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/*
* Copyright (C) 2009 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.app.backup;
import android.app.QueuedWork;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.ParcelFileDescriptor;
import android.util.Log;
import java.io.File;
/**
* A helper class that can be used in conjunction with
* {@link android.app.backup.BackupAgentHelper} to manage the backup of
* {@link android.content.SharedPreferences}. Whenever a backup is performed, it
* will back up all named shared preferences that have changed since the last
* backup operation.
* <p>
* To use this class, the application's backup agent class should extend
* {@link android.app.backup.BackupAgentHelper}. Then, in the agent's
* {@link BackupAgent#onCreate()} method, an instance of this class should be
* allocated and installed as a backup/restore handler within the BackupAgentHelper
* framework. For example, an agent supporting backup and restore for
* an application with two groups of {@link android.content.SharedPreferences}
* data might look something like this:
* <pre>
* import android.app.backup.BackupAgentHelper;
* import android.app.backup.SharedPreferencesBackupHelper;
*
* public class MyBackupAgent extends BackupAgentHelper {
* // The names of the SharedPreferences groups that the application maintains. These
* // are the same strings that are passed to {@link Context#getSharedPreferences(String, int)}.
* static final String PREFS_DISPLAY = "displayprefs";
* static final String PREFS_SCORES = "highscores";
*
* // An arbitrary string used within the BackupAgentHelper implementation to
* // identify the SharedPreferenceBackupHelper's data.
* static final String MY_PREFS_BACKUP_KEY = "myprefs";
*
* // Simply allocate a helper and install it
* void onCreate() {
* SharedPreferencesBackupHelper helper =
* new SharedPreferencesBackupHelper(this, PREFS_DISPLAY, PREFS_SCORES);
* addHelper(MY_PREFS_BACKUP_KEY, helper);
* }
* }</pre>
* <p>
* No further implementation is needed; the {@link BackupAgentHelper} mechanism automatically
* dispatches the
* {@link BackupAgent#onBackup(android.os.ParcelFileDescriptor, BackupDataOutput, android.os.ParcelFileDescriptor) BackupAgent.onBackup()}
* and
* {@link BackupAgent#onRestore(BackupDataInput, int, android.os.ParcelFileDescriptor) BackupAgent.onRestore()}
* callbacks to the SharedPreferencesBackupHelper as appropriate.
*/
public class SharedPreferencesBackupHelper extends FileBackupHelperBase implements BackupHelper {
private static final String TAG = "SharedPreferencesBackupHelper";
private static final boolean DEBUG = false;
private Context mContext;
private String[] mPrefGroups;
/**
* Construct a helper for backing up and restoring the
* {@link android.content.SharedPreferences} under the given names.
*
* @param context The application {@link android.content.Context}
* @param prefGroups The names of each {@link android.content.SharedPreferences} file to
* back up
*/
public SharedPreferencesBackupHelper(Context context, String... prefGroups) {
super(context);
mContext = context;
mPrefGroups = prefGroups;
}
/**
* Backs up the configured {@link android.content.SharedPreferences} groups.
*/
public void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
ParcelFileDescriptor newState) {
Context context = mContext;
// If a SharedPreference has an outstanding write in flight,
// wait for it to finish flushing to disk.
QueuedWork.waitToFinish();
// make filenames for the prefGroups
String[] prefGroups = mPrefGroups;
final int N = prefGroups.length;
String[] files = new String[N];
for (int i=0; i<N; i++) {
files[i] = context.getSharedPrefsFile(prefGroups[i]).getAbsolutePath();
}
// go
performBackup_checked(oldState, data, newState, files, prefGroups);
}
/**
* Restores one entity from the restore data stream to its proper shared
* preferences file store.
*/
public void restoreEntity(BackupDataInputStream data) {
Context context = mContext;
String key = data.getKey();
if (DEBUG) Log.d(TAG, "got entity '" + key + "' size=" + data.size());
if (isKeyInList(key, mPrefGroups)) {
File f = context.getSharedPrefsFile(key).getAbsoluteFile();
writeFile(f, data);
}
}
}
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