main.vala

using Gtk;

namespace GraniteHello {

    public class GraniteHello : Granite.Application {

        public Window m_window;

        construct {
            program_name = "GraniteHello";
            exec_name = "granitehello";
            app_years = "2013";
            app_icon = "application-default-icon";
            app_launcher = "granite_hello.desktop";
            application_id = "org.elementary.granitehello";
            main_url = "http://www.ejweb.com.br/";
            bug_url = "http://www.ejweb.com.br/bugs/";
            help_url = "http://www.ejweb.com.br/help/";
            translate_url = "http://www.ejweb.com.br/translate/";
            /* about_authors = {"Your Girl <em>"};
               about_documenters = {"Your <em>"};
               about_artists = {"eu <em@e>"};
               about_comments = {"Edu translator!"};
               about_translators = {"tetss de tra."};
            */
            //also License.GPL_2_0 and License.GPL_3_0
            about_license_type = License.GPL_3_0;
        }

        public GraniteHello(){
            // For example if we wanted to use a dark theme.
            // Gtk.Settings.get_default ().gtk_application_prefer_dark_theme = true;
        }

        public override void activate (){
            this.m_window = new Window();
            this.m_window.set_default_size(800, 600);
            this.m_window.set_application(this);
            var button = new Button.with_label ("Oh Boy!");

            button.clicked.connect(() => {
                button.label = "Thank you!";
            });

            this.m_window.add(button);
            this.m_window.show_all();
        }
    }
}

public static int main(string[] args){

    Gtk.init(ref args);
    var GraniteHello = new GraniteHello.GraniteHello();
    return GraniteHello.run(args);

}