Interface INeedFocus

An interface of component classes requiring the user's focus. For example, the ContextMenu which that it requires the user to focus on itself all the time it is being displayed. Once the user click on anywhere else outside its area (losing its focus), the ContextMenu will be disappeared. For this kind of requirement, the ContextMenu must implement this interface and register itself as a focusing component to NeedFocusService (via NeedFocusService.setFocusingComponent method). Then, NeedFocusService will automatically call onFocus callback method on the focusing component. Once the component loses its focus, NeedFocusService will automatically call onLostFocus callback method.