title: Create a new Event Handler and Source
body: <p>I have a User Interface(UI) class. It creates some thread (lets call it T) to do some work. I want my UI class to be notified when T is done working.
  I think I need to create an event handler in UI class (among onClick() etc) and trigger it from T.
  Question: Is this possible ? How ?
  //to be clear, UI class does already have some event Handlers which are triggered by functions I didn't write. like onClick() , etc.</p>