如何将if添加到Symfony中的表单生成器中

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\OptionsResolver\OptionsResolver;

class MyFormType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('field1')
            ->add('field2')
            ->addEventListener(FormEvents::PRE_SET_DATA, function (FormEvent $event) {
                $form = $event->getForm();
                $data = $event->getData();

                if ($data && $data->getField1() === 'some_value') {
                    $form->add('field3');
                }
            });
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'data_class' => 'App\Entity\YourEntity',
        ]);
    }
}

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;

class MyController extends AbstractController
{
    public function myAction(Request $request)
    {
        $form = $this->createForm(MyFormType::class);

        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            // 处理表单提交
        }

        return $this->render('my_template.html.twig', [
            'form' => $form->createView(),
        ]);
    }
}

{{ form_start(form) }}
{{ form_row(form.field1) }}
{{ form_row(form.field2) }}
{{ form_row(form.field3) }}
{{ form_end(form) }}