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
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:
Developers
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 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.
Public constructors | |
|---|---|
SharedPreferencesBackupHelper(Context context, String... prefGroups)
Construct a helper for backing up and restoring the
|
|
Public methods | |
|---|---|
void
|
performBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)
Backs up the configured |
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 |
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 | |
|---|---|
 From
class
java.lang.Object
| |
From
interface
android.app.backup.BackupHelper
| |
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
|
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.
|
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.
|
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.
|
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 JavaTM 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 |
|