Custom widgets with GtkBuilder

[Braden McDaniel <braden endoframe com>]

I posted this query to gtk-app-devel a couple of days ago; but so far it
has no takers. Hopefully someone here will have some insight...

I'm migrating some code from libglade to GtkBuilder.

I have inherited GtkFileChooserDialog in order to perform some setup
when creating it (i.e., set title, set the default response, and add
some filters). With libglade, I was performing this logic in a _new
function; I delegated to the _new function in the callback supplied to
glade_register_widget.

When migrating to GtkBuilder, I didn't find an equivalent of
glade_register_widget. I concluded that GtkBuilder must simply use
g_object_new and decided that the most convenient way to do the
initialization I want to do would be to move it to the _init function.
That function now looks like this:

        void
        openvrml_player_file_chooser_dialog_init(
            OpenvrmlPlayerFileChooserDialog * dialog)
        {
            gtk_dialog_add_buttons(GTK_DIALOG(dialog),
                                   GTK_STOCK_CANCEL, GTK_RESPONSE_CANCEL,
                                   GTK_STOCK_OPEN, GTK_RESPONSE_ACCEPT,
                                   NULL);
        
            gtk_dialog_set_default_response(GTK_DIALOG(dialog),
                                            GTK_RESPONSE_ACCEPT);
        
            GtkFileFilter * const world_filter = gtk_file_filter_new();
            g_return_if_fail(world_filter);
            scope_guard world_filter_guard = make_guard(g_object_unref,
                                                        world_filter);
            boost::ignore_unused_variable_warning(world_filter_guard);
            gtk_file_filter_set_name(world_filter, "VRML/X3D worlds");
            gtk_file_filter_add_mime_type(world_filter, "x-world/x-vrml");
            gtk_file_filter_add_mime_type(world_filter, "model/vrml");
            gtk_file_filter_add_mime_type(world_filter, "model/x3d+vrml");
        
            gtk_file_chooser_add_filter(GTK_FILE_CHOOSER(dialog), world_filter);
            world_filter_guard.dismiss();
        
            GtkFileFilter * const all_filter = gtk_file_filter_new();
            g_return_if_fail(all_filter);
            scope_guard all_filter_guard = make_guard(g_object_unref, all_filter);
            boost::ignore_unused_variable_warning(all_filter_guard);
            gtk_file_filter_set_name(all_filter, "All files");
            gtk_file_filter_add_pattern(all_filter, "*");
        
            gtk_file_chooser_add_filter(GTK_FILE_CHOOSER(dialog), all_filter);
            all_filter_guard.dismiss();
        }

But since moving the code and having GtkBuilder create the widget, I'm
now getting these assertion failures:

        (openvrml-player:25152): Gtk-CRITICAL **: gtk_file_chooser_add_filter: assertion `GTK_IS_FILE_CHOOSER (chooser)' failed
        
        (openvrml-player:25152): Gtk-CRITICAL **: gtk_file_chooser_add_filter: assertion `GTK_IS_FILE_CHOOSER (chooser)' failed
        
I have a feeling that I've overlooked something and GtkBuilder isn't
creating the widget correctly; any ideas?

-- 
Braden McDaniel                           e-mail: <braden endoframe com>
<http://endoframe.com>                    Jabber: <braden jabber org>