我无法交换文件。 从XLS到XLSX

Question

I'm trying to make a change in the application code, because I've tried it anyway and I'm not having success. I have a reporting tab on my system, but it is only exporting XLS files and I need to switch to XLSX because the XLS is limited to 65,000 lines. I'll show a part of my controler when he's mounting the XLS. I can not show my Service method because it is VERY large and you would be kind of lost.

[CustomAuthorize(TipoFuncao.PRINT)]
public ActionResult Index(FiltroRptManifesto filtro)
{
    byte[] result = null;
    bool overflowMonth = false;
    IWorkbook workbook = new XSSFWorkbook();

    try
    {                
        RptManifestoService rptManifestoService = new RptManifestoService(ModelState);
        result = rptManifestoService.GeraExcel(Server.MapPath("~/Content/RptManifesto.xls"), filtro, ViewBag.Usuario);
        if (ModelState.IsValid)
        {
             if (ValidateDate(ModelState["DtProtocoloIni"].Value, ModelState["DtProtocoloFin"].Value).Days > 540)
             {
                 overflowMonth = true;
                 throw new Exception();
             };

             Response.AppendCookie(new HttpCookie("downloadToken", filtro.DownloadToken));                                    
             return File(result, "application/vnd.ms-excel", "Manifesto.xls");
        }
    }
//...

Answer 1

I've never used NPOI so I may be wrong but what happens if you do:

var fileName = "Manifesto.xlsx";
return File(result, MimeMapping.GetMimeMapping(fileName), fileName);

or

return File(
        result, 
        "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", 
        "Manifesto.xlsx");