/*
  * Creates or updates customer, and closes dialog.
  */
 private void btnSave_Click(object sender, RoutedEventArgs e)
 {
     if (areAllValuesValid())
     {
         if (mFacade.IsACustomerLoaded()) // update current customer
         {
             mFacade.UpdateCurrentCustomer(txtCustName.Text,
                                           txtCustAddress.Text);
         }
         else // create a new customer
         {
             mFacade.CreateCustomer(txtCustName.Text,
                                    txtCustAddress.Text);
         }
         this.Close();
     }
 }