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

i using event listeners dynamically modify form. want add event listener field added dynamically. im not sure how 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 event listener 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 event listener field } 

i have trie using $builder in buildform function add event listener second_field because field doesnt exist when form generated throws error.

if try , add new event listener inside first event listener doing:

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

then error:

call undefined method symfony\component\form\form::addeventlistener()  

any suggestions welcome.

if, actually.

forminterface does't have addeventlistener method, formbuilderintreface have it. if want add listener, should create form field form builder.

for example:

   // create builder field    $builder = $form->getconfig()->getformfactory()->createnamedbuilder($name, $type, null, array(        /** options **/        'auto_initialize'=>false // it's important!!!    ));    // can add listener    $builder->addeventlistener(formevents::post_submit, $yourcallbackhere)     // , can add field form      $form->add($builder->getform());