مشكل ابتدايي در GTK Sharp

[davood_skh]

سلام
من در monodevelop كد زير را نوشتم ولي هيچ كدام از كلاسهاي window و label را نمي شناسه
كمك كنيد.
using System;
using Gtk;

public class GtkHelloWorld
{

public static void Main()
{
Application.Init();

//Create the Window
Window myWin = new Window("My first GTK# Application! ");
myWin.Resize(200,200);

//Create a label and put some text in it.
Label myLabel = new Label();
myLabel.Text = "Hello World!!!!";

//Add the label to the form
myWin.Add(myLabel);

//Show Everything
myWin.ShowAll();

Application.Run();
}
}