Signal when a widget is shown on the screen.

[Alex Buoy <alex buoy eiffel com>]

Hi!

I'd like to connect a callback to a widget when it is shown on the screen.
"show" signal does not do what I want as a widget can be shown be not visible
on the screen.
Is there any signal for that? And for the contrary, when it is hidden ( I
tried to use "hide" but it did not do what I wanted either.).

Thank you very much for your help.

Alex.