gtk--: Problem with Gtk_Pixmap!

[Oliver Freyd <freyd uni-muenster de>]

Now that I've upgraded to gtk+-0.99.4 and gtk--0.7.12 I have problems with
pixmaps. I just  tried to mape a little pixmap button class, 
so in it's creator I create a gdk_pixmap and then make a Gtk_Pixmap of it.

Only that 
 
  GtkWidget * widget =GTK_WIDGET(gtkobject);
  pixmap = gdk_pixmap_create_from_xpm (widget->window, &mask,
                                         &style->bg[GTK_STATE_NORMAL],
                                         "3DRings.xpm");
 
now gives a warning that "window!=NULL".

Then you don't get a pixmap on the button and when you press it,
the program crashes!

This did't happen in gtk+-0.99.3.
The question is now: How  do I get the GdkWindow of my button
when it gets defined only later. Should I  have to fiddle with the 
expose handler or something. 
I've even tried to show the main window immediately, and then put
in the other objects, but still the same result.

Any hints?!

bye,
  Oliver