C# WPF Threading

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Threading;
using System.Threading;

namespace WpfThreading
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private delegate void SimpleDelegate();

        public MainWindow()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            SimpleDelegate del = new SimpleDelegate(countDown);
            del.BeginInvoke(null, null);//This is called on UI thread, can Invoke directly
        }

        private void countDown()
        {
            for (int i = 5; i >= 0; i--)
            {
                SimpleDelegate del = delegate()
                { this.label1.Content = i; };
                this.Dispatcher.BeginInvoke(DispatcherPriority.Send, del);//Called on the Worker thread, have to Invoke from the dispatcher's standpoint

                //Console.WriteLine(i);
                Thread.Sleep(1000);
            }
        }
    }
}