关于asp.net post提交数据的问题

[已关闭问题]

我想提交一段html代码到：http://validator.w3.org/#validate_by_input.然后获取他的验证结果

我用http watch看了下，post的格式为：

doctype    Inline
fragment    test html code
group    0
prefill    0
prefill_doctype    html401

我的代码如下：

string _validateSite = "http://validator.w3.org/check";
String _postStr = "doctype=Inline&fragment" + this.txb.Text+"&group=0&prefill=0&prefill_doctype=html401";
string _strResult = "";
            try
            {
                byte[] _byte = System.Text.Encoding.UTF8.GetBytes(_postData);
                HttpWebRequest _httpRequest = (HttpWebRequest)WebRequest.Create(_url);
                _httpRequest.ContentType = "application/x-www-form-urlencoded";
                _httpRequest.ContentLength = _byte.Length;
                _httpRequest.Method = "POST";
                Stream _postStream = _httpRequest.GetRequestStream();
                _postStream.Write(_byte, 0, _byte.Length);
                _postStream.Close();

                HttpWebResponse _response = (HttpWebResponse)_httpRequest.GetResponse();
                Stream _streamReceive = _response.GetResponseStream();
                Encoding _encoding = Encoding.GetEncoding("UTF-8");
                StreamReader _streamReader = new StreamReader(_streamReceive, _encoding);
                _strResult = _streamReader.ReadToEnd();

            }
            catch (Exception err)
            {
                _strResult = err.Message;
            }

            return _strResult;