embedding current user id in a form Symfony 2 - php

Question

I am trying to validate a form in Symfony 2.3. I need to get the current User id and submit in my database.
My controller :
public function giftcardAction(Request $request)
{
$giftcard = new Giftcard();
$giftcard->setDate(new \DateTime());
$user = $this->container->get('security.context')->getToken()->getUser();
$userId = $user->getId();
var_dump($userId);
$form = $this->createFormBuilder($giftcard)
->add('amount', 'integer')
->add('onBehalfOf')
->add('towards')
->add('message', 'text')
// ->add($userId)
->add('submit', 'submit')
->getForm();
$form->handleRequest($request);
if ($form->isValid()) {
$em = $this->getDoctrine()->getManager();
$em->persist($giftcard);
$em->flush();
}else{
throw new NotFoundHttpException("Page not found");
}
}
return $this->render('FrontBundle:Forms:giftcard.html.twig', array(
'form' => $form->createView(),
));
}
My FormType
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
class GiftCardType extends AbstractType
{
private $userId;
public function __construct(array $userId)
{
$this->userId = $userId;
}
/**
* #param FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('date')
->add('onBehalfOf')
->add('towards')
->add('message')
// ->add('UserId')
;
}
/**
* #param OptionsResolverInterface $resolver
*/
public function setDefaultOptions(OptionsResolverInterface $resolver)
{
$resolver->setDefaults(array(
'data_class' => 'Front\Bundle\Entity\GiftCard',
));
}
/**
* #return string
*/
public function getName()
{
return 'front_bundle_giftcard';
}
}
At the moment i can get the user id in var_dump in the controller. But how I can pass the variable in the form. Has anyone may help me. Thank you.