Howto make a gtkbutton send a "changed" signal?

["Till Harbaum" <lists harbaum org>]

Hi,

i am changing the UI of an existing app for mobile usage in a way that i replace
some gtkentry's with some gtkbuttons which the use some alternate input method.

I want to keep as much of the application as it is and one of the things the app expects
is that this particular widget emits a "changed" event whenever its contents changes.

So i'd like to enable my gtkbutton to emit a "changed" event, but i don't find any examples
on how to achieve that. How do i "attach" a new signal to an existing widget type?

Thanks,
  Till