效果：
UI：放置一個Label ---><Label Name="lblSecond" FontSize="20" Foreground="Red" ></Label>
CS：
private int countSecond=300; //記錄秒數
private void UserControl_Loaded(object sender, RoutedEventArgs e)
{
private DispatcherTimer disTimer = new DispatcherTimer();
disTimer.Interval = new TimeSpan(0, 0, 0, 1); //參數分別為：天，小時，分，秒。此方法有重載，可根據實際情況調用。
disTimer.Tick += new EventHandler(disTimer_Tick); //每一秒執行的方法
disTimer.Start();
}
void disTimer_Tick(object sender, EventArgs e)
{
if(countSecond==0)
{
MessageBox.Show("結束");
}
else
{
//判斷lblSecond是否處於UI線程上
if (lblSecond.Dispatcher.CheckAccess())
{
lblSecond.Content=countSecnd.ToString();
}
else
{
lblSecond.Dispatcher.BeginInvoke(DispatcherPriority.Normal,(Action)(() =>{
lblSecond.Content=countSecond.ToString();
}));
}
countSecond--;
}
}