States Subscriber for AddressType when Select Countries

AddStateFieldSubscriber.php

<?php

namespace AppBundle\Form\EventListener;

use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\PropertyAccess\PropertyAccess;
use Doctrine\ORM\EntityRepository;

class AddStateFieldSubscriber implements EventSubscriberInterface {

    private $propertyPathToCity;

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

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

    private function addStateForm($form, $country_id, $state = null) {
        $formOptions = array(
            'class' => 'AppBundle:State',
            'empty_value' => 'State',
            'label' => 'State',
            'mapped' => false,
            'attr' => array(
                'class' => 'state_selector form-control',
            ),
            'query_builder' => function (EntityRepository $repository) use ($country_id) {
            $qb = $repository->createQueryBuilder('s')
                    ->innerJoin('s.country', 'c')
                    ->where('c.id = :country')
                    ->orderBy('s.name', 'ASC')
                    ->setParameter('country', $country_id)
                    ;
            return $qb;
            }
        );
        
        if ($state) {
            $formOptions['data'] = $state;
        }
        $form->add('state', 'entity', $formOptions);
    }

    public function preSetData(FormEvent $event) {
        
        $data = $event->getData();
        $form = $event->getForm();
        
        if (null === $data) {
            return;
        }
        
        $accessor = PropertyAccess::createPropertyAccessor();
        
        $city = $accessor->getValue($data, $this->propertyPathToCity);
        $state = ($city) ? $city->getState() : null;
        $country_id = ($state) ? $state->getCountry()->getId() : null;
        
        $this->addStateForm($form, $country_id, $state);
    }

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

        $country_id = array_key_exists('country', $data) ? $data['country'] : null;
        
        $this->addStateForm($form, $country_id);
    }

}