Creating a Sortable Filter

Hello, This picks up where I left off in the thread "cannot create gtksourcestylesheme interface". I'll briefly restate: I was using a GtkTreeView with a GtkListStore data model. I wrapped the GtkListStore in a GtkTreeModelFilter to use the filtering capabilities but this lost the sorting ability because GtkTreeModelFilter does not implement the GtkTreeSortable interface. I wrote a simple class that extends GtkTreeModelFilter and implements GtkTreeSortable and simply calls the underlying model's (in my case GtkListStore) GtkTreeSortable methods. Gtk+ does not recognize my new class as sortable although I implement GtkTreeSortable and implement all of its methods. I get the following errors when an attempt at sorting is initiated: ---------- Gtk-CRITICAL **: gtk_tree_sortable_get_sort_column_id: assertion `GTK_IS_TREE_SORTABLE (sortable)' failed Gtk-CRITICAL **: gtk_tree_sortable_has_default_sort_func: assertion `GTK_IS_TREE_SORTABLE (sortable)' failed Gtk-CRITICAL **: gtk_tree_sortable_set_sort_column_id: assertion `GTK_IS_TREE_SORTABLE (sortable)' failed ---------- These are the same errors I get if my model is a GtkTreeModelFilter object (or I imagine any model that does not implement GtkTreeSortable). The filtering behavior is unchanged and Gtk+ does not balk at the new object for purposes of GtkTreeModel behavior. So, it appears to extend GtkTreeModelFilter in the manner I would expect but does not gain the GtkTreeSortable properties. So, are there any requirements for passing the GTK_IS_TREE_SORTABLE assertion besides implementing the GtkTreeSortable interface? Maybe more to the point, can I truly implement the interface in PHP in a way that C will recognize? Is the successful recognition of my new class as a GtkTreeModel because that interface was already implemented by it (equivalently, I realize C is not object-oriented) in C? Thanks for your time. -Jake Cobb