Web客户端的DownloadStringCompleted事件处理程序永远不会调用

问题描述

我试图让使用Web客户端异步HTTP GET请求，但是，注册的回调不会被调用。我也试着与同步之一，它工作得很好。我究竟做错了什么？

  Web客户端asyncWebRequest;
公共AsyncWebRequest（URI链接）
{
    asyncWebRequest =新的Web客户端（）;
    URL =新的URI（http://www.google.com/）;
    //字符串测试= asyncWebRequest.DownloadString（URL）; //这个工程
    asyncWebRequest.DownloadStringCompleted + =新DownloadStringCompletedEventHandler（asyncWebRequest_DownloadStringCompleted）;
    asyncWebRequest.DownloadStringAsync（URL）;
}

无效asyncWebRequest_DownloadStringCompleted（对象发件人，DownloadStringCompletedEventArgs E）
{
    抛出新的NotImplementedException（）;
}
 

解决方案

也许是因为你处置 Web客户端才下载完。在code执行不上停止asyncWebRequest.DownloadStringAsync（URL）; 和你处置 Web客户端对象通过关闭using语句。

尝试处置 Web客户端在 asyncWebRequest_DownloadStringCompleted 。

结果

I'm trying to make an asynchronous HTTP GET request using Webclient, however, the registered callback never gets called. I've also tried with the sync one, and it worked fine. What am I doing wrong?

WebClient asyncWebRequest;
public AsyncWebRequest(Uri url)
{
    asyncWebRequest = new WebClient();
    url = new Uri("http://www.google.com/");
    // string test = asyncWebRequest.DownloadString(url);  // this works
    asyncWebRequest.DownloadStringCompleted += new DownloadStringCompletedEventHandler(asyncWebRequest_DownloadStringCompleted);
    asyncWebRequest.DownloadStringAsync(url);
}

void asyncWebRequest_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
{
    throw new NotImplementedException();
}

解决方案

Maybe because you disposing the WebClient before it finished downloading. The code execution don't stop on asyncWebRequest.DownloadStringAsync(url); and you are disposing the WebClient object by closing the using statement.

try to dispose the WebClient on asyncWebRequest_DownloadStringCompleted.

results

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