Symfony: How to Dynamically Modify Forms Using Form Events

Question

I'm trying to dynamically add a new input field using the official cookbook tutorial:

http://symfony.com/doc/2.8/cookbook/form/dynamic_form_modification.html#dynamic-generation-for-submitted-forms

but using POST_SUBMIT event (as the official tutorial suggests) I get the following error:

You cannot add children to a submitted form

Answer 1

Take a look at Form Events docs . The last event you can use for modifying the form is FormEvents::PRE_SUBMIT event.