gtk-hello.vala - gnome-shell CPU usage example

// gtk-hello.vala:
// valac --pkg gtk+-3.0 gtk-hello.vala
using Gtk;

class HelloWindow : Gtk.Window {
    public HelloWindow() {
        this.title = "First GTK+ Program";
        this.border_width = 10;
        this.window_position = WindowPosition.CENTER;
        this.set_default_size (350, 70);

        var button = new Button.with_label ("Click me!");
        button.clicked.connect (() => {
            button.label = "Thank you";
        });

        this.add (button);

        this.add_tick_callback(() => {
            DateTime now = new DateTime.now(new TimeZone.utc());
            //print(now.format("%T - Redrawing\n"));
            this.queue_draw();
            return true;
        });
    }

    public override bool draw(Cairo.Context cr) {
        return base.draw(cr);
    }
}

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

    var window = new HelloWindow ();
    window.destroy.connect (Gtk.main_quit);
    window.show_all ();

    Gtk.main ();
    return 0;
}