// Add the discount code to the checkout and update the order summary when the request completes.
 private void SetDiscountCode(string discountCode)
 {
     ShowLoadingDialog(Resource.String.syncing_data);
     SampleApplication.SetDiscountCode(discountCode,
                                       delegate
     {
         DismissLoadingDialog();
         UpdateOrderSummary();
     },
                                       delegate
     {
         DismissLoadingDialog();
         Toast.MakeText(this, GetString(Resource.String.discount_error, discountCode), ToastLength.Long).Show();
     });
 }