Symfony3, how to load an external choice list in a form?

Question

I don't know if I'm facing a bug or doing something wrong. I'm trying to load choices for a ChoiceType form from a custom class, but I get the following error:

Catchable Fatal Error: Argument 1 passed to Symfony\Component\Form\ChoiceList\LazyChoiceList::__construct() must be an instance of Symfony\Component\Form\ChoiceList\Loader\ChoiceLoaderInterface, none given

My custom class:

<?php
namespace AppBundle\Form\ChoiceLists;

use Symfony\Component\Form\ChoiceList\SimpleChoiceList;
use Symfony\Component\Form\ChoiceList\LazyChoiceList;

class DepartmentsChoiceList extends LazyChoiceList
{
    public function loadChoiceList()
    {
         $choices = array(
             '01' => "Ain",
             '02' => "Aisne",
             '03' => "Allier",
             '04' => "Alpes de Haute Provence",
             '05' => "Alpes (Hautes)",
             //....
             '94' => "Val de Marne",
             '95' => "Val d&acute;Oise",
             '98' => "Mayotte",
             '9A' => "Guadeloupe",
             '9B' => "Guyane",
             '9C' => "Martinique",
             '9D' => "R&eacute;union",
             );
         return new SimpleChoiceList($choices);
    }
}

And in my formType:

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('birthDepartment', ChoiceType::class, array(
            'label' => 'Département :',
            'required' => false,
            'choices' => new DepartmentsChoiceList(),
         )
     );

I found very few documentation for this feature.

Answer 1

Here is my procedure on Symfony 5.4. It may not be the best way to do it, but it's the only one I found that works.

<?php

namespace App\Form;

use App\Controller\ApiController;

use Symfony\Component\Form\ChoiceList\Loader\ChoiceLoaderInterface;
use Symfony\Component\Form\ChoiceList\ArrayChoiceList;

class DepartmentChoiceList implements ChoiceLoaderInterface
{

    public function loadChoiceList($value = null)
    {
        $choices = array(
            '01' => "Ain",
            '02' => "Aisne",
            '03' => "Allier",
            '04' => "Alpes de Haute Provence",
            '05' => "Alpes (Hautes)",
            //....
            '94' => "Val de Marne",
            '95' => "Val d&acute;Oise",
            '98' => "Mayotte",
            '9A' => "Guadeloupe",
            '9B' => "Guyane",
            '9C' => "Martinique",
            '9D' => "R&eacute;union",
        );
        return new ArrayChoiceList($choices);
    }


    public function loadChoicesForValues(array $values, $value = null)
    {
        $result = [];

        return $result;
    }

    public function loadValuesForChoices(array $choices, $value = null)
    {
        $result = [];

        return $result;
    }
}

And formType

public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $builder
            ->add('department', ChoiceType::class, [
                'label' => 'Department',
                'choice_loader' => new DepartmentChoiceList(),
                'constraints' => [
                    new NotBlank(),
                ],
            ])
            ->add('save', SubmitType::class)
        ;
    }