How to add an Event Listener to a dynamically added field using Symfony Forms

Question

I am using event listeners to dynamically modify a form. I want to add another event listener to a field that was added dynamically. Im not sure how to accomplish this.

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder->add('first_field','choice',array(
        'choices'=>array('1'=>'First Choice','2'=>'Second Choice')
    ));

    $builder->addEventListener(FormEvents::PRE_SET_DATA, array($this, 'preSetData'));
    $builder->get('first_field')->addEventListener(FormEvents::POST_SUBMIT, array($this, 'postSubmit'));
}

public function preSetData(FormEvent $event)
{
    $form = $event->getForm();
    $form->add('second_field','choice',array(
        'choices'=>array('1'=>'First Choice','2'=>'Second Choice')
    ));
    //Some how add an event listener to this field

}

public function postSubmit(FormEvent $event)
{
    $form = $event->getForm()->getParent();
    $form->add('second_field','choice',array(
        'choices'=>array('1'=>'First Choice','2'=>'Second Choice')
    ));
    //Some how add an event listener to this field
}

I have trie just using the $builder in the buildForm function to add the event listener to the second_field but because the field doesnt exist when the form is initially generated it throws an error.

If i try and add the new event listener inside the first event listener by doing:

$form->get('second_field')->addEventListener(...)

Then i get the error:

Call to undefined method Symfony\Component\Form\Form::addEventListener() 

Any suggestions would be welcome.

Answer 1

If, is it actually.

FormInterface does't have the addEventListener method, but FormBuilderIntreface have it. If you want to add any listener, you should to create form field by form builder.

For example:

   // create builder for field
   $builder = $form->getConfig()->getFormFactory()->createNamedBuilder($name, $type, null, array(
       /** any options **/
       'auto_initialize'=>false // it's important!!!
   ));
   // now you can add listener
   $builder->addEventListener(FormEvents::POST_SUBMIT, $yourCallbackHere)

   // and only now you can add field to form  
   $form->add($builder->getForm());