> So, when the menu bar gets clicked, a signal gets emitted in the Menu
> Bar object.  How can the Application Window object know that a menu
> bar gets clicked?  Do I need to create a new signal to notify the
> Application Window?

Just define a handler for the signal that calls methods on the
application window object, either finding it based on navigating up the
widget tree, or just hard-coding:

class MenuBar < Gtk::MenuBar
  def initialize(app)
    super()
    # create menu buttons
    @app = app
    # here, connect_signal -- connect_signal('clicked') { @app.frob }
    show
  end
end

And pass the app to the menu bar at init time.

Ari