C#的HttpWebRequest编程，支持带ViewState的网页POST请求

从网上找到了Jake Lin（Jake's Blog on 博客园）的一篇文章《.NET Compact Framework下HttpWebRequest开发》，在他的代码基础上稍加修改，可以编程模拟网页POST提交的效果。

在主程序上用了个循环，再将取出的网页用正则表达式把想要的信息取出来，最后成功地提取出了石油大学附中2010小升初的成绩表。

static private string SearchURL(string id)
{
try
{
    //Get the ViewState and EventValidation
    HttpWebRequest request = WebRequest.Create(URI) as HttpWebRequest;
    request.Method ="GET";
    request.KeepAlive =false;

    //Get the response
    HttpWebResponse response = request.GetResponse() as HttpWebResponse;
    System.IO.Stream responseStream = response.GetResponseStream();
    System.IO.StreamReader reader =new System.IO.StreamReader(responseStream, Encoding.UTF8);
    string srcString = reader.ReadToEnd();

    //Get the ViewState
    string viewStateFlag ="id=\"__VIEWSTATE\" value=\"";
    int i = srcString.IndexOf(viewStateFlag) + viewStateFlag.Length;
    int j = srcString.IndexOf("\"", i);
    string viewState = srcString.Substring(i, j - i);

    //Get the ViewState
    string EventValidationFlag ="id=\"__EVENTVALIDATION\" value=\"";
    i = srcString.IndexOf(EventValidationFlag) + EventValidationFlag.Length;
    j = srcString.IndexOf("\"", i);
    string eventValidation = srcString.Substring(i, j - i);

    //Compose the URL
    viewState = Uri.EscapeDataString(viewState);
    eventValidation = Uri.EscapeDataString(eventValidation);
    string strSearch = Uri.EscapeDataString("查询");

    string formatString ="__VIEWSTATE={0}&__EVENTVALIDATION={1}&TextBox1={2}&Button1={3}";
    string postString =string.Format(formatString, viewState, eventValidation, id,strSearch);

    //Change to byte[]
    byte[] postData = Encoding.ASCII.GetBytes(postString);

    //Compose the new request
    request = WebRequest.Create(URI) as HttpWebRequest;
    request.Method ="POST";
    request.KeepAlive =false;
    request.ContentType ="application/x-www-form-urlencoded";
    request.ContentLength = postData.Length;

    System.IO.Stream outputStream = request.GetRequestStream();
    outputStream.Write(postData, 0, postData.Length);
    outputStream.Close();

    //Get the new response
    response = request.GetResponse() as HttpWebResponse;
    responseStream = response.GetResponseStream();
    reader =new System.IO.StreamReader(responseStream);
    srcString = reader.ReadToEnd();
    return srcString;
}
catch (WebException we)
{
    Console.WriteLine("Communication error,"+ we.Message +" please check your connectivity and try again.", "Error");
}
catch
{
    Console.WriteLine("Unknow error.", "Error");
}
return null;
}