我正在使用HttpWebRequest来调用Web服务。如果BeginGetResponse的AsyncCallback抛出错误,我想将它传播到我的主程序流程。我在执行此操作时遇到问题,因为错误不会传播到AsyncCallback之外。我已经尝试在HttpWebRequest链的每一步放置try / catch块,但它从未传播到“ResponseCallBack”方法之外。是否有可能将其恢复到主线程?
private void StartRequest()
{
// Code to create request object is here
// ...
httpRequest.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), httpRequest);
}
private void GetRequestStreamCallback(IAsyncResult result)
{
HttpWebRequest request = (HttpWebRequest)result.AsyncState;
// End the operation
var postStream = request.EndGetRequestStream(result);
string body = GenerateRequestBody();
// Convert the string into a byte array
byte[] postBytes = Encoding.UTF8.GetBytes(body);
// Write to request stream
postStream.Write(postBytes, 0, postBytes.Length);
postStream.Close();
// Start the asynchronous operation to get the resonse
try
{
request.BeginGetResponse(new AsyncCallback(ResponseCallback), request);
}
catch (Exception)
{
throw;
}
}
private void ResponseCallback(IAsyncResult result)
{
string contents = String.Empty;
HttpWebRequest request = (HttpWebRequest)result.AsyncState;
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(result);
using (Stream stream = response.GetResponseStream())
using (StreamReader reader = new StreamReader(stream))
{
contents = reader.ReadToEnd();
}
// Check the status
if (response.StatusCode == HttpStatusCode.OK)
{
//EXCEPTION NEVER MAKES IT PASSED HERE, EVEN IF I HAVE IT IN A TRY/CATCH BLOCK AND RE-THROW IT.
_object = ProcessResponseEntity(contents);
}
}
答案 0 :(得分:2)
我认为你对异步代码exectution的工作方式以及回调执行如何适应调用代码感到困惑。
在GetRequestStreamCallback
内,在调用request.BeginGetResponse
后,该方法将继续执行,并在您的示例中结束。
不知道何时(或者甚至)ResponseCallback
将在UI线程上执行或将发生什么。因此,ResponseCallback
将在不同的线程上执行。
使用Dispatcher.BeginInvoke
可以在UI线程上运行回调中的代码(您需要与UI进行交互)。但是,您无法在另一种方法的上下文中执行此操作。
虽然我不推荐它,但您可能需要查看this discussion以使回调看起来同步执行。这将阻止您的UI线程,因此不建议这样做。