Ok, I think I understand now.  You have, say, notepad focused and open your own application using a windows shortcut key combination.  You could try to prevent your application taking focus, and when launched, get the focused window.  There may be better ways, but you can always use pinvoke on user32.dll and call GetTopWindow.  Not sure where you would go from there to get the process information, but GetWindowThreadProcessId might work.