gistfile1.vala

// compile using valac app.vala -o app --pkg gtk+-2.0

using Gtk;

namespace MyApp
{
    class MyApp: Gtk.Window
    {
        public MyApp()
        {
            this.set_default_size(100, 100);
            
            var button = new Button.with_label("Click me!");
            add(button);
            
            button.clicked.connect(this.on_button_clicked);
        }
        
        private void on_button_clicked(Button button)
        {
            stdout.printf("Button clicked!\n");
        }
        
        public static int main(string[] args)
        {
            Gtk.init(ref args);
            
            var app = new MyApp();
            app.show_all();
            
            app.destroy.connect(Gtk.main_quit);
            
            Gtk.main();
            return 0;
        }
    }
}