public abstract uint add_focus_handler (FocusHandler handler)
Warning: add_focus_handler is deprecated since 2.9.4.
Add the specified handler to the set of functions to be called when this object receives focus events (in or out).
If you need to track when an object gains or lose the focus, use the state_change "focused" notification instead.
If the handler is already added it is not added again
The Component to attach the
The FocusHandler to be attached to this
a handler id which can be used in remove_focus_handler or zero if the handler was already added.