Widgets not available in Glade

[Ney André de Mello Zunino <zunino inf ufsc br>]

Hello.

Since 1) my application's UI is all built with Glade; 2) I would like to 
use a Gtk::ComboBoxText element which is not available in Glade; and 3) 
get_widget_derived() requires a special constructor form, I thought that 
the way to go would be to derive from Gtk::ComboBoxText, like the 
following code snippet:

class MyComboBoxText : public Gtk::ComboBoxText
{
    public:
        MyComboBoxText(BaseObjectType* cobject,
                       const Glib::RefPtr<Gnome::Glade::Xml>& refGlade)
        : Gtk::ComboBoxText(cobject)
        {
        }
        virtual ~MyComboBoxText() {}
};

The first thing I noticed was that the elements entered in Glade would 
not show up. So I tried adding them with 
Gtk::ComboBoxText::append_text(). This time they do show up, but twice 
per line, as if in a 2 column layout. How can I make it so that my 
ComboBoxText derived class uses the default m_text_columns which is a 
protected member of the Gtk::ComboBoxText class?

As a general related question, what's the way to go in a situation like 
this, where the widget needed is not directly available in Glade but one 
wishes to have all the UI defined there as opposed to mixing libglademm 
calls and manual widget instantiation/definition?

Thank you for any insights,

--
Ney André de Mello Zunino