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      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.app.QueuedWork;
     20 import android.content.Context;
     21 import android.os.ParcelFileDescriptor;
     22 import android.util.Log;
     23 
     24 import java.io.File;
     25 
     26 /**
     27  * A helper class that can be used in conjunction with
     28  * {@link android.app.backup.BackupAgentHelper} to manage the backup of
     29  * {@link android.content.SharedPreferences}. Whenever a backup is performed, it
     30  * will back up all named shared preferences that have changed since the last
     31  * backup operation.
     32  * <p>
     33  * To use this class, the application's backup agent class should extend
     34  * {@link android.app.backup.BackupAgentHelper}.  Then, in the agent's
     35  * {@link BackupAgent#onCreate()} method, an instance of this class should be
     36  * allocated and installed as a backup/restore handler within the BackupAgentHelper
     37  * framework.  For example, an agent supporting backup and restore for
     38  * an application with two groups of {@link android.content.SharedPreferences}
     39  * data might look something like this:
     40  * <pre>
     41  * import android.app.backup.BackupAgentHelper;
     42  * import android.app.backup.SharedPreferencesBackupHelper;
     43  *
     44  * public class MyBackupAgent extends BackupAgentHelper {
     45  *     // The names of the SharedPreferences groups that the application maintains.  These
     46  *     // are the same strings that are passed to {@link Context#getSharedPreferences(String, int)}.
     47  *     static final String PREFS_DISPLAY = "displayprefs";
     48  *     static final String PREFS_SCORES = "highscores";
     49  *
     50  *     // An arbitrary string used within the BackupAgentHelper implementation to
     51  *     // identify the SharedPreferenceBackupHelper's data.
     52  *     static final String MY_PREFS_BACKUP_KEY = "myprefs";
     53  *
     54  *     // Simply allocate a helper and install it
     55  *     void onCreate() {
     56  *         SharedPreferencesBackupHelper helper =
     57  *                 new SharedPreferencesBackupHelper(this, PREFS_DISPLAY, PREFS_SCORES);
     58  *         addHelper(MY_PREFS_BACKUP_KEY, helper);
     59  *     }
     60  * }</pre>
     61  * <p>
     62  * No further implementation is needed; the {@link BackupAgentHelper} mechanism automatically
     63  * dispatches the
     64  * {@link BackupAgent#onBackup(android.os.ParcelFileDescriptor, BackupDataOutput, android.os.ParcelFileDescriptor) BackupAgent.onBackup()}
     65  * and
     66  * {@link BackupAgent#onRestore(BackupDataInput, int, android.os.ParcelFileDescriptor) BackupAgent.onRestore()}
     67  * callbacks to the SharedPreferencesBackupHelper as appropriate.
     68  */
     69 public class SharedPreferencesBackupHelper extends FileBackupHelperBase implements BackupHelper {
     70     private static final String TAG = "SharedPreferencesBackupHelper";
     71     private static final boolean DEBUG = false;
     72 
     73     private Context mContext;
     74     private String[] mPrefGroups;
     75 
     76     /**
     77      * Construct a helper for backing up and restoring the
     78      * {@link android.content.SharedPreferences} under the given names.
     79      *
     80      * @param context The application {@link android.content.Context}
     81      * @param prefGroups The names of each {@link android.content.SharedPreferences} file to
     82      * back up
     83      */
     84     public SharedPreferencesBackupHelper(Context context, String... prefGroups) {
     85         super(context);
     86 
     87         mContext = context;
     88         mPrefGroups = prefGroups;
     89     }
     90 
     91     /**
     92      * Backs up the configured {@link android.content.SharedPreferences} groups.
     93      */
     94     public void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
     95             ParcelFileDescriptor newState) {
     96         Context context = mContext;
     97 
     98         // If a SharedPreference has an outstanding write in flight,
     99         // wait for it to finish flushing to disk.
    100         QueuedWork.waitToFinish();
    101 
    102         // make filenames for the prefGroups
    103         String[] prefGroups = mPrefGroups;
    104         final int N = prefGroups.length;
    105         String[] files = new String[N];
    106         for (int i=0; i<N; i++) {
    107             files[i] = context.getSharedPrefsFile(prefGroups[i]).getAbsolutePath();
    108         }
    109 
    110         // go
    111         performBackup_checked(oldState, data, newState, files, prefGroups);
    112     }
    113 
    114     /**
    115      * Restores one entity from the restore data stream to its proper shared
    116      * preferences file store.
    117      */
    118     public void restoreEntity(BackupDataInputStream data) {
    119         Context context = mContext;
    120 
    121         String key = data.getKey();
    122         if (DEBUG) Log.d(TAG, "got entity '" + key + "' size=" + data.size());
    123 
    124         if (isKeyInList(key, mPrefGroups)) {
    125             File f = context.getSharedPrefsFile(key).getAbsoluteFile();
    126             writeFile(f, data);
    127         }
    128     }
    129 }
    130