public override void RowSelected(UITableView tableView, NSIndexPath indexPath)
        {
            var shippingRate = shippingRates [indexPath.Row];

            checkout.ShippingRate = shippingRate;

            client.UpdateCheckout (checkout, (checkout, error) => {
                if (error == null && checkout != null) {
                    var preCheckoutController = new PreCheckoutViewController (client, checkout);
                    preCheckoutController.CurrencyFormatter = currencyFormatter;
                    NavigationController.PushViewController (preCheckoutController, true);
                } else {
                    Console.WriteLine ("Error applying checkout: {0}", error);
                }
            });
        }
        public async override void RowSelected(UITableView tableView, NSIndexPath indexPath)
        {
            checkout.ShippingRate = shippingRates[indexPath.Row];

            try
            {
                checkout = await client.UpdateCheckoutAsync(checkout);

                var preCheckoutController = new PreCheckoutViewController(client, checkout);
                preCheckoutController.CurrencyFormatter = currencyFormatter;
                NavigationController.PushViewController(preCheckoutController, true);
            }
            catch (NSErrorException ex)
            {
                Console.WriteLine("Error applying checkout: {0}", ex.Error);
            }
        }
        public override void RowSelected(UITableView tableView, NSIndexPath indexPath)
        {
            var shippingRate = shippingRates [indexPath.Row];

            checkout.ShippingRate = shippingRate;

            client.UpdateCheckout(checkout, (checkout, error) => {
                if (error == null && checkout != null)
                {
                    var preCheckoutController = new PreCheckoutViewController(client, checkout);
                    preCheckoutController.CurrencyFormatter = currencyFormatter;
                    NavigationController.PushViewController(preCheckoutController, true);
                }
                else
                {
                    Console.WriteLine("Error applying checkout: {0}", error);
                }
            });
        }