C# WinForm下載檔案

        /// <summary>        /// 下載檔案(顯示進度)        /// </summary>        /// <param name="URL"></param>        /// <param name="filename"></param>        /// <param name="prog"></param>        public void DownloadFile(string URL, string filename, System.Windows.Forms.ProgressBar prog)        {            try            {                System.Net.HttpWebRequest Myrq = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(URL);                System.Net.HttpWebResponse myrp = (System.Net.HttpWebResponse)Myrq.GetResponse();                long totalBytes = myrp.ContentLength;                if (prog != null)                {                    prog.Maximum = (int)totalBytes;                }                System.IO.Stream st = myrp.GetResponseStream();                System.IO.Stream so = new System.IO.FileStream(filename, System.IO.FileMode.Create);                long totalDownloadedByte = 0;                byte[] by = new byte[1024];                int osize = st.Read(by, 0, (int)by.Length);                while (osize > 0)                {                    totalDownloadedByte = osize + totalDownloadedByte;                    System.Windows.Forms.Application.DoEvents();                    so.Write(by, 0, osize);                    if (prog != null)                    {                        prog.Value = (int)totalDownloadedByte;                    }                    osize = st.Read(by, 0, (int)by.Length);                }                so.Close();                st.Close();            }            catch (System.Exception)            {                throw;            }        }        /// <summary>        /// 下載檔案        /// </summary>        /// <param name="URL"></param>        /// <param name="filename"></param>        public void DownloadFile(string URL, string filename)        {            DownloadFile(URL,filename,null);        }