Loader is an abstract class that performs asynchronous loading of data.
A class that performs asynchronous loading of data. While Loaders are active they should monitor the source of their data and deliver new results when the contents change.
Note on threading: Clients of loaders should as a rule perform any calls on to a Loader from the main thread of their process (that is, the thread the Activity callbacks and other things occur on). Subclasses of Loader (such as AsyncTaskLoader) will often perform their work in a separate thread, but when delivering their results this too should be done on the main thread.
Most implementations should not derive directly from this class, but instead inherit from AsyncTaskLoader.
