Add event listener to form element added by event listener

If anybody else has a similar issue, I eventually got it right with event subscribers for each field, with help from this site (translate it for those non-spanish speaking folk among us).

Bascially, what I did was create a new Subscriber class for each field, including province, and then just created a query builder inside each of them to populate their values with those from the preceding fields. The code is shown below.

AddProvinceFieldSubscriber.php

class AddProvinceFieldSubscriber implements EventSubscriberInterface {
    private $factory;
    private $fieldName;
    private $type;

    public function __construct(FormFactoryInterface $factory, $fieldName) {
        $this->factory = $factory;
        $this->fieldName = $fieldName . 'Province';
        $this->type = $fieldName;
    }

    public static function getSubscribedEvents() {
        return array(
            FormEvents::PRE_SET_DATA => 'preSetData',
            FormEvents::PRE_SUBMIT => 'preSubmit',
        );
    }

    private function addProvinceForm(FormInterface $form, $province) {
        $form->add($this->factory->createNamed($this->fieldName, 'entity', $province, array(
            'class' => 'MyThing\MainBundle\Entity\Province',
            'mapped' => false,
            'empty_value' => 'Select a province',
            'query_builder' => function (EntityRepository $repository) {
                $qb = $repository->createQueryBuilder('p');
                return $qb;
            },
            'auto_initialize' => false,
            'attr' => array(
                'class' => 'province ' . $this->type .'-province',
                'data-show' => $this->type . '-city',
            )
        )));
    }

    public function preSetData(FormEvent $event) {
        $form = $event->getForm();
        $data = $event->getData();

        if (null === $data)
            return;

        $fieldName = 'get' . ucwords($this->type) . 'Suburb';
        $province = ($data->$fieldName()) ? $data->$fieldName()->getCity()->getProvince() : null;
        $this->addProvinceForm($form, $province);
    }

    public function preSubmit(FormEvent $event) {
        $form = $event->getForm();
        $data = $event->getData();

        if (null === $data)
            return;

        $province = array_key_exists($this->fieldName, $data) ? $data[$this->fieldName] : null;
        $this->addProvinceForm($form, $province);
    }
}

AddCityFieldSubscriber.php

class AddCityFieldSubscriber implements EventSubscriberInterface {
    private $factory;
    private $fieldName;
    private $provinceName;
    private $suburbName;
    private $type;

    public function __construct(FormFactoryInterface $factory, $fieldName) {
        $this->factory = $factory;
        $this->fieldName = $fieldName . 'City';
        $this->provinceName = $fieldName . 'Province';
        $this->suburbName = $fieldName . 'Suburb';
        $this->type = $fieldName;
    }

    public static function getSubscribedEvents() {
        return array(
            FormEvents::PRE_SET_DATA => 'preSetData',
            FormEvents::PRE_SUBMIT => 'preSubmit',
        );
    }

    private function addCityForm(FormInterface $form, $city, $province) {
        $form->add($this->factory->createNamed($this->fieldName, 'entity', $city, array(
            'class' => 'MyThing\MainBundle\Entity\City',
            'empty_value' => 'Select a city',
            'mapped' => false,
            'query_builder' => function (EntityRepository $repository) use ($province) {
                $qb = $repository->createQueryBuilder('c')
                                ->innerJoin('c.province', 'province');
                if ($province instanceof Province) {
                    $qb->where('c.province = :province')
                       ->setParameter('province', $province);
                } elseif (is_numeric($province)) {
                    $qb->where('province.id = :province')
                       ->setParameter('province', $province);
                } else {
                    $qb->where('province.provinceName = :province')
                       ->setParameter('province', null);
                }

                return $qb;
            },
            'auto_initialize' => false,
            'attr' => array(
                'class' => 'city ' . $this->type . '-city',
                'data-show' => $this->type . '-suburb',
            )
        )));
    }

    public function preSetData(FormEvent $event) {
        $data = $event->getData();
        $form = $event->getForm();

        if (null === $data) {
            return;
        }

        $fieldName = 'get' . ucwords($this->suburbName);
        $city = ($data->$fieldName()) ? $data->$fieldName()->getCity() : null;
        $province = ($city) ? $city->getProvince() : null;
        $this->addCityForm($form, $city, $province);
    }

    public function preSubmit(FormEvent $event) {
        $data = $event->getData();
        $form = $event->getForm();

        if (null === $data)
            return;

        $city = array_key_exists($this->fieldName, $data) ? $data[$this->fieldName] : null;
        $province = array_key_exists($this->provinceName, $data) ? $data[$this->provinceName] : null;
        $this->addCityForm($form, $city, $province);
    }
}

And finally AddSuburbFieldSubscriber.php

class AddSuburbFieldSubscriber implements EventSubscriberInterface {
    private $factory;
    private $fieldName;
    private $type;

    public function __construct(FormFactoryInterface $factory, $fieldName) {
        $this->factory = $factory;
        $this->fieldName = $fieldName . 'Suburb';
        $this->type = $fieldName;
    }

    public static function getSubscribedEvents() {
        return array(
            FormEvents::PRE_SET_DATA => 'preSetData',
            FormEvents::PRE_SUBMIT => 'preSubmit',
        );
    }

    private function addSuburbForm(FormInterface $form, $city) {
        $form->add($this->factory->createNamed($this->fieldName, 'entity', null, array(
            'class' => 'MyThing\MainBundle\Entity\Suburb',
            'empty_value' => 'Select a suburb',
            'query_builder' => function (EntityRepository $repository) use ($city) {
                $qb = $repository->createQueryBuilder('s')
                                ->innerJoin('s.city', 'city');

                if ($city instanceof City) {
                    $qb->where('s.city = :city')
                       ->setParameter('city', $city);
                } elseif (is_numeric($city)) {
                    $qb->where('city.id = :city')
                       ->setParameter('city', $city);
                } else {
                    $qb->where('city.cityName = :city')
                       ->setParameter('city', null);
                }
                    $sql = $qb->getQuery()->getSQL();

                return $qb;
            },
            'auto_initialize' => false,
            'attr' => array(
                'class' => 'suburb ' . $this->type . '-suburb',
            ),
        )));
    }

    public function preSetData(FormEvent $event) {
        $data = $event->getData();
        $form = $event->getForm();

        if (null === $data)
            return;

        $fieldName = 'get' . ucwords($this->fieldName);
        $city = ($data->$fieldName()) ? $data->$fieldName()->getCity() : null;
        $this->addSuburbForm($form, $city);
    }

    public function preSubmit(FormEvent $event) {
        $data = $event->getData();
        $form = $event->getForm();

        if (null === $data)
            return;

        $city = array_key_exists($this->type . 'City', $data) ? $data[$this->type . 'City'] : null;
        $this->addSuburbForm($form, $city);
    }
}

I had to add some extra stuff in there, but you get the gist of it.

In my form type I simply added the following:

$builder
    ->addEventSubscriber(new AddProvinceFieldSubscriber($factory, 'postal'))
    ->addEventSubscriber(new AddCityFieldSubscriber($factory, 'postal'))
    ->addEventSubscriber(new AddSuburbFieldSubscriber($factory, 'postal'))
//...

And happy days! Hope this helps somebody.

Also, I added the data-show attributes to simplify my AJAX process, just in case somebody was wondering.