public interface PersistenceCallback
toSave- A list of new or modified data which must be saved. The
keyis safe for filename and any other system sensitive to special characters. The
valuemust be saved.
toDelete- A list of data which must be deleted. For this method to return
true, each item in this collection must not exist by the time this method completes.
trueif the data were correctly saved and deleted, otherwise
DataStorage.restore()is called. Will be invoked on the same thread.