When an application has made changes to data which should be backed up, a call to dataChanged() will notify the backup service. The system will then schedule a backup operation to occur in the near future. Repeated calls to dataChanged() have no further effect until the backup operation actually occurs.
A backup or restore operation for your application begins when the system launches the BackupAgent subclass you've declared in your manifest. See the documentation for BackupAgent for a detailed description of how the operation then proceeds.
Several attributes affecting the operation of the backup and restore mechanism can be set on the tag in your application's AndroidManifest.xml file.
