private void AddGuestRequestButton_Click(object sender, RoutedEventArgs e)
 {
     foreach (var item in AddRequest.Children)
     {
         if (item is ComboBox)
         {
             if (((ComboBox)item).SelectedItem == null)
             {
                 MessageBox.Show("לא מולאו כל השדות");
                 return;
             }
         }
     }
     if (entryDateDatePicker.SelectedDate != null)
     {
         guest.EntryDate = ((DateTime)entryDateDatePicker.SelectedDate);
     }
     if (releaseDateDatePicker.SelectedDate != null)
     {
         guest.ReleaseDate = ((DateTime)releaseDateDatePicker.SelectedDate);
     }
     try
     {
         guest.GuestRequestKey = bl.AddGuestRequest(this.guest);
     }
     catch (DuplicateWaitObjectException exp)
     {
         MessageBox.Show(exp.Message);
         return;
     }
     catch (ArgumentOutOfRangeException exp)
     {
         MessageBox.Show(exp.Message);
         return;
     }
     catch
     {
         MessageBox.Show("שגיאה לא ידועה");
         return;
     }
     guest.GuestRequestKey = 0;//for next round
     MessageBox.Show("הבקשה התווספה בהצלחה");
     this.Client = bl.GetClient(clientID);
     this.listBox.ItemsSource = Client.Requests;
     this.listBox.Items.Refresh();
     NavigationService.GoBack();
 }