C＃屏幕抓取处理登录控件

Question

我正在尝试使用屏幕抓取登录网站，我遇到了困难。

    HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(uri);
    req.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; WOW64; SLCC1; .NET CLR 2.0.50727; .NET CLR 3.0.30729; .NET CLR 3.5.30729; InfoPath.2; .NET4.0C; .NET4.0E; MS-RTC LM 8)";
    req.KeepAlive = false;
    req.Proxy = new WebProxy(IPAddress,PORT);
    req.Method = "POST";
    req.Host = host;
    req.Referer = referer;
    req.ContentType = "application/x-www-form-urlencoded";
    req.ContentLength = postBytes.Length;

    StreamWriter requestwriter = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);
    requestwriter.Write(postData);
    requestwriter.Close();

    try
    {
        using (HttpWebResponse res = (HttpWebResponse)req.GetResponse())
        {
            using (StreamReader sr = new StreamReader(res.GetResponseStream()))
            {
                sid = sr.ReadToEnd().Trim();
            }
        }
    }
    catch (WebException e)
    {
        Console.WriteLine(uri.ToString());
        Console.WriteLine(e.Message);
    }

    return sid;
}

我得到的所有内容都是登录表单，它永远不会登录我。任何想法？之前有人问过，有人可以帮我解决这个问题......我遇到了同样的问题