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尝试实现一个 WebRequest 并同步返回给调用者。我尝试了各种实现，我认为这是迄今为止最合适的。

不幸的是，下面的代码抛出了InvalidOperationException一条消息

每次异步操作只能调用一次 EndGetResponse

我真的很努力才能做到这一点，这对于我构建的库来说非常重要，以便像这样使用 WebRequest。

以下代码打算在 Windows Phone 8 和 Windows 8 平台中使用。

我已经了解并使用了 async/await 模式，但在我的库的一部分中使用 Web 服务请求的同步版本对我来说非常重要。

编码：

public void ExecuteRequest(string url, string requestData)
{
        WebRequest request = WebRequest.Create(new Uri(url));
        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";
        request.Headers["Header-Key"] = "AKey";

        DTOWebRequest webRequestState = new DTOWebRequest
        {
            Data = requestData,
            Request = request
        };

        ManualResetEventSlim resetEventSlim = new ManualResetEventSlim(false);

        // Begin the request using a delegate
        request.BeginGetRequestStream(ar =>
        {
            DTOWebRequest requestDataObj = (DTOWebRequest )ar.AsyncState;
            HttpWebRequest requestStream = (HttpWebRequest)requestDataObj.Request;

            string data = requestDataObj.Data;

            // Convert the string into a byte array.
            byte[] postBytes = Encoding.UTF8.GetBytes(data);

            try
            {
                // End the operation
                using (Stream endGetRequestStream = requestStream.EndGetRequestStream(ar))
                {
                    // Write to the request stream.
                    endGetRequestStream.Write(postBytes, 0, postBytes.Length);
                }

                // Get the response using a delegate
                requestStream.BeginGetResponse(result =>
                {
                    DTOWebRequest requestDataObjResult = (DTOWebRequest )ar.AsyncState;
                    HttpWebRequest requestResult = (HttpWebRequest)requestDataObjResult.Request;

                    try
                    {
                        // End the operation
                        using (HttpWebResponse response = (HttpWebResponse)requestResult.EndGetResponse(ar)) // Here the exception is thrown.
                        {
                            HttpStatusCode rcode = response.StatusCode;
                            Stream streamResponse = response.GetResponseStream();
                            StreamReader streamRead = new StreamReader(streamResponse);

                            // The Response
                            string responseString = streamRead.ReadToEnd();

                            if (!string.IsNullOrWhiteSpace(requestDataObjResult.FileName))
                            {
                                FileRepository fileRepo = new FileRepository();
                                fileRepo.Delete(requestDataObjResult.FileName);
                            }

                            Debug.WriteLine("Response : {0}", responseString);
                        }
                    }
                    catch (WebException webEx)
                    {
                        WebExceptionStatus status = webEx.Status;
                        WebResponse responseEx = webEx.Response;
                        Debug.WriteLine(webEx.ToString());
                    }

                    resetEventSlim.Set(); // Signal to return handler
                }, requestDataObj);
            }
            catch (WebException webEx)
            {
                WebExceptionStatus status = webEx.Status;
                WebResponse responseEx = webEx.Response;
                Debug.WriteLine(webEx.ToString());
            }    
        }, webRequestState);

        resetEventSlim.Wait(5000); // Wait either for Set() or a timeout 5 secs.
    }
}

谢谢你。

4

1 回答 1

1

您不能在 Windows Phone 中进行同步 Web 呼叫，这就是您不能这样做的原因。

如果你是，你会打电话GetRequestStream而不是BeginGetRequestStram/ EndGetRequestStream。

在 Windows Phone 上同步的唯一原因是阻止 UI，这是一个非常糟糕的主意。

您应该改用 anHttpClient和 àsync-await`。

但是如果你真的认为你应该（并且可以）在 Windows Phone 上进行异步调用，你总是可以尝试这样的事情：

public void ExecuteRequest(string url, string requestData)
{
    try
    {
        WebRequest request = WebRequest.Create(new Uri(url));
        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";
        request.Headers["Header-Key"] = "AKey";

        // Convert the string into a byte array.
        byte[] postBytes = Encoding.UTF8.GetBytes(requestData);

        using (var requestStream = request.EndGetRequestStream(request.BeginGetRequestStream(null, null)))
        {
            // Write to the request stream.
            endGetRequestStream.Write(postBytes, 0, postBytes.Length);
        }

        using (var response = request.EndGetResponse(request.BeginGetResponse(null, null)))
        {
            using (var streamRead = new StreamReader(response.GetResponseStream()))
            {
                // The Response
                string responseString = streamRead.ReadToEnd();

                if (!string.IsNullOrWhiteSpace(requestDataObjResult.FileName))
                {
                    var fileRepo = new FileRepository();
                    fileRepo.Delete(request.FileName);
                }

                Debug.WriteLine("Response : {0}", responseString);
            }
        }
    }
    catch (WebException webEx)
    {
        WebExceptionStatus status = webEx.Status;
        WebResponse responseEx = webEx.Response;
        Debug.WriteLine(webEx.ToString());
    }    
}

但我真的认为你应该修改你的决定/需要。

于 2013-09-08T22:33:16.940 回答