FormType.php

<?php
namespace Acme\WhateverBundle\FormType;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use Acme\WhateverBundle\FormSubscriber\UserListener;

class FriendMessageFormType extends AbstractType
{
    private $subscriber;

    public function __construct(UserListener $subscriber)
    {
        $this->subscriber = $subscriber;
    }

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('subject', 'text')
            ->add('body', 'textarea')
        ;
        $builder->addEventSubscriber($this->subscriber);
    }

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

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
    }
}