Why is CursorLoader onLoaderReset() called after device rotation?

Question

I have a main Activity A that uses a CursorLoader to query a DB. This I create in the activity onCreate() method:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ...
    getSupportLoaderManager().initLoader(LOADER_MEASUREMENTS, null, A.this);
}

Activity A also implements the 3 callbacks for the CursorLoader:

public Loader<Cursor> onCreateLoader(int loaderId, Bundle args)
public void onLoadFinished(Loader<Cursor> loader, Cursor cursor)
public void onLoaderReset(Loader<Cursor> loader)

When I rotate the device, I see the correct lifecycle methods run:

A.onPause()
A.onStop()
A.onDestroy()          
A.onCreate()      <-- re-connect to existing loader, onCreateLoader() not called
A.onLoadFinished()
A.onStart()
A.onResume()

Then I open a sub-Activity B and rotate my device. When I finish B and return to Activity A I see the following run:

B.onPause()
       A.onLoaderReset()      <- why does this run?
       A.onDestroy()          
       A.onCreate()
       A.onCreateLoader()     <- now runs as loader is null
       A.onStart()
       ...

Why is my loader reset because I had Activity B open and did a device rotate? Just to add that Activity B has nothing to do with the DB or the CursorLoader.

Answer 1

I checked the LoaderManager source code you'll find this method:

/**
     * Stops and removes the loader with the given ID.  If this loader
     * had previously reported data to the client through
     * {@link LoaderCallbacks#onLoadFinished(Loader, Object)}, a call
     * will be made to {@link LoaderCallbacks#onLoaderReset(Loader)}.
     */
    public abstract void destroyLoader(int id);

It appears that you loader gets destroyed when rotating the screen (due to configuration change). The LoaderManager internally calls the destroyLoader method which in turn calls the onLoaderReset callback method.