$id = $this->get('request')->get($this->admin->getIdParameter());

    $object = $this->admin->getObject($id);

    if (!$object) {
        throw new NotFoundHttpException(sprintf('unable to find the object with id : %s', $id));
    }

    if (false === $this->admin->isGranted('EDIT', $object)) {
        throw new AccessDeniedException();
    }

    // On vérifie que l'annonce appartient bien à l'utilisateur connecté
    if($this->getUser()->getId() !== $object->getUser()->getId()) {
        throw new AccessDeniedException();
    }

    $em = $this->getDoctrine()->getManager();
    $preparechoices = $em->getRepository('AcmeBundle:Entity')->findAll();

    foreach($preparechoices as $c){
        $choices[$c->getId()] = $c->getLibelle();
    }


    $form = $this->createFormBuilder(array('choix'=>1))
        ->add('choix','choice',array('choices'=>$choices))
        ->add('submit','submit')
        ->getForm();

    $view = $form->createView();


    $this->admin->setSubject($object);
    $this->get('twig')->getExtension('form')->renderer->setTheme($view, $this->admin->getFormTheme());
    return $this->render($this->admin->getTemplate('EDIT'), array(
        'action'   => 'edit',
        'object'   => $object,
        'form'     => $view,
    ));
}

Impossible to access a key ("default") on a boolean variable ("")

{{ form_helper.render_groups(admin, form, admin.formtabs['default'].groups, has_tab) }}