[Vala] 0.7 signal syntax

[lode leroy <lode leroy gmail com>]

in http://live.gnome.org/Vala/CairoSample

I try replacing the line
        drawing_area.expose_event += this.on_expose;
with
        drawing_area.expose_event.connect(this.on_expose);

but this gives an error... could anyone enlighten me on what is the
correct syntax?

-- lode