สอบถามเรื่อง DispatcherTimer ใน WPF VISUAL C# 2010 ครับ

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using Microsoft.Phone.Controls;
using System.Windows.Threading;
using Microsoft.Phone.Shell;
using System.Windows.Media.Imaging;

namespace PhoneAppCS
{
    public partial class MainPage : PhoneApplicationPage
    {

        // Constructor
        public MainPage()
        {
            InitializeComponent();
            dt.Interval = new TimeSpan(0, 0, 0, 0, 1000);
            dt.Tick += new System.EventHandler(this.dt_Tick);
            dt.Start();

        }

        private DispatcherTimer dt = new DispatcherTimer();

        private void dt_Tick(object sender, EventArgs e)
        {
            this.txtResult.Text = DateTime.Now.ToString();
        }
    }
}