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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.NonNull;
import android.support.annotation.Nullable;
import android.support.annotation.RestrictTo;
import android.support.annotation.WorkerThread;
import java.util.List;
/** @hide */
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
public abstract class ContiguousDataSource<Key, Value> extends DataSource<Key, Value> {
/**
* Number of items that this DataSource can provide in total, or COUNT_UNDEFINED.
*
* @return number of items that this DataSource can provide in total, or COUNT_UNDEFINED
* if difficult or undesired to compute.
*/
public int countItems() {
return COUNT_UNDEFINED;
}
@Override
boolean isContiguous() {
return true;
}
/** @hide */
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
@WorkerThread
@Nullable
public abstract NullPaddedList<Value> loadInitial(
Key key, int initialLoadSize, boolean enablePlaceholders);
/**
* Load data after the given position / item.
* <p>
* It's valid to return a different list size than the page size, if it's easier for this data
* source. It is generally safer to increase number loaded than reduce.
*
* @param currentEndIndex Load items after this index, starting with currentEndIndex + 1.
* @param currentEndItem Load items after this item, can be used for precise querying based on
* item contents.
* @param pageSize Suggested number of items to load.
* @return List of items, starting at position currentEndIndex + 1. Null if the data source is
* no longer valid, and should not be queried again.
*
* @hide
*/
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
@WorkerThread
@Nullable
public final List<Value> loadAfter(int currentEndIndex,
@NonNull Value currentEndItem, int pageSize) {
if (isInvalid()) {
return null;
}
List<Value> list = loadAfterImpl(currentEndIndex, currentEndItem, pageSize);
if (isInvalid()) {
return null;
}
return list;
}
@Nullable
abstract List<Value> loadAfterImpl(int currentEndIndex,
@NonNull Value currentEndItem, int pageSize);
/**
* Load data before the given position / item.
* <p>
* It's valid to return a different list size than the page size, if it's easier for this data
* source. It is generally safer to increase number loaded than reduce.
*
* @param currentBeginIndex Load items before this index, starting with currentBeginIndex - 1.
* @param currentBeginItem Load items after this item, can be used for precise querying based
* on item contents.
* @param pageSize Suggested number of items to load.
* @return List of items, in descending order, starting at position currentBeginIndex - 1.
*
* @hide
*/
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
@WorkerThread
@Nullable
public final List<Value> loadBefore(int currentBeginIndex,
@NonNull Value currentBeginItem, int pageSize) {
if (isInvalid()) {
return null;
}
List<Value> list = loadBeforeImpl(currentBeginIndex, currentBeginItem, pageSize);
if (isInvalid()) {
return null;
}
return list;
}
@Nullable
abstract List<Value> loadBeforeImpl(int currentBeginIndex,
@NonNull Value currentBeginItem, int pageSize);
/**
* Get the key from either the position, or item. Position may not match passed item's position,
* if trying to query the key from a position that isn't yet loaded, so a fallback item must be
* used.
*/
abstract Key getKey(int position, Value item);
}
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