[gtkada] help on a draw program

[User MARTIN]

hi all i try to learn how to use gtkada to make some draw i have make a
litle program who use the code for draw found in the gtkada RM
and a bit of code of myself but...
no luck not working and as i'm a begginer in gtkada i have spend a nice
day trying to make it work.
so i send all the stuff here , and i hope that someone can take the time
to either explain me the matter or send me a link to a simple gtkada
program who use draw.

the code is :

with Gtk.Main, Gtk.Window, Draw, Gtk.Drawing_Area, Gtk.Widget,
Gtk.Handlers;
 with Ada.Text_IO;
use Gtk.Widget;
procedure dessintest is
   Window : Gtk.Window.Gtk_Window;
   Drawing_Area : Gtk.Drawing_Area.Gtk_Drawing_Area;
begin
   Gtk.Main.Init;
   Gtk.Window.Gtk_New (Window);
   Gtk.Drawing_Area.Gtk_New (Drawing_Area);
   Gtk.Window.Add(Window, Drawing_Area);
--   Handlers.Connect     (Drawing_Area, "expose_event",
Handlers.To_Marshaller (Expose_Event'Access));
   Draw(Drawing_Area);
   Gtk.Drawing_area.Show(Drawing_Area);
   Gtk.Window.Show (Window);
   Gtk.Main.Main;
end dessintest;

after compil i get :

Gdk-CRITICAL **: file gdkwindow.c: line 929 (gdk_window_clear): assertion
`window != NULL' failed.

Gdk-CRITICAL **: file gdkgc.c: line 51 (gdk_gc_new_with_values): assertion
`window != NULL' failed.

Gdk-CRITICAL **: file gdkdraw.c: line 65 (gdk_draw_line): assertion
`drawable != NULL' failed.

Gdk-CRITICAL **: file gdkdraw.c: line 124 (gdk_draw_arc): assertion
`drawable != NULL' failed.

Gdk-CRITICAL **: file gdkdraw.c: line 268 (gdk_draw_text): assertion
`drawable != NULL' failed.

Gdk-CRITICAL **: file gdkgc.c: line 288 (gdk_gc_unref): assertion `gc !=
NULL' failed.

the draw function can be found at:

http://libre.act-europe.fr/GtkAda/docs/gtkada_rm_30.html#SEC115

thanks all if u can spend  a litle time on that or even giving me some
way to understood what this don't works.