public IAsyncResult BeginGetShippingRatesAsync(decimal weight, string originZipCode, string destinationZipCode, AsyncCallback callback, object state)
{
// create object that will store results
AsyncResult<ShippingRate[]> asyncResult = new AsyncResult<ShippingRate[]>(callback, state);
ShippingRatesRequest request = new ShippingRatesRequest(asyncResult, 3);
// launch asynchronous requests, which will complete in parallel
WebRequest fedExRequest = CreateFedExRequest(weight, originZipCode, destinationZipCode);
fedExRequest.BeginGetResponse(ar => FedExCallback(request, fedExRequest, ar), null);
WebRequest upsRequest = CreateUpsRequest(weight, originZipCode, destinationZipCode);
upsRequest.BeginGetResponse(ar => UpsCallback(request, upsRequest, ar), null);
WebRequest uspsRequest = CreateUspsRequest(weight, originZipCode, destinationZipCode);
uspsRequest.BeginGetResponse(ar => UspsCallback(request, uspsRequest, ar), null);
// return IAsyncResult implementation to client
return asyncResult;
}
private static void UpsCallback(ShippingRatesRequest request, WebRequest webRequest, IAsyncResult asyncResult)
{
using (WebResponse response = webRequest.EndGetResponse(asyncResult))
request.AddRates(GetUpsRates(response));
}