1 /* 2 * Copyright (C) 2009 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package android.app.backup; 18 19 import android.os.ParcelFileDescriptor; 20 21 /** 22 * Defines the calling interface that {@link BackupAgentHelper} uses 23 * when dispatching backup and restore operations to the installed helpers. 24 * Applications can define and install their own helpers as well as using those 25 * provided as part of the Android framework. 26 * <p> 27 * Although multiple helper objects may be installed simultaneously, each helper 28 * is responsible only for handling its own data, and will not see entities 29 * created by other components within the backup system. Invocations of multiple 30 * helpers are performed sequentially by the {@link BackupAgentHelper}, with each 31 * helper given a chance to access its own saved state from within the state record 32 * produced during the previous backup operation. 33 * 34 * @see BackupAgentHelper 35 * @see FileBackupHelper 36 * @see SharedPreferencesBackupHelper 37 */ 38 public interface BackupHelper { 39 /** 40 * Based on <code>oldState</code>, determine what application content 41 * needs to be backed up, write it to <code>data</code>, and fill in 42 * <code>newState</code> with the complete state as it exists now. 43 * <p> 44 * Implementing this method is much like implementing 45 * {@link BackupAgent#onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor) 46 * onBackup()} — the method parameters are the same. When this method is invoked the 47 * {@code oldState} descriptor points to the beginning of the state data 48 * written during this helper's previous backup operation, and the {@code newState} 49 * descriptor points to the file location at which the helper should write its 50 * new state after performing the backup operation. 51 * <p class="note"> 52 * <strong>Note:</strong> The helper should not close or seek either the {@code oldState} or 53 * the {@code newState} file descriptors. It is essential that when reading the helper's 54 * saved state from the {@code oldState} file, no extra content is consumed beyond 55 * what was stored by this helper. If more old state data is read, even accidentally, 56 * it will make it impossible for additional helpers that may be invoked after this one 57 * to properly reconstruct their prior state.</p> 58 * 59 * @param oldState An open, read-only {@link android.os.ParcelFileDescriptor} pointing to the 60 * last backup state provided by the application. May be 61 * <code>null</code>, in which case no prior state is being 62 * provided and the application should perform a full backup. 63 * @param data An open, read/write {@link BackupDataOutput} 64 * pointing to the backup data destination. 65 * Typically the application will use backup helper classes to 66 * write to this file. 67 * @param newState An open, read/write {@link android.os.ParcelFileDescriptor} pointing to an 68 * empty file. The application should record the final backup 69 * state here after writing the requested data to the <code>data</code> 70 * output stream. 71 */ 72 public void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data, 73 ParcelFileDescriptor newState); 74 75 /** 76 * Called by {@link android.app.backup.BackupAgentHelper BackupAgentHelper} 77 * to restore a single entity from the restore data set. This method will be 78 * called for each entity in the data set that belongs to this handler. 79 * <p class="note"> 80 * <strong>Note:</strong> Do not close the <code>data</code> stream. Do not read more than 81 * {@link android.app.backup.BackupDataInputStream#size() size()} bytes from 82 * <code>data</code>.</p> 83 * 84 * @param data An open {@link BackupDataInputStream} from which the backup data can be read. 85 */ 86 public void restoreEntity(BackupDataInputStream data); 87 88 /** 89 * Called by {@link android.app.backup.BackupAgentHelper BackupAgentHelper} 90 * after a restore operation to write the backup state file corresponding to 91 * the data as processed by the helper. The data written here will be 92 * available to the helper during the next call to its 93 * {@link #performBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor) 94 * performBackup()} method. 95 * <p> 96 * This method will be called even if the handler's 97 * {@link #restoreEntity(BackupDataInputStream) restoreEntity()} method was never invoked during 98 * the restore operation. 99 * <p class="note"> 100 * <strong>Note:</strong> The helper should not close or seek the {@code newState} 101 * file descriptor.</p> 102 * 103 * @param newState A {@link android.os.ParcelFileDescriptor} to which the new state will be 104 * written. 105 */ 106 public void writeNewStateDescription(ParcelFileDescriptor newState); 107 } 108 109
