EventListener mit PRE_SET_DATA-Event in Symfony2

sf2tt_001.php

/* ... */
public function buildForm(FormBuilder $builder, array $options)
{
    $builder->addEventListener(FormEvents::PRE_SET_DATA,
        function (DataEvent $event) use ($builder)
    {
        $form = $event->getForm();
        /* @var \Sperrobjekt\Sf2ttBundle\Entity\Category $data */
        $data = $event->getData();

        if ($data instanceof \Sperrobjekt\Sf2ttBundle\Entity\Category) {
            $label = $data->getName();
            $form->add($builder->getFormFactory()->createNamed(
                'text',
                'Category Name',
                null,
                array(
                    'label' => $label,
                )
            ));
        }
    });
}
/* ... */