public class

SharedPreferencesBackupHelper

extends Object
implements BackupHelper
java.lang.Object
   ↳ android.app.backup.SharedPreferencesBackupHelper

Class Overview

A helper class that can be used in conjunction with BackupAgentHelper to manage the backup of SharedPreferences. Whenever a backup is performed, it will back up all named shared preferences that have changed since the last backup operation.

To use this class, the application's backup agent class should extend BackupAgentHelper. Then, in the agent's 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 SharedPreferences data might look something like this: 

 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 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);
     }
 }

No further implementation is needed; the BackupAgentHelper mechanism automatically dispatches the BackupAgent.onBackup() and BackupAgent.onRestore() callbacks to the SharedPreferencesBackupHelper as appropriate.

Summary

Public Constructors
SharedPreferencesBackupHelper(Context context, String... prefGroups)
Construct a helper for backing up and restoring the SharedPreferences under the given names.
Public Methods
void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)
Backs up the configured SharedPreferences groups.
void restoreEntity(BackupDataInputStream data)
Restores one entity from the restore data stream to its proper shared preferences file store.
void writeNewStateDescription(ParcelFileDescriptor fd)
Called by BackupAgentHelper after a restore operation to write the backup state file corresponding to the data as processed by the helper.
Protected Methods
void finalize()
Called before the object's memory is reclaimed by the VM.
[Expand]
Inherited Methods
From class java.lang.Object
From interface android.app.backup.BackupHelper

Public Constructors

public SharedPreferencesBackupHelper (Context context, String... prefGroups)

Since: API Level 8

Construct a helper for backing up and restoring the SharedPreferences under the given names.

Parameters
context The application Context
prefGroups The names of each SharedPreferences file to back up

Public Methods

public void performBackup (ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)

Since: API Level 8

Backs up the configured SharedPreferences groups.

Parameters
oldState An open, read-only ParcelFileDescriptor pointing to the last backup state provided by the application. May be null, in which case no prior state is being provided and the application should perform a full backup.
data An open, read/write BackupDataOutput pointing to the backup data destination. Typically the application will use backup helper classes to write to this file.
newState An open, read/write ParcelFileDescriptor pointing to an empty file. The application should record the final backup state here after writing the requested data to the data output stream.

public void restoreEntity (BackupDataInputStream data)

Since: API Level 8

Restores one entity from the restore data stream to its proper shared preferences file store.

Parameters
data An open BackupDataInputStream from which the backup data can be read.

public void writeNewStateDescription (ParcelFileDescriptor fd)

Since: API Level 8

Called by BackupAgentHelper after a restore operation to write the backup state file corresponding to the data as processed by the helper. The data written here will be available to the helper during the next call to its performBackup() method.

This method will be called even if the handler's restoreEntity() method was never invoked during the restore operation.

Note: The helper should not close or seek the newState file descriptor.

Parameters
fd A ParcelFileDescriptor to which the new state will be written.

Protected Methods

protected void finalize ()

Since: API Level 8

Called before the object's memory is reclaimed by the VM. This can only happen once the garbage collector has detected that the object is no longer reachable by any thread of the running application.

The method can be used to free system resources or perform other cleanup before the object is garbage collected. The default implementation of the method is empty, which is also expected by the VM, but subclasses can override finalize() as required. Uncaught exceptions which are thrown during the execution of this method cause it to terminate immediately but are otherwise ignored.

Note that the VM does guarantee that finalize() is called at most once for any object, but it doesn't guarantee when (if at all) finalize() will be called. For example, object B's finalize() can delay the execution of object A's finalize() method and therefore it can delay the reclamation of A's memory. To be safe, use a ReferenceQueue, because it provides more control over the way the VM deals with references during garbage collection.

Throws
Throwable