how to add validation to unbound form field in symfony2

Question

I am trying to validate an unbound field in my symfony2 form.

I have googled it and found several similar solutions, so I did a copy-paste and put my own stuff in th

Answer 1

CallbackValidator FQCN should be Symfony\Component\Form\CallbackValidator .

Answer 2

So, for anyone else needing validation for unbound form fields in symfony 2 here Is how I ended up doing it - turned out I was missing a bunch of use statements, they weren't listed on any of the sites where I found other threads on the subject.

I have weeded out everything but the essentials. Thanks to m2mdas for helping me along on this one.

<?php

namespace BizTV\UserBundle\Form;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilder;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\Form\CallbackValidator;
use Symfony\Component\Form\FormValidatorInterface;
use Symfony\Component\Form\FormError;


use Doctrine\ORM\EntityRepository;

class newServerType extends AbstractType
{

    public function buildForm(FormBuilder $builder, array $options)
    {   
        $builder->add('screenName', null, array('property_path' => false, 'label' => 'Namn på skärmen (användaren kan ändra det senare) '));

        $builder-> addValidator(new CallbackValidator(function(FormInterface $form){
          $screenName = $form->get('screenName')->getData();
            if (empty($screenName)) {
              $form['screenName']->addError(new FormError("Du måste ange ett namn för den nya skärmen"));
            }
        }));    
    }

    public function getName()
    {
        return 'biztv_userbundle_newservertype';
    }
}