CookieContainer cookieContainer = new CookieContainer();

        ///////////////////////////////////////////////////
        // 1.打开 MyLogin.aspx 页面，获得 GetVeiwState & EventValidation
        ///////////////////////////////////////////////////                
        // 设置打开页面的参数   
        string URI = "http://passport.cnblogs.com/login.aspx";
        HttpWebRequest request = WebRequest.Create(URI) as HttpWebRequest;
        request.Method = "GET";
        request.KeepAlive = false;

        // 接收返回的页面
        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();

        // 获取页面的 VeiwState                
        string viewStateFlag = "id=\"__VIEWSTATE\" value=\"";
        int i = srcString.IndexOf(viewStateFlag) + viewStateFlag.Length;
        int j = srcString.IndexOf("\"", i);
        string viewState = srcString.Substring(i, j - i);

        // 获取页面的 EventValidation                
        string eventValidationFlag = "id=\"__EVENTVALIDATION\" value=\"";
        i = srcString.IndexOf(eventValidationFlag) + eventValidationFlag.Length;
        j = srcString.IndexOf("\"", i);
        string eventValidation = srcString.Substring(i, j - i);


        ///////////////////////////////////////////////////
        // 2.自动填充并提交 MyLogin.aspx 页面
        ///////////////////////////////////////////////////
        // 提交按钮的文本
        string submitButton = "登  录";

        // 用户名和密码
        string userName = "11";
        string password = "22";

        // 将文本转换成 URL 编码字符串
        viewState = System.Web.HttpUtility.UrlEncode(viewState);
        eventValidation = System.Web.HttpUtility.UrlEncode(eventValidation);
        submitButton = System.Web.HttpUtility.UrlEncode(submitButton);

        // 要提交的字符串数据。格式形如:user=uesr1&password=123
        string formatString = "tbUserName={0}&tbPassword={1}&btnLogin={2}&__VIEWSTATE={3}&__EVENTVALIDATION={4}";
        string postString = string.Format(formatString, userName, password, submitButton, viewState, eventValidation);

        // 将提交的字符串数据转换成字节数组
        byte[] postData = Encoding.ASCII.GetBytes(postString);

        // 设置提交的相关参数
        request = WebRequest.Create(URI) as HttpWebRequest;
        request.Method = "POST";
        request.KeepAlive = false;
        request.ContentType = "application/x-www-form-urlencoded";
        request.CookieContainer = cookieContainer;
        request.ContentLength = postData.Length;

        // 提交请求数据
        System.IO.Stream outputStream = request.GetRequestStream();
        outputStream.Write(postData, 0, postData.Length);
        outputStream.Close();

        // 接收返回的页面
        response = request.GetResponse() as HttpWebResponse;
        responseStream = response.GetResponseStream();
        reader = new System.IO.StreamReader(responseStream, Encoding.UTF8);
        srcString = reader.ReadToEnd();

        ///////////////////////////////////////////////////
        // 3.打开 Default.aspx 页面
        ///////////////////////////////////////////////////
        // 设置打开页面的参数
        URI = "http://passport.cnblogs.com/login.aspx";
        request = WebRequest.Create(URI) as HttpWebRequest;
        request.Method = "GET";
        request.KeepAlive = false;
        request.CookieContainer = cookieContainer;

        // 接收返回的页面
        response = request.GetResponse() as HttpWebResponse;
        responseStream = response.GetResponseStream();
        reader = new System.IO.StreamReader(responseStream, Encoding.UTF8);
        srcString = reader.ReadToEnd();