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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";

     // 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 by the garbage collector on an object when garbage collection determines that there are no more references to the object.

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.

Protected methods

finalize

added in API level 8
protected void finalize ()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

The general contract of finalize is that it is invoked if and when the Java™ virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.

The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.

Throws
Throwable