FormType.php

namespace Acme\DemoBundle\Form\Type;
<?php
use Symfony\Component\Form\AbstractType
use Symfony\Component\Form\FormBuilderInterface;
use Acme\DemoBundle\Form\EventListener\AddNameFieldSubscriber;

class ProductType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $subscriber = new AddNameFieldSubscriber($builder->getFormFactory());
        $builder->addEventSubscriber($subscriber);
        $builder->add('price');
    }

    public function getName()
    {
        return 'product';
    }
}