c# – 如何从方法外部获得异步Web请求的响应？

发布时间：2020-12-15 17:24:53 所属栏目：百科来源：网络整理

导读：我有点困惑.我试图以异步方式发布到我的Web服务,理想情况下我想启动请求,在UI上显示加载微调器,然后当异步请求完成处理响应时,如果有响应则显示错误,或者用结果做另一个操作. 这是我的代码,我在这里调用请求并传递一些数据. private void SignInExecute(){ i

我有点困惑.我试图以异步方式发布到我的Web服务,理想情况下我想启动请求,在UI上显示加载微调器,然后当异步请求完成处理响应时,如果有响应则显示错误,或者用结果做另一个操作.

这是我的代码,我在这里调用请求并传递一些数据.

private void SignInExecute()
{

        if (Username == null || Password == null)
        {
            LoginOutput = "Please provide a username or password.";
        }
        else
        {
            this.webService.SendLoginRequest("http://localhost:3000/client_sessions","username=" + Username + "&password=" + Password);

        }

}

这是实际的Web请求代码：

public void SendLoginRequest(string url,string postdata)
{
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);

        request.Method = "POST";

        request.ContentType = "application/x-www-form-urlencoded";

        request.Accept = "application/json";

        byte[] byteArray = Encoding.UTF8.GetBytes(postdata);

        request.CookieContainer = new CookieContainer();

        request.ContentLength = byteArray.Length;

        Stream dataStream = request.GetRequestStream();

        dataStream.Write(byteArray,byteArray.Length);

        dataStream.Close();

        ((HttpWebRequest)request).KeepAlive = false;

        request.BeginGetResponse(new AsyncCallback(GetLoginResponseCallback),request);


    }

    private static void GetLoginResponseCallback(IAsyncResult asynchronousResult)
    {
        HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;

        // End the operation
        HttpWebResponse response =  (HttpWebResponse)request.EndGetResponse(asynchronousResult);
        Stream streamResponse = response.GetResponseStream();
        StreamReader streamRead = new StreamReader(streamResponse);
        string responseString = streamRead.ReadToEnd();

        Console.WriteLine(responseString);

        // Close the stream object
        streamResponse.Close();
        streamRead.Close();
        response.Close();
    }

所以总结一下.我希望能够将响应返回给最初调用Web请求启动的对象.有帮助吗？

解决方法

您需要告诉BeginGetResponse返回到通过SynchronizationContext.Current调用它的相同上下文.像这样的东西(代码没有正确的错误检查,所以你应该正确考虑)(另外,Platinum Azure是正确的,你应该使用一个使你的流正常关闭(并保证)：

在您的SendLoginRequest中：

//Box your object state with the current thread context
object[] boxedItems = new []{request,SynchronizationContext.Current};
request.BeginGetResponse(new AsyncCallback(GetLoginResponseCallback),boxedItems);

getresponse代码：

private static void GetLoginResponseCallback(IAsyncResult asynchronousResult)
{
//MY UPDATE 
    //Unbox your object state with the current thread context
    object[] boxedItems = asynchronousResult.AsyncState as object[];
    HttpWebRequest request = boxedItems[0] as HttpWebRequest;
    SynchronizationContext context = boxedItems[1] as SynchronizationContext;

    // End the operation
    using(HttpWebResponse response =  
        (HttpWebResponse)request.EndGetResponse(asynchronousResult))
    {
        using(Stream streamResponse = response.GetResponseStream())
        {
            using(StreamReader streamRead = new StreamReader(streamResponse))
            {
                string responseString = streamRead.ReadToEnd();

                Console.WriteLine(responseString);
//MY UPDATE
                //Make an asynchronous call back onto the main UI thread 
                //(context.Send for a synchronous call)
                //Pass responseString as your method parameter 
                //If you have more than one object,you will have to box again
                context.Post(UIMethodToCall,responseString);
            }
        }
    }
}

实现UI处理

public static void UIMethodCall(object ObjectState)
{
    String response = ObjectState as String;
    label1.Text = String.Format("Output: {0}",response);
    //Or whatever you need to do in the UI...
}

现在,我会先测试一下这个.我对Microsoft实现事件驱动异步的理解是,响应是上下文感知的,并且知道返回哪个上下文.因此,在跳到假设您不在同一个上下文之前,通过尝试更新UI来测试它(如果您不在调用(UI)线程上,这将导致线程上下文异常)

（编辑：李大同）

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