Detect File Download Completion

worksheet.Tables[0].ShowFilter = true;

                HttpContext.Current.Response.ClearHeaders();
                HttpContext.Current.Response.ClearContent();
                HttpContext.Current.Response.Clear();
               // HttpContext.Current.Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
                HttpContext.Current.Response.ContentType = "application/x-msexcel";
                HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;filename=" + strfileName + ".xlsx");
                HttpContext.Current.Response.AddHeader("Content-Length", package.GetAsByteArray().Length.ToString());
                //HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.GetEncoding("utf-8");
                HttpContext.Current.Response.ContentEncoding = System.Text.UTF8Encoding.UTF8;
                if (HttpContext.Current.Response.IsClientConnected)
                {
                    HttpContext.Current.Response.BinaryWrite(package.GetAsByteArray());
                }
                HttpContext.Current.Response.Flush();
                HttpContext.Current.Response.Close();