Symfony2窗体-嵌入窗体和事件侦听器

我有一个带有事件侦听器的窗体"AddressType"，当单独实例化时，它可以按预期工作。这是代码。

namespace Nc'ClientsBundle'Form;
use Symfony'Component'Form'AbstractType;
use Symfony'Component'Form'FormBuilder;
use Nc'ClientsBundle'Form'EventListener'AddCityFieldSubscriber;
class AddressType extends AbstractType
{
    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder
            ->add('street')
            ->add('number', 'text')
            ->add('complement')
            ->add('district')
            ->add('state', 'entity', array(
                'class' => 'ClientsBundle:State', 
                'property' => 'name',
            ));
        $subscriber = new AddCityFieldSubscriber($builder->getFormFactory());
        $builder->addEventSubscriber($subscriber);
    }
    public function getDefaultOptions(array $options)
    {
        return array(
            'data_class' => 'Nc'ClientsBundle'Entity'Address',
        );
    }
    public function getName()
    {
        return 'addresstype';
    }
}

<?php
namespace Nc'ClientsBundle'Form'EventListener;
use Symfony'Component'Form'Event'DataEvent;
use Symfony'Component'Form'FormFactoryInterface;
use Symfony'Component'EventDispatcher'EventSubscriberInterface;
use Symfony'Component'Form'FormEvents;
use Doctrine'ORM'EntityRepository;
class AddCityFieldSubscriber implements EventSubscriberInterface
{
    private $factory;
    public function __construct(FormFactoryInterface $factory)
    {
        $this->factory = $factory;
    }
    public static function getSubscribedEvents()
    {
        // Tells the dispatcher that we want to listen on the form.pre_set_data
        // event and that the preSetData method should be called.
        return array(FormEvents::PRE_SET_DATA  => 'preSetData');
    }
    public function preSetData(DataEvent $event)
    {
        $data = $event->getData();
        $form = $event->getForm();
        // During form creation setData() is called with null as an argument
        // by the FormBuilder constructor. We're only concerned with when
        // setData is called with an actual Entity object in it (whether new,
        // or fetched with Doctrine). This if statement let's us skip right
        // over the null condition.
        if (null === $data) {
            return;
        }
        if (!$data->getCity()) {
            $form->add($this->factory->createNamed('city_selector', 'city', null, array(
                'choices'   => array('' => '--  Selecione um estado  --'),
                'required'  => true,
                'expanded'  => false,
                'multiple'  => false,
            )));
        } else {
            $city = $data->getCity();
            $form->add($this->factory->createNamed('city_selector', 'city', null, array(
                'choices'   => array($city->getId() => $city->getName()),
                'required'  => true,
                'expanded'  => false,
                'multiple'  => false,
            )));
        }
    }
}
<?php
namespace Nc'ClientsBundle'Form'Type;
use Symfony'Component'Form'AbstractType;
use Symfony'Component'Form'FormBuilder;
use Symfony'Component'OptionsResolver'OptionsResolverInterface;
use Doctrine'Common'Persistence'ObjectManager;
use Nc'ClientsBundle'Form'DataTransformer'CityToIdTransformer;
class CitySelectorType extends AbstractType
{
    /**
     * @var ObjectManager
     */
    private $om;
    /**
     * @param ObjectManager $om
     */
    public function __construct(ObjectManager $om)
    {
        $this->om = $om;
    }
    public function buildForm(FormBuilder $builder, array $options)
    {
        $transformer = new CityToIdTransformer($this->om);
        $builder->prependNormTransformer($transformer);
    }
    public function getDefaultOptions(array $options)
    {
        return array(
            'invalid_message' => 'Selecione um estado e uma cidade.',
        );
    }
    public function getParent(array $options)
    {
        return 'choice';
    }
    public function getName()
    {
        return 'city_selector';
    }
}
<?php
namespace Nc'ClientsBundle'Form'DataTransformer;
use Symfony'Component'Form'DataTransformerInterface;
use Symfony'Component'Form'Exception'TransformationFailedException;
use Doctrine'Common'Persistence'ObjectManager;
use Nc'ClientsBundle'Entity'City;
class CityToIdTransformer implements DataTransformerInterface
{
    /**
     * @var ObjectManager
     */
    private $om;
    /**
     * @param ObjectManager $om
     */
    public function __construct(ObjectManager $om)
    {
        $this->om = $om;
    }
    /**
     * Transforms an object (city) to a integer (id).
     *
     * @param  City|null $city
     * @return string
     */
    public function transform($city)
    {
        if ($city === null) {
            return '';
        }
        return $city->getId();
    }
    /**
     * Transforms a string (id) to an object (city).
     *
     * @param  string $id
     * @return City|null
     * @throws TransformationFailedException if object (city) is not found.
     */
    public function reverseTransform($id)
    {
        if (!$id) {
            return null;
        }
        $city = $this->om
            ->getRepository('ClientsBundle:City')
            ->findOneBy(array('id' => $id))
        ;
        if (null === $city) {
            throw new TransformationFailedException(sprintf(
                'An city with id "%s" does not exist!',
                $id
            ));
        }
        return $city;
    }
}

结果是，当我试图将此表单嵌入到"ClientType"表单中时，"city"字段不会被呈现。

namespace Nc'ClientsBundle'Form;
use Symfony'Component'Form'AbstractType;
use Symfony'Component'Form'FormBuilder;
class ClientType extends AbstractType
{
    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder->add('name');
        $builder->add('type', 'choice', array(
            'choices'   => array('1' => 'Comum', '2' => 'Parceiro'),
            'expanded'  => true,
            'multiple'  => false,
            'required'  => true,
        ));
        $builder->add('contactInfo', new ContactInfoType(), array('label' => ' '));
        $builder->add('address', new AddressType(), array('label' => ' '));
    }
    public function getDefaultOptions(array $options)
    {
        return array(
            'data_class' => 'Nc'ClientsBundle'Entity'Client',
        );
    }
    public function getName()
    {
        return 'clienttype';
    }
}