How to grey out menu items

[Stefan Salewski <mail ssalewski de>]

OK, gtk_widget_set_sensitive () will do it.

But I wonder how to do it for menu items that change sensitively often,
for example COPY menu item. I can set it sensitive whenever something
is selected in my application, for example a word in a text editor, and
make it insensitive if nothing is selected. Of course this generates
much noise. May it be better, and is it possible to do that on the fly,
when the pulldown menu pops on? Maybe a signal which is emitted before
the item becomes visible? Can not find something like that
unfortunately.