Example: IconInfo

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

// Add a button
Gtk.Button button = new Gtk.Button ();
this.add (button);

// Get the icon:
Gtk.IconTheme icon_theme = Gtk.IconTheme.get_default ();
try {
Gtk.IconInfo? icon_info = icon_theme.lookup_icon ("go-home", 48, 0);
assert (icon_info != null);

Gdk.Pixbuf pixbuf = icon_info.load_icon ();
button.image = new Gtk.Image.from_pixbuf (pixbuf);
} catch (Error e) {
warning (e.message);
}
}

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.IconInfo.vala

See: