我不能在createFormBuilder中使用变量

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

class MyDynamicFormType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $formName = $options['form_name'];

        $builder
            ->add('field1', TextType::class)
            ->add('field2', TextType::class)
            // 添加其他字段
        ;
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'form_name' => 'default_form_name',
        ]);
    }
}

$form = $this->createForm(MyDynamicFormType::class, null, [
    'form_name' => 'dynamic_form_name',
]);