c# wince5.0或6.0系统开发netCf3.5环境里居然没有 System.Net.WebClient类,所以找不到DownloadFile方法

        private bool DownFile()
        {
            string file_url = 资源网址
            string fn = 本地文件名;
          
            FileStream fs = new FileStream(fn, FileMode.Create);
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(file_url);
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            Stream stream = response.GetResponseStream();

            int bufferSize = 2048;
            byte[] bytes = new byte[bufferSize];

            try
            {
                int length = stream.Read(bytes, 0, bufferSize);

                while (length > 0)
                {
                    fs.Write(bytes, 0, length);
                    length = stream.Read(bytes, 0, bufferSize);
                }
                stream.Close();
                fs.Close();
                response.Close();
                return true;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
                return false;
            }
        }