Use signals to communicate between GUI objects?

Say when a user selects a radio box in one part of the GUI, a couple
other parts of the GUI should change.

Should I use a gtk (glib, I think) signal for this? Or function calls
between the different objects?

I’m trying to set this up for easy unit testing, by the way. I could
use the Observer pattern, but when one part of the GUI needs to react
to a few different ‘events’, I think using one update() function
becomes difficult.

Hope that made sense…

Joe