Added in API level 8

SharedPreferencesBackupHelper


public class SharedPreferencesBackupHelper
extends Object implements BackupHelper

java.lang.Object
   ↳ android.app.backup.SharedPreferencesBackupHelper


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 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 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 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";

     // Allocate a helper and install it.
     public 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.

Inherited methods

Public constructors

SharedPreferencesBackupHelper

Added in API level 8
public SharedPreferencesBackupHelper (Context context, 
                String... prefGroups)

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

Parameters
context Context: The application Context

prefGroups String: The names of each SharedPreferences file to back up

Public methods

performBackup

Added in API level 8
public void performBackup (ParcelFileDescriptor oldState, 
                BackupDataOutput data, 
                ParcelFileDescriptor newState)

Backs up the configured SharedPreferences groups.

Parameters
oldState ParcelFileDescriptor: 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 BackupDataOutput: 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 ParcelFileDescriptor: 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.

restoreEntity

Added in API level 8
public void restoreEntity (BackupDataInputStream data)

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

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

writeNewStateDescription

Added in API level 8
public 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. 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 ParcelFileDescriptor: A ParcelFileDescriptor to which the new state will be written.