1 /*
2  * Copyright (C) 2010 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 com.example.android.backuprestore;
18 
19 import java.io.IOException;
20 
21 import android.app.backup.BackupAgentHelper;
22 import android.app.backup.BackupDataInput;
23 import android.app.backup.BackupDataOutput;
24 import android.app.backup.FileBackupHelper;
25 import android.os.ParcelFileDescriptor;
26 
27 /**
28  * This agent backs up the application's data using the BackupAgentHelper
29  * infrastructure.  In this application's case, the backup data is merely
30  * a duplicate of the stored data file; that makes it a perfect candidate
31  * for backing up using the {@link android.app.backup.FileBackupHelper} class
32  * provided by the Android operating system.
33  *
34  * <p>"Backup helpers" are a general mechanism that an agent implementation
35  * uses by extending {@link BackupAgentHelper} rather than the basic
36  * {@link BackupAgent} class.
37  *
38  * <p>By itself, the FileBackupHelper is properly handling the backup and
39  * restore of the datafile that we've configured it with, but it does
40  * not know about the potential need to use locking around its access
41  * to it.  However, it is straightforward to override
42  * {@link #onBackup()} and {@link #onRestore()} to supply the necessary locking
43  * around the helper's operation.
44  */
45 public class FileHelperExampleAgent extends BackupAgentHelper {
46     /**
47      * The "key" string passed when adding a helper is a token used to
48      * disambiguate between entities supplied by multiple different helper
49      * objects.  They only need to be unique among the helpers within this
50      * one agent class, not globally unique.
51      */
52     static final String FILE_HELPER_KEY = "the_file";
53 
54     /**
55      * The {@link android.app.backup.FileBackupHelper FileBackupHelper} class
56      * does nearly all of the work for our use case:  backup and restore of a
57      * file stored within our application's getFilesDir() location.  It will
58      * also handle files stored at any subpath within that location.  All we
59      * need to do is a bit of one-time configuration: installing the helper
60      * when this agent object is created.
61      */
62     @Override
onCreate()63     public void onCreate() {
64         // All we need to do when working within the BackupAgentHelper mechanism
65         // is to install the helper that will process and back up the files we
66         // care about.  In this case, it's just one file.
67         FileBackupHelper helper = new FileBackupHelper(this, BackupRestoreActivity.DATA_FILE_NAME);
68         addHelper(FILE_HELPER_KEY, helper);
69     }
70 
71     /**
72      * We want to ensure that the UI is not trying to rewrite the data file
73      * while we're reading it for backup, so we override this method to
74      * supply the necessary locking.
75      */
76     @Override
onBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)77     public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
78              ParcelFileDescriptor newState) throws IOException {
79         // Hold the lock while the FileBackupHelper performs the backup operation
80         synchronized (BackupRestoreActivity.sDataLock) {
81             super.onBackup(oldState, data, newState);
82         }
83     }
84 
85     /**
86      * Adding locking around the file rewrite that happens during restore is
87      * similarly straightforward.
88      */
89     @Override
onRestore(BackupDataInput data, int appVersionCode, ParcelFileDescriptor newState)90     public void onRestore(BackupDataInput data, int appVersionCode,
91             ParcelFileDescriptor newState) throws IOException {
92         // Hold the lock while the FileBackupHelper restores the file from
93         // the data provided here.
94         synchronized (BackupRestoreActivity.sDataLock) {
95             super.onRestore(data, appVersionCode, newState);
96         }
97     }
98 }
99