[Vala] Why is my menubar not showing up?

[Fred van Zwieten <fvzwieten gmail com>]

Hi.

I try to make a menubar, taking examples from vala toolbar demo and a
pygtk tutorial. I have this sample code:

using Gtk;

class menusystem : Gtk.Window
{
    public menusystem ()
    {
        this.title = "Menu System Demo";
        this.destroy.connect (Gtk.main_quit);
        set_default_size (600, 600);
                                
        var menubar = new MenuBar();
        var file_menu = new Menu();
        var quit_item=new MenuItem.with_mnemonic("_Quit");
        file_menu.append(quit_item);
        quit_item.activate.connect(Gtk.main_quit);
        var file_launcher=new MenuItem.with_mnemonic("_File");
        file_launcher.set_submenu(file_menu);
        menubar.append(file_launcher);

        var vbox = new VBox (false, 0);
        vbox.pack_start (menubar,false,false,0);
        add (menubar);
    }

    static int main (string[] args)
    {
        Gtk.init (ref args);

        var mymenu = new menusystem ();
        mymenu.show_all();

        Gtk.main ();

        return 0;
    }
}

The menubar doesn't show up. Why not?

Greetz,
Fred