private void PostCode_OnKeyDown(object sender, KeyEventArgs e)
 {
     if (e.Key == Key.Enter)
     {
         if (ReceiverForm.Visibility == Visibility.Visible)
         {
             if (NameLabel.Visibility == Visibility.Visible)
             {
                 NameLabel.Focus();
             }
             else if (EmailLabel.Visibility == Visibility.Visible)
             {
                 EmailLabel.Focus();
             }
             else if (Phone.Visibility == Visibility.Visible)
             {
                 PCode.Focus();
                 PCode.Select(PCode.Text.Length, 0);
             }
             else
             {
                 ViewModel.Validate();
             }
         }
         else
         {
             ViewModel.Validate();
         }
     }
 }