点击下载浏览器会有下载的进度条所有不用，如果硬要的话可以做个加载页面下载完成就close掉

         /// 流式下载文件
         public static void DownLoadFile()
        {
            string fileName = "test.txt";//客户端保存的文件名

            string filePath = HttpContext.Current.Server.MapPath("../File/Temp/Parameter_Alias_Import_Template.xlsx");//路径 //以字符流的形式下载文件

            FileStream fs = new FileStream(filePath, FileMode.Open);

            byte[] bytes = new byte[(int)fs.Length]; fs.Read(bytes, 0, bytes.Length);

            fs.Close();

            HttpContext.Current.Response.ContentType = "application/octet-stream";

            HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));//通知浏览器下载文件而不是打开

            HttpContext.Current.Response.BinaryWrite(bytes);

            HttpContext.Current.Response.Flush();

            HttpContext.Current.Response.End();
        }