为什么request.UserAgent为空呢,如何解决.


        public string GetPageContent(string strurl)
        {
            try
            {
                string ResponseText = String.Empty;
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(strurl);
                request.UserAgent = HttpContext.Current.Request.UserAgent;
                WebResponse response = request.GetResponse();
                Stream resStream = response.GetResponseStream();
                StreamReader sr = new StreamReader(resStream, Encoding.UTF8);
                ResponseText = sr.ReadToEnd();
                resStream.Close();
                sr.Close();
                return ResponseText;
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }上面这段采集代码为什么放在Global文件中进行定时采集的时候都会报request.UserAgent 为空呢?