Symfony form: set options according to the data

ContextualOptionsFormListener.php

<?php
namespace AppBundle\Form\EventListener;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;

class ContextualOptionsFormListener implements EventSubscriberInterface
{
    /**
     * @var callable
     */
    private $callback;

    /**
     * The callback will be called for each child of the listened form.
     * The callback will receive the following params:
     *  - FormEvent $event
     *  - $name name of the child
     *  - array $options the initial options of the child
     * The callback must return an array with the final options of the child.
     *
     * @param callable $callback
     */
    public function __construct(callable $callback)
    {
        $this->callback = $callback;
    }

    /**
     * @return array The event names to listen to
     */
    public static function getSubscribedEvents()
    {
        return [
            FormEvents::PRE_SET_DATA => 'preSetData',
        ];
    }

    /**
     * @param FormEvent $event
     */
    public function preSetData(FormEvent $event)
    {
        $form = $event->getForm();
        $data = $event->getData();

        if (null === $data) {
            return;
        }

        $children = $form->all();

        foreach ($form as $name => $child) {
            $form->remove($name);
        }

        foreach ($children as $name => $child) {
            $form->add(
                $name,
                $child->getConfig()->getType()->getInnerType(),
                call_user_func($this->callback, $event, $name, $child->getConfig()->getOptions())
            );
        }
    }
}

Example.php

<?php
namespace AppBundle\Model;

class Example
{
    public $value;

    public function isDisabled()
    {
        return $this->value === 'disabled';
    }
}

ExampleController.php

<?php
namespace AppBundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use AppBundle\Model\Example;
use AppBundle\Model\Form\Type\ExampleType;

class ExampleController extends Controller
{
    /**
     * @Route("/")
     * @return \Symfony\Component\HttpFoundation\RedirectResponse
     */
    public function indexAction()
    {
        $example = new Example();
        $example->value = 'disabled';
      
        $form = $this->createForm(ExampleType::class, $example);
        
        ...
    }
}

ExampleType.php

<?php
namespace AppBundle\Form\Type;

use Symfony\Component\Form\AbstractType;
use AppBundle\Form\EventListener\ContextualOptionsFormListener;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormEvent;

class ExampleType extends AbstractType
{

    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('value');
      
        $builder->addEventSubscriber(new ContextualOptionsFormListener(
            function (FormEvent $event, $name, array $options) {
                if ($name === 'value') {
                    //the "value" field will be conditionnaly disabled according to Example instance.
                    $options['disabled'] = $event->getData()->isDisabled();
                }
                return $options;
            }
        ));
    }
}

The goal:

You want to set some options conditionnally, according to the data given.

The problem:

1. The data given to the FormBuilder is not available in the method buildForm (You can retrieve it with $options['data'], but only in the parent form, not in the children).
2. The config of the form is early locked, and it is not possible to use events such PRE_SET_DATA: https://knpuniversity.com/screencast/question-answer-day/symfony2-conditionally-required-field#a-solution-that-doesn-t-work-event-listeners

The solution here

We loop on each child and reset it with a callback that can modify the options according to the data.