C# WebRequest-为多个请求异步检索数据

代码不完整（未生成），因为我无法在writeResponseTA（）中获取下一行中的“项”

我一定错过了什么。请指出

以下是完整的代码：-

static string[] imageUris =
        { "http://www.cricinfo.com/db/PICTURES/CMS/118200/118217.2.jpg",
        "http://www.cricinfo.com/db/PICTURES/CMS/117500/117599.2.jpg",
        "http://www.cricinfo.com/db/PICTURES/CMS/117500/117598.2.jpg",
        "http://www.cricinfo.com/db/PICTURES/CMS/106400/106412.2.jpg",
        "http://www.cricinfo.com/db/PICTURES/CMS/106400/106411.2.jpg",
        "http://www.cricinfo.com/db/PICTURES/CMS/106200/106275.2.jpg",
        "http://www.cricinfo.com/db/PICTURES/CMS/106300/106362.2.jpg"
        };

        static void Main(string[] args)
        {
            SendAsynchronousRequests();
            Console.WriteLine("All the files have been requested and retrieved...");
            Console.ReadLine();
        }



static void SendAsynchronousRequests()
        {
            WebRequest[] requests = InitializeWebRequests();
            foreach (var item in requests)
            {
                Console.WriteLine("Trying to retrieve :-" + item.RequestUri.OriginalString);
                item.BeginGetResponse
                (
                   WriteResponseData,
                );
             }

        }

    static WebRequest[] InitializeWebRequests()
    {
        WebRequest[] requests = new WebRequest[imageUris.Length];
        int temp = 0;
        foreach (var item in imageUris)
        {
            requests[temp] = WebRequest.Create(item);
            //requests[temp].Method = "GET";
            temp++;
        }
        return requests;
    }
    static void WriteResponseData(IAsyncResult result)
    {
        HttpWebResponse WebResp = (HttpWebResponse)item.EndGetResponse(result);
        Console.WriteLine("WebResp.StatusCode :-" + WebResp.StatusCode);
        Console.WriteLine("WebResp.Server :- " + WebResp.Server);
        Console.WriteLine("WebResp.ContentLength :- " + WebResp.ContentLength.ToString());
        Console.WriteLine(Environment.NewLine);

    }

编辑

因此，该方法（将编译）的修改代码如下：-

WebRequest request = (WebRequest)result.AsyncState;
            if (result != null && result.IsCompleted)
            {
                HttpWebResponse WebResp = (HttpWebResponse)request.EndGetResponse(result);
                Console.WriteLine("WebResp.StatusCode :-" + WebResp.StatusCode);
                Console.WriteLine("WebResp.Server :- " + WebResp.Server);
                Console.WriteLine("WebResp.ContentLength :- " + WebResp.ContentLength.ToString());
                Console.WriteLine(Environment.NewLine);
            }

item.BeginGetResponse
                    (
                       WriteResponseData, null
                    );

它给出了以下运行时错误：-

对象引用未设置为 对象的实例。在 WebRequestUsingAppm.Program.WriterResponseTA（IAsyncResult 结果）在 \webrequestusingaam\Program.cs:第73行 在 System.Net.LazyAsyncResult.Complete（IntPtr 用户令牌）在 System.Net.ContextawarerResult.CompleteCallback（对象 国家）在 System.Threading.ExecutionContext.Run（ExecutionContext executionContext，ContextCallback 回调，对象状态，布尔值 ignoreSyncCtx）在 System.Threading.ExecutionContext.Run（ExecutionContext executionContext，ContextCallback 回调，对象状态）在 System.Net.ContextAwareResult.Complete（IntPtr 用户令牌）在 System.Net.LazyAsyncResult.ProtectedInvokeCallback（对象 结果，IntPtr userToken）位于 System.Net.HttpWebRequest.ProcessResponse（）

编辑：-

---

我明白了。result.AsyncState返回null，因为我在调用BeginGetResponse（）时传递null，第二个参数是AsyncState，我在那里传递null。我应该在那里传递当前的WebRequest对象，这样就可以了

因此，与其说：-

WebRequest request = (WebRequest)result.AsyncState;
            if (result != null && result.IsCompleted)
            {
                HttpWebResponse WebResp = (HttpWebResponse)request.EndGetResponse(result);
                Console.WriteLine("WebResp.StatusCode :-" + WebResp.StatusCode);
                Console.WriteLine("WebResp.Server :- " + WebResp.Server);
                Console.WriteLine("WebResp.ContentLength :- " + WebResp.ContentLength.ToString());
                Console.WriteLine(Environment.NewLine);
            }

item.BeginGetResponse
                    (
                       WriteResponseData, null
                    );

我应该通过这个项目：-

item.BeginGetResponse
                        (
                           WriteResponseData, item
                        );

---

正如您所说，这段代码不会编译，因为WriteResponse方法不会引用item对象。调用begin request时，可以使用传递请求对象作为状态。请参阅MSDN

编辑：简化的代码模板将是

   item.BeginGetResponse(WriteResponseData, item);

并将writeResponda修改为

static void WriteResponseData(IAsyncResult result)
{
    WebRequest request = (WebRequest)result.AsyncState;
    WebResponse response = request.EndGetResponse(result);
    ....
}

---

我明白了。result.AsyncState返回null，因为我在调用BeginGetResponse（）时传递null，第二个参数是AsyncState，我在那里传递null。我应该在那里传递当前的WebRequest对象，这样就可以了。谢谢