Symfony 4表单-如何在子表单中获取父元素的子元素

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\CollectionType;
use Symfony\Component\Form\FormBuilderInterface;

class ParentFormType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            // 添加其他字段
            ->add('children', CollectionType::class, [
                'entry_type' => ChildFormType::class,
                'allow_add' => true,
                'allow_delete' => true,
            ]);
    }
}

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

class ChildFormType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->addEventListener(FormEvents::PRE_SET_DATA, function (FormEvent $event) {
            $form = $event->getForm();
            $parentForm = $form->getParent();
            $children = $parentForm->get('children')->getData();
            
            // 处理父元素的子元素
        });
    }
}