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/*
* Copyright (C) 2009 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.app.backup;
import android.os.ParcelFileDescriptor;
/**
* Defines the calling interface that {@link BackupAgentHelper} uses
* when dispatching backup and restore operations to the installed helpers.
* Applications can define and install their own helpers as well as using those
* provided as part of the Android framework.
*
* Although multiple helper objects may be installed simultaneously, each helper
* is responsible only for handling its own data, and will not see entities
* created by other components within the backup system. Invocations of multiple
* helpers are performed sequentially by the {@link BackupAgentHelper}, with each
* helper given a chance to access its own saved state from within the state record
* produced during the previous backup operation.
*
* @see BackupAgentHelper
* @see FileBackupHelper
* @see SharedPreferencesBackupHelper
*/
public interface BackupHelper {
/**
* Based on oldState, determine what application content
* needs to be backed up, write it to data, and fill in
* newState with the complete state as it exists now.
*
* Implementing this method is much like implementing
* {@link BackupAgent#onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor)
* onBackup()} — the method parameters are the same. When this method is invoked the
* {@code oldState} descriptor points to the beginning of the state data
* written during this helper's previous backup operation, and the {@code newState}
* descriptor points to the file location at which the helper should write its
* new state after performing the backup operation.
*
* Note: The helper should not close or seek either the {@code oldState} or
* the {@code newState} file descriptors. It is essential that when reading the helper's
* saved state from the {@code oldState} file, no extra content is consumed beyond
* what was stored by this helper. If more old state data is read, even accidentally,
* it will make it impossible for additional helpers that may be invoked after this one
* to properly reconstruct their prior state.
*
* @param oldState An open, read-only {@link android.os.ParcelFileDescriptor} pointing to the
* last backup state provided by the application. May be
* null, in which case no prior state is being
* provided and the application should perform a full backup.
* @param data An open, read/write {@link BackupDataOutput}
* pointing to the backup data destination.
* Typically the application will use backup helper classes to
* write to this file.
* @param newState An open, read/write {@link android.os.ParcelFileDescriptor} pointing to an
* empty file. The application should record the final backup
* state here after writing the requested data to the data
* output stream.
*/
public void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
ParcelFileDescriptor newState);
/**
* Called by {@link android.app.backup.BackupAgentHelper BackupAgentHelper}
* to restore a single entity from the restore data set. This method will be
* called for each entity in the data set that belongs to this handler.
*
* Note: Do not close the data stream. Do not read more than
* {@link android.app.backup.BackupDataInputStream#size() size()} bytes from
* data.
*
* @param data An open {@link BackupDataInputStream} from which the backup data can be read.
*/
public void restoreEntity(BackupDataInputStream data);
/**
* Called by {@link android.app.backup.BackupAgentHelper BackupAgentHelper}
* after a restore operation to write the backup state file corresponding to
* the data as processed by the helper. The data written here will be
* available to the helper during the next call to its
* {@link #performBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor)
* performBackup()} method.
*
* This method will be called even if the handler's
* {@link #restoreEntity(BackupDataInputStream) restoreEntity()} method was never invoked during
* the restore operation.
*
* Note: The helper should not close or seek the {@code newState}
* file descriptor.
*
* @param newState A {@link android.os.ParcelFileDescriptor} to which the new state will be
* written.
*/
public void writeNewStateDescription(ParcelFileDescriptor newState);
}