Signal handler not called

[Luca Cappa <luca cappa i-medlab com>]

Hello,

I created a custom widget which extends the Gtk::Frame class. I add to 
it a HBox and inside this box a gtkglextmm widget (which extends from 
Gtk::DrawingArea and public Gtk::GL::Widget<View2D>), and a Gtk::HScale. 
In the constructor of the Gtk::Frame custom class i put:

   mScale.set_digits (0);
   mScale.set_draw_value (true);
   crap = mScale.signal_value_changed ().connect (
       sigc::mem_fun (*this, &klSliceViewer::sliderChangedEvent));
   std::cout << (crap.connected () ? "connected" : "unconnected") << 
std::endl;
   std::cout << (crap.empty () ? "empty" : "not empty") << std::endl;
   Gtk::Adjustment lAdj (0, 0, 255, 1, 1, 0);
   mScale.set_adjustment  (lAdj);
   add (mBox);
   mBox.pack_start (mView2D);
   mBox.pack_start (mScale, Gtk::PACK_SHRINK, 0);

and I wonder why the klSliceViewer::sliderChangedEvent never get called. 
The printed values are "connected" and "not empty", and "crap" is a 
class member variable.

Any help?

Greetings,
Luca