize = Math.min(itemCount,
(Math.max(mConfig.initialLoadSizeHint / pageSize, 2)) * pageSize);
final int firstLoadPosition = computeFirstLoadPosition(
position, firstLoadSize, pageSize, itemCount);
mDataSource.loadRangeInitial(firstLoadPosition, firstLoadSize, pageSize,
itemCount, mReceiver);
}
static int computeFirstLoadPosition(int position, int firstLoadSize, int pageSize, int size) {
int idealStart = position - firstLoadSize / 2;
int roundedPageStart = Math.round(idealStart / pageSize) * pageSize;
// minimum start position is 0
roundedPageStart = Math.max(0, roundedPageStart);
// maximum start pos is that which will encompass end of list
int maximumLoadPage = ((size - firstLoadSize + pageSize - 1) / pageSize) * pageSize;
roundedPageStart = Math.min(maximumLoadPage, roundedPageStart);
return roundedPageStart;
}
@Override
boolean isContiguous() {
return false;
}
@Nullable
@Override
public Object getLastKey() {
return mLastLoad;
}
@Override
protected void dispatchUpdatesSinceSnapshot(@NonNull PagedList<T> pagedListSnapshot,
@NonNull Callback callback) {
//noinspection UnnecessaryLocalVariable
final PagedStorage<?, T> snapshot = pagedListSnapshot.mStorage;
// loop through each page and signal the callback for any pages that are present now,
// but not in the snapshot.
final int pageSize = mConfig.pageSize;
final int leadingNullPages = mStorage.getLeadingNullCount() / pageSize;
final int pageCount = mStorage.getPageCount();
for (int i = 0; i < pageCount; i++) {
int pageIndex = i + leadingNullPages;
int updatedPages = 0;
// count number of consecutive pages that were added since the snapshot...
while (updatedPages < mStorage.getPageCount()
&& mStorage.hasPage(pageSize, pageIndex + updatedPages)
&& !snapshot.hasPage(pageSize, pageIndex + updatedPages)) {
updatedPages++;
}
// and signal them all at once to the callback
if (updatedPages > 0) {
callback.onChanged(pageIndex * pageSize, pageSize * updatedPages);
i += updatedPages - 1;
}
}
}
@Override
protected void loadAroundInternal(int index) {
mStorage.allocatePlaceholders(index, mConfig.prefetchDistance, mConfig.pageSize, this);
}
@Override
public void onInitialized(int count) {
notifyInserted(0, count);
}
@Override
public void onPagePrepended(int leadingNulls, int changed, int added) {
throw new IllegalStateException("Contiguous callback on TiledPagedList");
}
@Override
public void onPageAppended(int endPosition, int changed, int added) {
throw new IllegalStateException("Contiguous callback on TiledPagedList");
}
@Override
public void onPagePlaceholderInserted(final int pageIndex) {
// placeholder means initialize a load
mBackgroundThreadExecutor.execute(new Runnable() {
@Override
public void run() {
if (isDetached()) {
return;
}
final int pageSize = mConfig.pageSize;
mDataSource.loadRange(pageIndex * pageSize, pageSize, mReceiver);
}
});
}
@Override
public void onPageInserted(int start, int count) {
notifyChanged(start, count);
}
}
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