一段代码部分看不明白,问一下大家什么意思?

[dabobonimama]

　　using System;
using System.Net;
using System.IO;
using System.Text;
using System.Threading;


public class RequestState
{
  // This class stores the State of the request.
  const int BUFFER_SIZE = 1024;
  public StringBuilder requestData;
  public byte[] BufferRead;
  public HttpWebRequest request;
  public HttpWebResponse response;
  public Stream streamResponse;
  public RequestState()
  {
    BufferRead = new byte[BUFFER_SIZE];
    requestData = new StringBuilder("");
    request = null;
    streamResponse = null;
  }
}

class HttpWebRequest_BeginGetResponse
{
  public static ManualResetEvent allDone= new ManualResetEvent(false);
  const int BUFFER_SIZE = 1024;
  const int DefaultTimeout = 2 * 60 * 1000; // 2 minutes timeout

  // Abort the request if the timer fires.
  private static void TimeoutCallback(object state, bool timedOut) { 
      if (timedOut) {
          HttpWebRequest request = state as HttpWebRequest;
          if (request != null) {
              request.Abort();
          }
      }
  }

  static void Main()
  {  

    try
    {
      // Create a HttpWebrequest object to the desired URL. 
      HttpWebRequest myHttpWebRequest= (HttpWebRequest)WebRequest.Create("http://www.contoso.com");


  /**
    * If you are behind a firewall and you do not have your browser proxy setup
    * you need to use the following proxy creation code.

      // Create a proxy object.
      WebProxy myProxy = new WebProxy();

      // Associate a new Uri object to the _wProxy object, using the proxy address
      // selected by the user.
      myProxy.Address = new Uri("http://myproxy");


      // Finally, initialize the Web request object proxy property with the _wProxy
      // object.
      myHttpWebRequest.Proxy=myProxy;
    ***/

      // Create an instance of the RequestState and assign the previous myHttpWebRequest
      // object to its request field.  
      RequestState myRequestState = new RequestState();  
      myRequestState.request = myHttpWebRequest;


      // Start the asynchronous request.
      IAsyncResult result=
        (IAsyncResult) myHttpWebRequest.BeginGetResponse(new AsyncCallback(RespCallback),myRequestState);

      // this line implements the timeout, if there is a timeout, the callback fires and the request becomes aborted
      ThreadPool.RegisterWaitForSingleObject (result.AsyncWaitHandle, new WaitOrTimerCallback(TimeoutCallback), myHttpWebRequest, DefaultTimeout, true);

      // The response came in the allowed time. The work processing will happen in the 
      // callback function.
      allDone.WaitOne();

      // Release the HttpWebResponse resource.
      myRequestState.response.Close();
    }
    catch(WebException e)
    {
      Console.WriteLine("\nMain Exception raised!");
      Console.WriteLine("\nMessage:{0}",e.Message);
      Console.WriteLine("\nStatus:{0}",e.Status);
      Console.WriteLine("Press any key to continue..........");
    }
    catch(Exception e)
    {
      Console.WriteLine("\nMain Exception raised!");
      Console.WriteLine("Source :{0} " , e.Source);
      Console.WriteLine("Message :{0} " , e.Message);
      Console.WriteLine("Press any key to continue..........");
      Console.Read();
    }
  }
  private static void RespCallback(IAsyncResult asynchronousResult)
  {  
    try
    {
      // State of request is asynchronous.
      RequestState myRequestState=(RequestState) asynchronousResult.AsyncState;
      HttpWebRequest  myHttpWebRequest=myRequestState.request;
      myRequestState.response = (HttpWebResponse) myHttpWebRequest.EndGetResponse(asynchronousResult);

      // Read the response into a Stream object.
      Stream responseStream = myRequestState.response.GetResponseStream();
      myRequestState.streamResponse=responseStream;

      // Begin the Reading of the contents of the HTML page and print it to the console.
      IAsyncResult asynchronousInputRead = responseStream.BeginRead(myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
      return;
    }
    catch(WebException e)
    {
      Console.WriteLine("\nRespCallback Exception raised!");
      Console.WriteLine("\nMessage:{0}",e.Message);
      Console.WriteLine("\nStatus:{0}",e.Status);
    }
    allDone.Set();
  }
  private static  void ReadCallBack(IAsyncResult asyncResult)
  {
    try
    {

    RequestState myRequestState = (RequestState)asyncResult.AsyncState;
    Stream responseStream = myRequestState.streamResponse;
    int read = responseStream.EndRead( asyncResult );
    // Read the HTML page and then print it to the console.
    if (read > 0)
    {
      myRequestState.requestData.Append(Encoding.ASCII.GetString(myRequestState.BufferRead, 0, read));
      IAsyncResult asynchronousResult = responseStream.BeginRead( myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
      return;
    }
    else
    {
      Console.WriteLine("\nThe contents of the Html page are : ");
      if(myRequestState.requestData.Length>1)
      {
        string stringContent;
        stringContent = myRequestState.requestData.ToString();
        Console.WriteLine(stringContent);
      }
      Console.WriteLine("Press any key to continue..........");
      Console.ReadLine();

      responseStream.Close();
    }

    }
    catch(WebException e)
    {
      Console.WriteLine("\nReadCallBack Exception raised!");
      Console.WriteLine("\nMessage:{0}",e.Message);
      Console.WriteLine("\nStatus:{0}",e.Status);
    }
    allDone.Set();

  }

这句代码IAsyncResult result=
(IAsyncResult) myHttpWebRequest.BeginGetResponse(new AsyncCallback(RespCallback),myRequestState);
我们知道调用了RespCallback这个函数.
现在我想问一下这个函数的传入参数是什么呀?即private static void ReadCallBack(IAsyncResult asyncResult)
中的asyncResult这个实际传入参数是什么?是上面的myRequestState吗??

不太理解望高手指点下,谢谢!!

[fengjian_428]

ReadCallBack的参数是myRequestState没错

[dabobonimama]

[Quote=引用 1 楼 fengjian_428 的回复:]
ReadCallBack的参数是myRequestState没错
[/Quote]
怎么理解的?是BeginGetResponse函数有这样一个功能?第２个参数传递给第一个参数了?

[Jack2013tong]

对

[fengjian_428]

AsyncCallback是一个带IAsyncResult参数的委托 new AsyncCallback(RespCallback)使委托对应到RespCallback方法。给委托传参就在后面写，实际就是给RespCallback方法传参了

[dabobonimama]

还是AsyncCallback委托具有这样的功能?

[dabobonimama]

[Quote=引用 4 楼 fengjian_428 的回复:]
AsyncCallback是一个带IAsyncResult参数的委托 new AsyncCallback(RespCallback)使委托对应到RespCallback方法。给委托传参就在后面写，实际就是给RespCallback方法传参了
[/Quote]
哦,那么是不是可以这样理解.
当一个方法需要用AsyncCallback当作参数时候,如需要给new AsyncCallback(RespCallback)对应方法传参数,那么需要再另外添加一个参数.

感觉AsyncCallback这个委托好神奇呀这样

[dabobonimama]

为什么不设计成IAsyncResult result=
(IAsyncResult) myHttpWebRequest.BeginGetResponse(new AsyncCallback(RespCallback(myRequestState));
这样呢?不是更好理解吗

[fengjian_428]

[Quote=引用 2 楼 dabobonimama 的回复:]
引用 1 楼 fengjian_428 的回复:
ReadCallBack的参数是myRequestState没错

怎么理解的?是BeginGetResponse函数有这样一个功能?第２个参数传递给第一个参数了?
[/Quote]
是啊 他就是这样定义的 线程池不也是这样吗

[fengjian_428]

委托是一个封装的函数指针 只能与函数直接关联 而函数的参数要额外传
可能是因为这个原因吧

用习惯了之后就不觉得怪了。

[dabobonimama]

哦,我理解下先,看样子我是对委托还没完全理解
我只是对+= new EventHandler()这样知道了，即先定义委托,然后给事件关联,最后调用事件即触发委托.
对上面这种情况还不是太了解呢

[dabobonimama]

上面这个是不是走到IAsyncResult result=
(IAsyncResult) myHttpWebRequest.BeginGetResponse(new AsyncCallback(RespCallback),myRequestState);
这句就立刻执行了RespCallback函数呢,应为这里好像没有事件订阅的概念呢

[fengjian_428]

什么时候执行是BeginGetResponse的事 你只是传了个委托给它

[dabobonimama]

[Quote=引用 12 楼 fengjian_428 的回复:]
什么时候执行是BeginGetResponse的事 你只是传了个委托给它
[/Quote]

你的意思这里不立刻执行,还要事件去触发??

[风骑士之怒]

up

[fwacky]

有点深度！

[cena_jin]

吼吼！！！

[fengjian_428]

[Quote=引用 13 楼 dabobonimama 的回复:]
引用 12 楼 fengjian_428 的回复:
什么时候执行是BeginGetResponse的事 你只是传了个委托给它


你的意思这里不立刻执行,还要事件去触发??
[/Quote]
BeginGetResponse获得了你给它的函数指针 然后在自己内部去调用 至于什么时候调用是它的事