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 ;
}