Simple Gtk.Application example in vala

main.vala

using Gtk;

public class MyApplication : Gtk.Application {

	public MyApplication () {
		Object(application_id: "testing.my.application",
				flags: ApplicationFlags.FLAGS_NONE);
	}

	protected override void activate () {

	// Create the window of this application and show it
	Gtk.ApplicationWindow window = new Gtk.ApplicationWindow (this);
	window.set_default_size (800, 600);
	window.window_position = WindowPosition.CENTER;
	window.set_border_width(10);

	// add headerbar with button
	Gtk.HeaderBar headerbar = new Gtk.HeaderBar();
        headerbar.show_close_button = true;
        headerbar.title = "Window";
        window.set_titlebar(headerbar);

        Gtk.Button button = new Gtk.Button.with_label ("About");
        button.clicked.connect ( () =>{
        	// show about dialog on click
        	string[] authors = { "GNOME Documentation Team", null };
		string[] documenters = { "GNOME Documentation Team", null };

		Gtk.show_about_dialog (window,
	                               "program-name", ("GtkApplication Example"),
	                               "copyright", ("Copyright \xc2\xa9 2012 GNOME Documentation Team"),
	                               "authors", authors,
	                               "documenters", documenters,
	                               "website", "http://developer.gnome.org",
	                               "website-label", ("GNOME Developer Website"),
	                               null);
        });
        // add button to headerbar
        headerbar.pack_end(button);

        // create stack
	Gtk.Stack stack = new Gtk.Stack();
	stack.set_transition_type(Gtk.StackTransitionType.SLIDE_LEFT_RIGHT);

	// giving widgets to stack
        Gtk.Label label = new Gtk.Label("");
        label.set_markup("<big>A label</big>");
        stack.add_titled(label, "label", "A label");

        Gtk.Label label2 = new Gtk.Label("");
        label2.set_markup("<big>Another label</big>");
        stack.add_titled(label2, "label2", "Another label");

        // add stack(contains widgets) to stackswitcher widget
        Gtk.StackSwitcher stack_switcher = new Gtk.StackSwitcher();
        stack_switcher.halign = Gtk.Align.CENTER;
        stack_switcher.set_stack(stack);

        // add stackswitcher to vertical box
        Gtk.Box vbox = new Gtk.Box(Gtk.Orientation.VERTICAL, 0);
        vbox.pack_start(stack_switcher, false, false, 0);
        vbox.pack_start(stack, false, false, 10);

        window.add(vbox);
	        window.show_all ();
	}

	public static int main (string[] args) {
		MyApplication app = new MyApplication ();
		return app.run (args);
	}
}