WPF ListCtrl滚动到底部

ResultListCtrl.Dispatcher.BeginInvoke(
    new Action(() => { 
        ResultListCtrl.Items.Add(str);

        if (VisualTreeHelper.GetChildrenCount(ResultListCtrl) > 0)
        {
            Border border = (Border)VisualTreeHelper.GetChild(ResultListCtrl, 0);
            ScrollViewer scrollViewer = (ScrollViewer)VisualTreeHelper.GetChild(border, 0);
            scrollViewer.ScrollToBottom();
        }
    }),
    null);
    Thread.Sleep(200);
}