Disable a submenu via Gio::Action

[Yann Leydier <yann leydier info>]

Hi,

in Gtkmm2 it was possible to create an action with no callback for 
submenus. It allowed me do disable submenus.

In Gtkmm3, I wrote this:
                "<interface>"
                "    <menu id='MenuBar'>"
                "        <submenu>"
                "            <attribute name='label' 
translatable='yes'>_File</attribute>"
                "            <attribute 
name='action'>app.file-menu</attribute>"
                "            <section>"
                "                <item>"
                etc.

but when I disable the "file-menu" Gio::SimpleAction (and I do it after 
the window is realized!), the submenu is not disabled. Did I do 
something wrong or is it a regression in Gtk3? How can I do it?

Thanks a lot,
yann



PS: BTW, is it possible to add to the doc that 
Gtk::Widget::insert_action_group() has no effect if the widget is not 
realized?