지정한 URL 파일을 다운로드하거나 데이터 흐름과byte 그룹으로 변환하기

                   #region     
                    Stream stream = null;
                    string UrlImg = "https://mp.weixin.qq.com/cgi-bin/showqrcode?ticket=" + QRCode_WxHelper.CreateQRCode(QRmodel.QudaoId);
                    WebClient webClient = new WebClient();
                    webClient.Credentials = CredentialCache.DefaultCredentials;
                    //            
                    byte[] byteData = webClient.DownloadData(UrlImg); 
                    stream = BytesToStream(byteData);
                    string str64= System.Convert.ToBase64String(byteData);
                    #endregion 
        /// <summary>
        ///           
        /// </summary>
        /// <param name="bytes">     </param>
        /// <returns></returns>
        public Stream BytesToStream(byte[] bytes)
        {
            Stream stream = new MemoryStream(bytes);
            return stream;
        }
        /// <summary>
        ///           
        /// </summary>
        /// <param name="stream"></param>
        /// <returns></returns>
        public byte[] StreamToBytes(Stream stream)
        {
            byte[] bytes = new byte[stream.Length];
            stream.Read(bytes, 0, bytes.Length);
            //                 
            stream.Seek(0, SeekOrigin.Begin);
            return bytes;
        }