[Vala] How to override a "class closure for a signal"?

[Michael Gratton <mike vee net>]

Hey all,

I have a subclass of Gtk.ListBox and I'm trying to override 
Gtk.Container::gtk_container_set_focus_child on it to prevent its 
default behaviour of automatically scrolling to the new focus child. 
The docs for that method say this:

> This function emits the GtkContainer::set_focus_child signal of 
> container. Implementations of GtkContainer can override the default 
> behaviour by overriding the class closure of this signal.

How exactly do I do that? I tried overriding the method using:

> public override void set_focus_child(Gtk.Widget? child) { ... }

But even if I do not chain up using a call to 
"base.set_focus_child(child)", it seems Gtk.Container's method is still 
invoked.

I also tried overriding the signal body using variously:

> public override signal void set_focus_child(Gtk.Widget? child) { ... }
> public new signal void set_focus_child(Gtk.Widget? child) { ... }

But then valac complains that it "hides inherited signal" in the first 
case and "Only virtual signals can have a default signal handler body" 
for both.

Any hints? Thanks!

//Mike

--
⊨ Michael Gratton, Percept Wrangler.
⚙ <http://mjog.vee.net/>