public void UpdateDisplay(AObservable data)
 {
     TourData             = (GroupTour)data;
     lblTotalCost.Content = TourData.GetTotalCost();
     foreach (string location in TourData.GetLocations())
     {
         if (!lstvwlocations.Items.Contains(location))
         {
             lstvwlocations.Items.Add(location);
         }
     }
 }
 public void Update(AObservable subject)
 {
     UpdateDisplay(subject);
 }