Android APIs
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()
Invoked when the garbage collector has detected that this instance is no longer reachable.
[Expand]
Inherited Methods
From class java.lang.Object
From interface android.app.backup.BackupHelper

Public Constructors

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

Added in 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)

Added in 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)

Added in 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)

Added in 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 ()

Added in API level 8

Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.

Note that objects that override finalize are significantly more expensive than objects that don't. Finalizers may be run a long time after the object is no longer reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup. Note also that finalizers are run on a single VM-wide finalizer thread, so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary for a class that has a native peer and needs to call a native method to destroy that peer. Even then, it's better to provide an explicit close method (and implement Closeable), and insist that callers manually dispose of instances. This works well for something like files, but less well for something like a BigInteger where typical calling code would have to deal with lots of temporaries. Unfortunately, code that creates lots of temporaries is the worst kind of code from the point of view of the single finalizer thread.

If you must use finalizers, consider at least providing your own ReferenceQueue and having your own thread process that queue.

Unlike constructors, finalizers are not automatically chained. You are responsible for calling super.finalize() yourself.

Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.

Throws
Throwable