CallbackValidator example

MyType.php

<?php

namespace Acme\DemoBundle\Form;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormError;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\Form\FormError;
use Symfony\Component\Form\CallbackValidator;

class MyType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->addValidator(new CallbackValidator(function (FormInterface $form) {
	    if (!$form['foo']->getData()) {
	        $form['foo']->addError(new FormError('foo.error'));
            }
        }));
    }
    
    // ...
}