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;
  }
}

public class Example
{

  public static ManualResetEvent allDone= new ManualResetEvent(false);
  const int BUFFER_SIZE = 1024;

  public static void Demo(System.Windows.Controls.TextBlock outputBlock)
  {
  try
  {      

    System.Uri uri = new Uri("http://www.contoso.com");
    // Create a HttpWebrequest object to the desired URL.
    HttpWebRequest myHttpWebRequest1= (HttpWebRequest)WebRequest.Create(uri);

    // Create an instance of the RequestState and assign the previous myHttpWebRequest1
    // object to it's request field.  
    RequestState myRequestState = new RequestState();  
    myRequestState.request = myHttpWebRequest1;


    // Start the asynchronous request.
    IAsyncResult result=
      (IAsyncResult) myHttpWebRequest1.BeginGetResponse(new AsyncCallback(RespCallback),myRequestState);

  }
  catch(WebException e)
  {
    outputBlock.Text += "\nException raised!\n";
    outputBlock.Text += "Message: ";
    outputBlock.Text += e.Message;
    outputBlock.Text += "\nStatus: ";
    outputBlock.Text += e.Status;
    outputBlock.Text += "\n";
  }
  catch(Exception e)
  {
    outputBlock.Text += "\nException raised!\n";
    outputBlock.Text += "\nMessage: ";
    outputBlock.Text += e.Message;
    outputBlock.Text += "\n";
  }
}
private static void RespCallback(IAsyncResult asynchronousResult)
{  
  try
  {
    // State of request is asynchronous.
    RequestState myRequestState=(RequestState) asynchronousResult.AsyncState;
    HttpWebRequest  myHttpWebRequest2=myRequestState.request;
    myRequestState.response = (HttpWebResponse) myHttpWebRequest2.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);
  }
  catch(WebException e)
  {
    // Need to handle the exception
  }
}
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 do something with it
    if (read > 0)
    {
      myRequestState.requestData.Append(Encoding.UTF8.GetString(myRequestState.BufferRead, 0, read));
      IAsyncResult asynchronousResult = responseStream.BeginRead( myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
    }
    else
    {
      if(myRequestState.requestData.Length>1)
      {
        string stringContent;
        stringContent = myRequestState.requestData.ToString();
        // do something with the response stream here
      }

      responseStream.Close();
      allDone.Set();

    }

  }
  catch(WebException e)
  {
    // Need to handle the exception
  }

}