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| 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:
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 | |||||||||||
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Construct a helper for backing up and restoring the
SharedPreferences under the given names.
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| Public Methods | |||||||||||
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Backs up the configured
SharedPreferences groups.
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Restores one entity from the restore data stream to its proper shared
preferences file store.
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Called by
BackupAgentHelper
after a restore operation to write the backup state file corresponding to
the data as processed by the helper.
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| Protected Methods | |||||||||||
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Invoked when the garbage collector has detected that this instance is no longer reachable.
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Inherited Methods | |||||||||||
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From class
java.lang.Object
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|
From interface
android.app.backup.BackupHelper
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Construct a helper for backing up and restoring the
SharedPreferences under the given names.
| context | The application Context |
|---|---|
| prefGroups | The names of each SharedPreferences file to
back up
|
Backs up the configured SharedPreferences groups.
| 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.
|
Restores one entity from the restore data stream to its proper shared preferences file store.
| data | An open BackupDataInputStream from which the backup data can be read.
|
|---|
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.
| fd | A ParcelFileDescriptor to which the new state will be
written.
|
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Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.
Note that objects that override finalize are significantly more expensive than
objects that don't. Finalizers may be run a long time after the object is no longer
reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup.
Note also that finalizers are run on a single VM-wide finalizer thread,
so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary
for a class that has a native peer and needs to call a native method to destroy that peer.
Even then, it's better to provide an explicit close method (and implement
Closeable), and insist that callers manually dispose of instances. This
works well for something like files, but less well for something like a BigInteger
where typical calling code would have to deal with lots of temporaries. Unfortunately,
code that creates lots of temporaries is the worst kind of code from the point of view of
the single finalizer thread.
If you must use finalizers, consider at least providing your own
ReferenceQueue and having your own thread process that queue.
Unlike constructors, finalizers are not automatically chained. You are responsible for
calling super.finalize() yourself.
Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.
| Throwable |
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