Winform下载文件

/// <summary>
        /// 下载文件
        /// </summary>
        /// <param name="URL">下载文件地址</param>
        /// <param name="Filename">下载后的存放地址</param>
        /// <param name="Prog">用于显示的进度条</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>
        /// 下载文件
        /// </summary>
        /// <param name="URL">下载文件地址</param>
        /// <param name="Filename">下载后的存放地址</param>
        public void DownloadFile(string URL, string filename)
        {
            DownloadFile(URL, filename, null);
        }