Gtkmm + Glade = invisible DrawingArea

[Alessandro Candini <candini meeo it>]

I'm trying to get work this gtkmm doc example:
http://developer.gnome.org/gtkmm-tutorial/2.24/gtkmm-tutorial.html#cairo-example-lines

Taken as is, it works without problems...but if I try to modify it
adding a little interface created with glade (A Gtk Window with inside a
DrawingArea element), it compiles but I obtain a window with an empty
drawing area.

Here the code:
#include<gtkmm.h>
#include<iostream>
#include<fstream>
#include<iomanip>
#include<string>
#include<cairomm/context.h>

#include<gtkmm/main.h>
#include<gtkmm/window.h>
#include<gtkmm/drawingarea.h>

class MyArea : public Gtk::DrawingArea
{
     public:
         MyArea(BaseObjectType* cobject, const
Glib::RefPtr<Gtk::Builder>&  refGlade) {};
         virtual ~MyArea() {};

     protected:
         //Override default signal handler:
         virtual bool on_expose_event(GdkEventExpose* event)
         {
             // This is where we draw on the window
             Glib::RefPtr<Gdk::Window>  window = get_window();
             if(window)
             {
                 Gtk::Allocation allocation = get_allocation();
                 const int width = allocation.get_width();
                 const int height = allocation.get_height();

                 // coordinates for the center of the window
                 int xc, yc;
                 xc = width / 2;
                 yc = height / 2;

                 Cairo::RefPtr<Cairo::Context>  cr =
window->create_cairo_context();
                 cr->set_line_width(10.0);

                 // clip to the area indicated by the expose event so
that we only redraw
                 // the portion of the window that needs to be redrawn
                 cr->rectangle(event->area.x, event->area.y,
                         event->area.width, event->area.height);
                 cr->clip();

                 // draw red lines out from the center of the window
                 cr->set_source_rgb(0.8, 0.0, 0.0);
                 cr->move_to(0, 0);
                 cr->line_to(xc, yc);
                 cr->line_to(0, height);
                 cr->move_to(xc, yc);
                 cr->line_to(width, yc);
                 cr->stroke();
             }

             return true;
         }
};

int main(int argc, char** argv)
{
     Gtk::Window    *win = 0;

     Gtk::Main kit(argc, argv);

     //Load the GtkBuilder file and instantiate its widgets:
     Glib::RefPtr<Gtk::Builder>  refBuilder = Gtk::Builder::create();
     try
     {
         refBuilder->add_from_file("drawingArea.ui");
     }
     catch(const Glib::FileError&  ex)
     {
         std::cerr<<  "FileError: "<<  ex.what()<<  std::endl;
         return 1;
     }
     catch(const Gtk::BuilderError&  ex)
     {
         std::cerr<<  "BuilderError: "<<  ex.what()<<  std::endl;
         return 1;
     }

     //Get the GtkBuilder-instantiated Dialog:
     refBuilder->get_widget("window1", win);
     if(win)
     {
         MyArea *circuitDrawingArea;
         win->set_title("MTA Automotive");

         refBuilder->get_widget_derived("drawingarea1", circuitDrawingArea);
//        win->add(circuitDrawingArea);
         circuitDrawingArea->show();
     }

     kit.run(*win);

     return 0;
}

This is drawingArea.ui:
<?xml version="1.0" encoding="UTF-8"?>
<interface>
<requires lib="gtk+" version="2.16"/>
<!-- interface-naming-policy project-wide -->
<object class="GtkWindow" id="window1">
<child>
<object class="GtkDrawingArea" id="drawingarea1"/>
</child>
</object>
</interface>

I experienced with a simple print that I do not enter the
on_expose_event() method.
Can anyone tell me where am I wrong?

Thanks in advance!

--
Alessandro Candini

MEEO S.r.l.
Via Saragat 9
I-44122 Ferrara, Italy
Tel: +39 0532 1861501
Fax: +39 0532 1861637
http://www.meeo.it

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