public void unregisterCallbacks(){
  mBrightnessObserver.stopObserving();
  mChangeCallbacks.clear();
  mUserTracker.stopTracking();
}

public void unregisterCallbacks ( ) { mBrightnessObserver . stopObserving ( ) ; mChangeCallbacks . clear ( ) ; mUserTracker . stopTracking ( ) ; }
unregister all call backs , both to and from the controller
