下载大型EXCEL文件

Question

我使用的是WINDOWS 7，IIS 7 Express 我想从服务器下载excel .xlsx文件（2013）。它可以下载但不能打开。使用xls时同样的问题。我错过了什么？ 这是代码：

   public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "text/plain";


        string mediaName = HttpContext.Current.Request.QueryString["n"].ToString();
        if (string.IsNullOrEmpty(mediaName))
        {
            return;
        }
        string destPath = context.Server.MapPath("~/EXCELtemplates/" + mediaName);
        // Check to see if file exist
        FileInfo fi = new FileInfo(destPath);

        try
        {
            if (fi.Exists)
            {
                HttpContext.Current.Response.ClearHeaders();
                HttpContext.Current.Response.ClearContent();
                HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment; filename=" + fi.Name);
                HttpContext.Current.Response.AppendHeader("Content-Length", fi.Length.ToString());
              //HttpContext.Current.Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";   // (xlsx)
                HttpContext.Current.Response.ContentType = "application/vnd.ms-excel";
                HttpContext.Current.Response.TransmitFile(fi.FullName);
                HttpContext.Current.Response.Flush();
            }
        }
        catch (Exception exception)
        {
            HttpContext.Current.Response.ContentType = "text/plain";
            HttpContext.Current.Response.Write(exception.Message);
        }
        finally
        {
            HttpContext.Current.Response.End();
        }
    }