Symfony2 表单事件侦听器和数据转换器错误 无法实例化接口原则..对象管理器

我正在开发一个Symfony 2.3表单，该表单要求字段仅在"创建新"模式下可用。

该字段是多对一关系中的链接，我已经设法通过使用jQuery自动完成功能更改下拉列表，以便通过FormEvents::PRE_SET_DATA事件轻松使用，但是将提供的ID转换为对象的FormEvents::PRE_SUBMIT需要Doctrine ObjectManager。这变成了一个接口，并抛出"无法实例化接口原则''通用''持久性''对象管理器"。
我已经查看了以下类似的问题和文档（表单事件，表单事件下拉列表，Doctrine数据转换器，动态表单修改），但是如此接近尾声（以及PHP和symfony的新手），我不希望重写这篇文章。

您可以在下面找到我的事件侦听器和数据转换器类：

namespace XXXXXXXBundle'Form'EventListener;
use Doctrine'Common'Persistence'ObjectManager;
use Symfony'Component'Form'FormEvents;
use Symfony'Component'EventDispatcher'EventSubscriberInterface;
use XXXXXXXXXXXXXBundle'Form'DataTransformer'rneToEcoleTransformer;
class AddFieldSubscriber implements EventSubscriberInterface {
private $manager;
public static function getSubscribedEvents() {
    // Tells the dispatcher that you want to listen on the form.pre_set_data
    // event and that the preSetData method should be called.
    return array('Symfony'Component'Form'FormEvents::PRE_SET_DATA => 'preSetData',
        'Symfony'Component'Form'FormEvents::PRE_SUBMIT => 'preSubmit');
}
public function preSetData('Symfony'Component'Form'FormEvent $event) {
    $parents = $event->getData();
    $form = $event->getForm();
    //Verifie si le parent d'eleve est un nouveau 
    //ou s'il s'agit d' une mise à jour
    if (!$parents || null === $parents->getId()) {
        $form->add('ecole', 'text', array('invalid_message' => 'Ce RNE n''est pas valide',
            'attr' => array('data-id' => 'ecoles',
                'data-url' => 'parents_json_ecoles'
            )
                )
        );
    }
}
public function preSubmit('Symfony'Component'Form'FormEvent $event) {
    $this->manager = new 'Doctrine'Common'Persistence'ObjectManager;
    $parents = $event->getData();
    if (empty($parents['ecole'])) {
        return;
    }
    $event->getForm()->get('ecole')->getConfig()->addModelTransformer(new rneToEcoleTransformer($this->manager));
}}
namespace XXXXXXXBundle'Form'DataTransformer;
use Symfony'Component'Form'DataTransformerInterface;
use Symfony'Component'Form'Exception'TransformationFailedException;
class rneToEcoleTransformer implements DataTransformerInterface {
private $manager;
public function __construct('Doctrine'Common'Persistence'ObjectManager $manager) {
    $this->manager = $manager;
}

public function transform($ecole) {
    if (null === $ecole) {
        return '';
    }
    return $ecole->getRne();
}

public function reverseTransform($rneNumber) {
    if (!$rneNumber) {
        return;
    }
    $ecole = $this->manager
            ->getRepository('XXXXXXXBundle:Ecole')
            ->find($rneNumber);
    if (null === $ecole) {
          throw new TransformationFailedException(sprintf(
                'No matching data was found "%s" !', $rneNumber
        ));
    }
    return $ecole;
}}

以下是使用的操作：

private function createCreateForm(Parents $entity) {
    $manager = $this->getDoctrine()->getManager();
    $form = $this->createForm(new ParentsType($manager), $entity, array(
        'action' => $this->generateUrl('parents_create'),
        'method' => 'POST',
    ));
    $form->add('submit', 'submit', array('label' => 'Add'));
    return $form;
}

表格类型 ：

class XXXXType extends AbstractType {
private $manager;
public function __construct('Doctrine'Common'Persistence'ObjectManager $manager) {
    $this->manager = $manager;
}
/**
 * @param FormBuilderInterface $builder
 * @param array $options
 */
public function buildForm(FormBuilderInterface $builder, array $options) {
    $builder
            ->add('nom', 'text', array('label' => 'Nom *',
                'attr' => array('placeholder' => 'Nom ',
                    'maxlength' => 250,
                    'trim' => true)
                    )
            )
            ->add('prenoms', 'text', array('label' => 'Prénom(s) *',
                'attr' => array('placeholder' => 'Prénom(s)',
                    'maxlength' => 250,
                    'trim' => true)
                    )
            )
            ->add('date_de_naiss', 'date', array('widget' => 'single_text', 'format' => 'dd-MM-yyyy',
                'label' => 'Date de naissance ',
                'required' => false, 'data' => null,
                'attr' => array('name' => 'datepicker')
                    )
            )
            ->add('telephone', 'text', array('label' => 'Telephone *',
                'attr' => array('placeholder' => '123-456-7890 or 1234567890')
                    )
            )
            ->add('email', 'email', array('attr' => array('placeholder' => 'xxxx@xxxx.com',),
                'trim' => true,
                'required' => false,
                'data' => null
                    )
                  );

    $builder->addEventSubscriber(new AddFieldSubscriber($manager));
}
/**
 * @param OptionsResolverInterface $resolver
 */
public function setDefaultOptions(OptionsResolverInterface $resolver) {
    $resolver->setDefaults(array(
        'data_class' => 'XXXXXXBundle'Entity'Parents'
    ));
}
/**
 * @return string
 */
public function getName() {
    return 'XXXXXXXXXsbundle_parents';
}
}