/*
  * Updates guest details according to window TextBoxes contents.
  */
 private void updateGuest()
 {
     if (!this.isCustomer) // edit current guest
     {
         mFacade.EditGuest(guestIndex,
                           txtName.Text,
                           txtPassportNb.Text,
                           Int32.Parse(txtAge.Text));
     }
     else // edit current customer's guest properties
     {
         mFacade.EditCustomerGuestDetails(guestIndex,
                                          txtPassportNb.Text,
                                          Int32.Parse(txtAge.Text));
     }
 }