假设我有产品并且产品可以是promo。单击促销复选框时，我希望显示promoPrice字段。这是我的AbstractType的示例//...//$builder->add(..);$builder->add('promoProduct','checkbox',['required'=>false,]);$builder->add('promoPrice','hidden')//$builder->add(..);$formModifier=function(FormInterface$form,$promoProduct=null){if($promoProduct){$form->a