Yii2: refresh() not working after sending response content - yii2

Question

I have a ActiveForm which I use to get some data from and when I click the send button it will run the model (in this case a csv file generator) but the refresh is not working, when I remove the method it will refresh.
After some testing it seems that fputcsv() will stop the script, so that everything that comes after this will not run.
view
public function actionIndex()
{
$model = new Export();
if ($model->load(Yii::$app->request->post()) && $model->validate()) {
$fields = Yii::$app->request->post('Export');
\backend\models\Export::generate();//this prevents the refresh
Yii::$app->session->setFlash();
return $this->refresh();
} else {
return $this->render('index' , ['model' => $model]);
}
}
model
static public function generate()
{
header('Content-Encoding: UTF-8');
header('Content-Type: text/csv; charset=UTF-8');
header('Content-Disposition: attachment; filename="sample.csv"');
header("Pragma: no-cache");
header("Expires: 0");
$data = [array comes here];
$fp = fopen('php://output', 'w') or die("Unable to open file!");
fputs($fp, $bom =( chr(0xEF) . chr(0xBB) . chr(0xBF) ));
foreach ( $data as $line ) {
fputcsv($fp , $line , ';' );
}
stream_get_contents($fp);
fclose($fp);
}

Answer 1

Controller::refresh() uses Location header to reload page. Since headers need to precede the content, you cannot add new header after content was sent. Your Export::generate() method sends content, so you cannot add any header after that, thus $this->refresh() do not work.
Prior to Yii 2.0.14 there was a bug and framework simply ignored that you're trying to send header after content has been send. If you upgrade Yii, you should get "nice" Exception in this case.
If you're trying to display nice page after downloading file, your approach is incorrect. You can't really return file and then redirect to different page. You should first display nice HTML page and inside of it redirect user to download page (for example by using <meta http-equiv="refresh" content="0; url=http://example.com/" /> in head or creating hidden form and submitting it by JavaScript). After downloading the file user will stay at this nice page, so from UX perspective everything should be OK.