Android APIs
Added in API level 8
public interface

BackupHelper

android.app.backup.BackupHelper
Known Indirect Subclasses

Class Overview

Defines the calling interface that BackupAgentHelper uses when dispatching backup and restore operations to the installed helpers. Applications can define and install their own helpers as well as using those provided as part of the Android framework.

Although multiple helper objects may be installed simultaneously, each helper is responsible only for handling its own data, and will not see entities created by other components within the backup system. Invocations of multiple helpers are performed sequentially by the BackupAgentHelper, with each helper given a chance to access its own saved state from within the state record produced during the previous backup operation.

Summary

Public Methods
abstract void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)
Based on oldState, determine what application content needs to be backed up, write it to data, and fill in newState with the complete state as it exists now.
abstract void restoreEntity(BackupDataInputStream data)
Called by BackupAgentHelper to restore a single entity from the restore data set.
abstract void writeNewStateDescription(ParcelFileDescriptor newState)
Called by BackupAgentHelper after a restore operation to write the backup state file corresponding to the data as processed by the helper.

Public Methods

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

Added in API level 8

Based on oldState, determine what application content needs to be backed up, write it to data, and fill in newState with the complete state as it exists now.

Implementing this method is much like implementing onBackup() — the method parameters are the same. When this method is invoked the oldState descriptor points to the beginning of the state data written during this helper's previous backup operation, and the newState descriptor points to the file location at which the helper should write its new state after performing the backup operation.

Note: The helper should not close or seek either the oldState or the newState file descriptors.

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.

public abstract void restoreEntity (BackupDataInputStream data)

Added in API level 8

Called by BackupAgentHelper to restore a single entity from the restore data set. This method will be called for each entity in the data set that belongs to this handler.

Note: Do not close the data stream. Do not read more than size() bytes from data.

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

public abstract void writeNewStateDescription (ParcelFileDescriptor newState)

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
newState ParcelFileDescriptor: A ParcelFileDescriptor to which the new state will be written.