symfony modify choices in collection after set data - symfony

Question

I'm trying to build a form, for user to enter his answers to an exam.
Form consists of Collection of answers looking like this:
class UserExamFormType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('answers', CollectionType::class,
[
'entry_type' => UserExamAnswerType::class,
'allow_delete' => false,
'allow_add' => false,
])->add('submit', SubmitType::class,
[
'label' => 'Zapisz',
'attr' => [
'class' => 'btn-success',
],
]
)->add('finish', SubmitType::class,
[
'label' => 'Zapisz i zakończ',
'attr' => [
'class' => 'btn-danger confirmation',
'data-message' => 'Czy na pewno chcesz zakończyć test? Nie będzie możliwości poprawy odpowiedzi.'
],
]
);
}
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults([
'data_class' => UserExam::class,
]);
}
}
class UserExamAnswerType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
// dump($builder->getData()); === null
$builder
->add('answer', EntityType::class,
[
'class' => Answer::class,
'choice_value' => 'id',
'expanded' => true,
'query_builder' => function (EntityRepository $entityRepository) {
return $entityRepository->createQueryBuilder('a');
}
]);
$builder->addEventListener(FormEvents::POST_SET_DATA, function (FormEvent $event) {
dump($event->getData()); // !== null
//modify choices
});
}
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults([
'data_class' => ExamAnswer::class,
]);
}
}
How to modify choices in the commented line?
I'd like the choices to be affected by the object passed into the form.
In the line dump($event->getData()); // !== null I get exactly the object I need to determine choices but I haven't found any info on it - only dynamically adding a field.

Answer 1

I finally made it by adding an element right before Symfony sets the data on form.
Maybe someone will profit from this:
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder->addEventListener(FormEvents::PRE_SET_DATA, function (FormEvent $event) {
$event->getForm()
->add('answer', EntityType::class,
[
'class' => Answer::class,
'choice_value' => 'id',
'expanded' => true,
'choices' => $event->getData()->getQuestion()->getAnswers()
]);
});
}