StreamReader(response.GetResponseStream(), encoding)问题

Question

  response = (HttpWebResponse)request.GetResponse();                if (response.StatusCode == HttpStatusCode.OK && response.ContentLength < 1024 * 1024)
                {
                    if (encoding == null)
                    {
                        reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding("gbk"));
                        html = reader.ReadToEnd();
                        Match charSetMatch = Regex.Match(html, "<meta([^<]*)charset=([^<]*)\"", RegexOptions.IgnoreCase | RegexOptions.Multiline);
                        string webCharSet = charSetMatch.Groups[2].Value;
                        encoding = Encoding.GetEncoding(webCharSet);
                    }
                    reader = new StreamReader(response.GetResponseStream(), encoding);                     html = reader.ReadToEnd();
                    return html;
                }该部分代码为获取网页的编码方式，
经断点测试，红色部分错误求原因

Answer 1

写2遍reader = new StreamReader？

Answer 2

我也遇到这样的问题，有说streamread是只读向前的，难道response.GetResponseStream（）方法只能用一次？
问题解决了么？什么原因。。求解