this is because you cant store files in the session...
here a possibility to manage it..
Controller
// ...
if ($flow->isValid($form)) {
$data = $request->request->get($form->getName(), array());
// upload the entity (Event) main picture
if ($event->preUpload() && $picture = $event->upload()) {
$data['picture'] = $picture;
}
// save form progress
$flow->saveCurrentStepData($data);
// ...
Entity Event
// ...
public function preUpload()
{
if(null !== $this->picturefile)
{
$this->picture = uniqid() . '.' . $this->picturefile->guessExtension();
return $this->picture;
}
}
And you have to overwrite the FormFlow method saveCurrentStepData() ... (with a custom Bundle with getParent)
public function saveCurrentStepData($data = false) {
$sessionData = $this->getSessionData();
$sessionData[$this->currentStep] = $data ? $data : $this->request->request->get($this->formType->getName(), array()) ;
$this->setSessionData($sessionData);
}