Gtk+ g_signal_connect erro

olá pessoal estou com um problema quando vou compilar esse código;

class Form

{

	private:

	GtkWidget *widget;

        int OnClose(GtkWidget *widget, gpointer data);



	public:

	Form();

};



Form::Form()

{

   g_signal_connect(G_OBJECT(this->widget), "delete_event",

      G_CALLBACK(this->OnClose), NULL);

}

 

o erro:
sgtk.cc:136: error: invalid use of member (did you forget the ‘&’ ?)

eu ja coloquei o & mas deu outro erro:
sgtk.cc:136: error: ISO C++ forbids taking the address of a bound member function to form a pointer to member function. Say ‘&Form::OnClose’