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Android Reference

FileBackupHelper


android.app.backup

Class FileBackupHelper

  • All Implemented Interfaces:
    BackupHelper


    public class FileBackupHelper
    extends Object
    implements BackupHelper
    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(android.content.Context, java.lang.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.

    • Constructor Detail

      • FileBackupHelper

        public FileBackupHelper(Context context,
                        String... files)
        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.
    • Method Detail

      • performBackup

        public 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. When oldState is null, all the files will be backed up.

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

        Specified by:
        performBackup in interface BackupHelper
        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.
      • finalize

        protected void finalize()
                         throws Throwable
        Description copied from class: Object
        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.

        Overrides:
        finalize in class Object
        Throws:
        Throwable


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