Download generated excel file with phpExcel as attachment when form is submitted in drupal 7 - drupal-7

Question

This is my code. Form submits, but no file is downloaded as attachment. No errors
function dn_preorder_form_submit($form,&$form_state){
$excel = new PHPExcel();
$excel->setActiveSheetIndex(0);
$excel->getActiveSheet()->setCellValue('A1',"TEST");
header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
header('Content-Disposition: attachment; filename="var.xlsx"');
header("Pragma: no-cache");
header("Cache-Control: no-cache");
header("Cache-Control: nmax-age=0");
$file = PHPExcel_IOFactory::createWriter($excel,'Excel2007');
$file->save('php://output');
}
I have tried this solution
https://drupal.stackexchange.com/questions/103690/download-file-on-form-submission
But i still get same results.
I have tried this code outside drupal and it works

Answer 1

OK, i solved it by inserting exit() at the end of the code
function dn_preorder_form_submit($form,&$form_state){
$excel = new PHPExcel();
$excel->setActiveSheetIndex(0);
$excel->getActiveSheet()->setCellValue('A1',"TEST");
header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
header('Content-Disposition: attachment; filename="var.xlsx"');
header("Pragma: no-cache");
header("Cache-Control: no-cache");
header("Cache-Control: nmax-age=0");
$file = PHPExcel_IOFactory::createWriter($excel,'Excel2007');
$file->save('php://output');
exit();
}