Here is a simple code snippet for creating an xlsx file and opening it with OpenOffice:
require(APPPATH.'/PHPExcel-1.8/Classes/PHPExcel.php');
require(APPPATH.'/PHPExcel-1.8/Classes/PHPExcel/Writer/Excel2007.php');
$this->load->library('excel');
$objPHPExcel = new PHPExcel();
$objPHPExcel->setActiveSheetIndex(0)
->SetCellValue('A1', 'Calendario Attivit');
$filename = "prova".".xlsx";
header("Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
header('Content-Disposition: attachment;filename="'.$filename.'"');
header("Cache-Control: max-age=0");
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
$objWriter->save('php://output');
exit;
After downloading the file and attempting to open it, I encountered this issue:
https://i.stack.imgur.com/MnVlz.png
If anyone has suggestions on how to resolve this problem, please let me know!