updated gist for readonly form field

example

<?php

namespace CustomBundle\Form;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\Extension\Core\Type\CheckboxType;

class ExampleFormType extends AbstractType
{
    /**
     * {@inheritdoc}
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
                ->add('unmappedField', CheckboxType::class, [
                    'attr' => [
                        'disabled' => 'disabled',
                        'readonly' => 'readonly',
                    ],
                ])
        ;
      
        // other fields
        
        $builder->get('unmappedField')
                ->addEventListener(FormEvents::SUBMIT, [$this, 'setUnmappedField']);
    }
    
    public function setUnmappedField(FormEvent $event)
    {
        $formField = $event->getForm();
        $entity = $formField->getParent()->getData();
        
        if($entity) {
            $event->setData($entity->getUnmappedField());
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'CustomBundle\Entity\ExampleEntity',
        ));
    }

    /**
     * {@inheritdoc}
     */
    public function getBlockPrefix()
    {
        return 'custombundle_example';
    }


}