public class

FileBackupHelper

extends Object
implements BackupHelper
java.lang.Object
   ↳ android.app.backup.FileBackupHelper

Class Overview

A helper class that can be used in conjunction with BackupAgentHelper to manage the backup of a set of files. Whenever backup is performed, all files changed since the last backup will be saved in their entirety. When backup first occurs, every file in the list provided to FileBackupHelper(Context, String...) will be backed up.

During restore, if the helper encounters data for a file that was not specified when the FileBackupHelper object was constructed, that data will be ignored.

Note: This should be used only with small configuration files, not large binary files.

Summary

Public Constructors
FileBackupHelper(Context context, String... files)
Construct a helper to manage backup/restore of entire files within the application's data directory hierarchy.
Public Methods
void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)
Based on oldState, determine which of the files from the application's data directory need to be backed up, write them to the data stream, and fill in newState with the state as it exists now.
void restoreEntity(BackupDataInputStream data)
Restore one record [representing a single file] from the restore dataset.
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 before the object's memory is reclaimed by the VM.
[Expand]
Inherited Methods
From class java.lang.Object
From interface android.app.backup.BackupHelper

Public Constructors

public FileBackupHelper (Context context, String... files)

Since: API Level 8

Construct a helper to manage backup/restore of entire files within the application's data directory hierarchy.

Parameters
context The backup agent's Context object
files A list of the files to be backed up or restored.

Public Methods

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

Since: API Level 8

Based on oldState, determine which of the files from the application's data directory need to be backed up, write them to the data stream, and fill in newState with the state as it exists now. When oldState is null, all the files will be backed up.

This should only be called directly from within the BackupAgentHelper implementation. See onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor) for a description of parameter meanings.

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)

Since: API Level 8

Restore one record [representing a single file] from the restore dataset.

This should only be called directly from within the BackupAgentHelper implementation.

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

public void writeNewStateDescription (ParcelFileDescriptor fd)

Since: 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 ()

Since: API Level 8

Called before the object's memory is reclaimed by the VM. This can only happen once the garbage collector has detected that the object is no longer reachable by any thread of the running application.

The method can be used to free system resources or perform other cleanup before the object is garbage collected. The default implementation of the method is empty, which is also expected by the VM, but subclasses can override finalize() as required. Uncaught exceptions which are thrown during the execution of this method cause it to terminate immediately but are otherwise ignored.

Note that the VM does guarantee that finalize() is called at most once for any object, but it doesn't guarantee when (if at all) finalize() will be called. For example, object B's finalize() can delay the execution of object A's finalize() method and therefore it can delay the reclamation of A's memory. To be safe, use a ReferenceQueue, because it provides more control over the way the VM deals with references during garbage collection.

Throws
Throwable