如何用c#编写文件

 string attachment = "attachment; filename=Myfile.csv";
 HttpContext.Current.Response.Clear();
 HttpContext.Current.Response.ClearHeaders();
 HttpContext.Current.Response.ClearContent();
 HttpContext.Current.Response.AddHeader("content-disposition", attachment);
 HttpContext.Current.Response.ContentType = "text/csv";
 HttpContext.Current.Response.AddHeader("Pragma", "public");
// My logic goes here to write file.
// Now I want to copy above file to another file.
 string filepath = Server.MapPath("~/ExportedFiles/") +"Newfile.csv";
 var ExcelFile = File.Create(filepath);
 ExcelFile.Close();
 HttpContext.Current.Response.TransmitFile(filepath);
 HttpContext.Current.Response.Flush();

以上代码不工作，请建议我。谢谢。