Dynamically set field type option readonly to false on choice if dependent radio button is checked true using symfony2

DormerRequestType.php

<?php

use Symfony\Component\Form\AbstractType;

class FooBarType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('addFoo', 'choice', array(
                        'choices' => array(
                            '0' => 'No',
                            '1' => 'Yes'
                        ),
                        'expanded' => true,
                        'required' => true
                    ))
                    ->add('selectFoo', 'entity', array(
                        'class' => 'Acme\AppBundle\Entity\Foo',
                        'attr' => array('readonly' => true)
                    ))
            ;

                $builder->addEventListener(
                    FormEvents::SUBMIT,
                    function(FormEvent $event) use ($options) {
                        $data = $event->getData();
                        $form = $event->getForm();
                        $disabled = $data->getFoo() == '1' ? false : true;

                        $form->add('selectFoo', 'entity', array(
                            'class' => 'Acme\AppBundle\Entity\Foo',
                            'attr' => array('readonly' => $readonly)
                        ));
                    }
                );
    }
}

See: http://symfony.com/doc/current/reference/forms/types/text.html#read-only

Issue:
symfony/symfony#12946

For an easier implementation cross fingers for the field dependent support: symfony/symfony#5807