Example: Spinner

public class Application : Gtk.Window {
public Application () {
// Prepare Gtk.Window:
this.title = "My Gtk.Spinner";
this.window_position = Gtk.WindowPosition.CENTER;
this.destroy.connect (Gtk.main_quit);
this.set_default_size (400, 400);

// Create & add a new spinner:
Gtk.Spinner spinner = new Gtk.Spinner ();
spinner.active = true;
this.add (spinner);
}

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

Application app = new Application ();
app.show_all ();
Gtk.main ();
return 0;
}
}

 valac --pkg gtk+-3.0 Gtk.Spinner.vala

See: