private void RefreshTick()
 {
     if (cUrl != url)
     {
         if (cUrl == "refresh")
         {
             ScreenView.Refresh();
             lock (cUrl) cUrl = url;
         }
         else
         {
             ScreenView.Navigate(new Uri(cUrl));
             localSettings.Values["url"] = cUrl;
             lock (cUrl) url = cUrl;
         }
     }
 }