SF2, validation dynamique du formulaire avec les FORM EVENTS

SF2, validation dynamique du formulaire avec les FORM EVENTS

 
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;

            $builder->add('date_debut', null, [
                    'constraints' => [
                        new Range(['min' =>  new \Datetime())
                    ]
                ]
            );
            $builder->add('date_fin', null, [
                    'constraints' => [
                        new Range(['min' =>  new \Datetime())
                    ]
                ]
            );
            $builder->addEventListener(
                FormEvents::PRE_SUBMIT,
                function (FormEvent $event) {
                    $data = $event->getData();
                    if (array_key_exists('date_debut', $data) and array_key_exists('date_fin', $data) ) {
                            $event->getForm()->add('fate_fin', 'number', [
                                    'label' => 'date_fin',
                                    'constraints' => [
                                        new Range(['min' =>  $data['date_debut'])
                                    ]
                                ]
                            );
                        }

                    }
                }
            );