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;
        }