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| java.lang.Object | |
| ↳ | android.app.backup.FileBackupHelper |
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.
| Public Constructors | |||||||||||
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Construct a helper to manage backup/restore of entire files within the
application's data directory hierarchy.
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| Public Methods | |||||||||||
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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. | |||||||||||
Restore one record [representing a single file] from the restore dataset.
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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. | |||||||||||
| 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 to manage backup/restore of entire files within the application's data directory hierarchy.
| context | The backup agent's Context object |
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| files | A list of the files to be backed up or restored. |
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.
| 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. |
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| 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.
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Restore one record [representing a single file] from the restore dataset.
This should only be called directly from within the BackupAgentHelper
implementation.
| data | An open BackupDataInputStream from which the backup data can be read.
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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. 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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