wy signal handler could not be override

["Klaus Rudolph" <lts-rudolph gmx de>]

I want to override a signal handler in a derived class:
 
class MyRect : public Goocanvas::Rect
{
    public:
        MyRect( double x, double y, double w, double h):
            Goocanvas::Rect( x,y,w,h)
    {
    }

    public:
        bool on_button_press_event(const Glib::RefPtr<Item>& target, GdkEventButton* event)
        {
            cout << "catch it" << endl;
            return true;
        }
};

But the handler is never invoked!

Any advice how to override a signal handler?

Manual adding the handler by

(Glib::RefPtr<Goocanvas::Item>&)m_rect_own)->signal_button_press_event().connect(sigc::ptr_fun(&MyHandler4));

works. But this is not very handy :-(

Regards
 Klaus