BackupHelper.javaAPI DocAndroid 5.1 API5134Thu Mar 12 22:22:10 GMT


public interface BackupHelper
Defines the calling interface that {@link 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 {@link BackupAgentHelper}, with each helper given a chance to access its own saved state from within the state record produced during the previous backup operation.


Fields Summary
Constructors Summary
Methods Summary
public voidperformBackup(android.os.ParcelFileDescriptor oldState, BackupDataOutput data, android.os.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.

Implementing this method is much like implementing {@link BackupAgent#onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor) onBackup()} — the method parameters are the same. When this method is invoked the {@code oldState} descriptor points to the beginning of the state data written during this helper's previous backup operation, and the {@code 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 {@code oldState} or the {@code newState} file descriptors.

oldState An open, read-only {@link android.os.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 {@link 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 {@link android.os.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 voidrestoreEntity(BackupDataInputStream data)
Called by {@link 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 {@link size()} bytes from data.

data An open {@link BackupDataInputStream} from which the backup data can be read.

public voidwriteNewStateDescription(android.os.ParcelFileDescriptor newState)
Called by {@link 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 {@link #performBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor) performBackup()} method.

This method will be called even if the handler's {@link #restoreEntity(BackupDataInputStream) restoreEntity()} method was never invoked during the restore operation.

Note: The helper should not close or seek the {@code newState} file descriptor.

newState A {@link android.os.ParcelFileDescriptor} to which the new state will be written.