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      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
     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
     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
     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