109 lines
5.4 KiB
Java
109 lines
5.4 KiB
Java
/*
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* Copyright (C) 2009 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.app.backup;
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import android.os.ParcelFileDescriptor;
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/**
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* Defines the calling interface that {@link BackupAgentHelper} uses
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* when dispatching backup and restore operations to the installed helpers.
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* Applications can define and install their own helpers as well as using those
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* provided as part of the Android framework.
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* <p>
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* Although multiple helper objects may be installed simultaneously, each helper
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* is responsible only for handling its own data, and will not see entities
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* created by other components within the backup system. Invocations of multiple
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* helpers are performed sequentially by the {@link BackupAgentHelper}, with each
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* helper given a chance to access its own saved state from within the state record
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* produced during the previous backup operation.
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*
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* @see BackupAgentHelper
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* @see FileBackupHelper
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* @see SharedPreferencesBackupHelper
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*/
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public interface BackupHelper {
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/**
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* Based on <code>oldState</code>, determine what application content
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* needs to be backed up, write it to <code>data</code>, and fill in
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* <code>newState</code> with the complete state as it exists now.
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* <p>
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* Implementing this method is much like implementing
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* {@link BackupAgent#onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor)
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* onBackup()} — the method parameters are the same. When this method is invoked the
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* {@code oldState} descriptor points to the beginning of the state data
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* written during this helper's previous backup operation, and the {@code newState}
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* descriptor points to the file location at which the helper should write its
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* new state after performing the backup operation.
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* <p class="note">
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* <strong>Note:</strong> The helper should not close or seek either the {@code oldState} or
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* the {@code newState} file descriptors. It is essential that when reading the helper's
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* saved state from the {@code oldState} file, no extra content is consumed beyond
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* what was stored by this helper. If more old state data is read, even accidentally,
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* it will make it impossible for additional helpers that may be invoked after this one
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* to properly reconstruct their prior state.</p>
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*
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* @param oldState An open, read-only {@link android.os.ParcelFileDescriptor} pointing to the
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* last backup state provided by the application. May be
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* <code>null</code>, in which case no prior state is being
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* provided and the application should perform a full backup.
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* @param data An open, read/write {@link BackupDataOutput}
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* pointing to the backup data destination.
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* Typically the application will use backup helper classes to
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* write to this file.
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* @param newState An open, read/write {@link android.os.ParcelFileDescriptor} pointing to an
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* empty file. The application should record the final backup
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* state here after writing the requested data to the <code>data</code>
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* output stream.
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*/
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public void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
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ParcelFileDescriptor newState);
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/**
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* Called by {@link android.app.backup.BackupAgentHelper BackupAgentHelper}
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* to restore a single entity from the restore data set. This method will be
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* called for each entity in the data set that belongs to this handler.
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* <p class="note">
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* <strong>Note:</strong> Do not close the <code>data</code> stream. Do not read more than
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* {@link android.app.backup.BackupDataInputStream#size() size()} bytes from
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* <code>data</code>.</p>
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*
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* @param data An open {@link BackupDataInputStream} from which the backup data can be read.
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*/
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public void restoreEntity(BackupDataInputStream data);
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/**
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* Called by {@link android.app.backup.BackupAgentHelper BackupAgentHelper}
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* after a restore operation to write the backup state file corresponding to
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* the data as processed by the helper. The data written here will be
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* available to the helper during the next call to its
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* {@link #performBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor)
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* performBackup()} method.
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* <p>
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* This method will be called even if the handler's
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* {@link #restoreEntity(BackupDataInputStream) restoreEntity()} method was never invoked during
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* the restore operation.
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* <p class="note">
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* <strong>Note:</strong> The helper should not close or seek the {@code newState}
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* file descriptor.</p>
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*
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* @param newState A {@link android.os.ParcelFileDescriptor} to which the new state will be
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* written.
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*/
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public void writeNewStateDescription(ParcelFileDescriptor newState);
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}
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