Symfony2 - How to use a Data Transformer inside EventListeners

Question

• I need to use an Event Listener since I need different things to be displayed in my form whether it is new or an already existing entity. I can manage that.

Answer 1

Short answer: You can´t add the transformer inside the listener because the form is already locked.

Long answer: There are some solutions. The most common, at least for me, is to a create a Custom form type where you add your transformer. Then you add your custom form how you would normally do in the event listener:

class ElementCustomType extends AbstractType {

    private $em;

    public function __construct(EntityManager $entityManager)
    {
        $this->em = $entityManager;
    }

    public function buildForm(FormBuilderInterface $builder, array $options) {

        $builder
            ->addModelTransformer(new ElementObjToStringTransformer($this->em))
        ;
    }

    public function getParent() {
        return 'text';
    }

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

Define your form as a service:

 app.form.type.custom_element:
    class: AppBundle\Form\Type\ElementCustomType
    arguments: [@doctrine.orm.entity_manager]
    tags:
        - { name: form.type, alias: elementCustom }

Use the form in the listener as your would normally do:

$builder->addEventListener(FormEvents::PRE_SET_DATA, function(FormEvent $event){
        $element = $event->getData();
        $form = $event->getForm();
        $form->add('element', 'elementCustom')
    });