Symfony 3.4 - 有没有办法为ChoiceType创建自动递增ID？

I have a ChoiceType that is rendered as a series of radio buttons:

foreach ($cards as $card) {
    $choices["{$card->brand} **** **** **** {$card->last4}"] = $card->id;
}

$form = $this->createFormBuilder()
    ->add('card', ChoiceType::class, ['choices' => $choices,'expanded' => true, 'multiple' => false])
    ->add('Submit', SubmitType::class)
    ->getForm()

I'd like to have an incrementing id for each choice, something like 'card1', 'card2', etc., but am unsure how to actually do it. The choices themselves are dynamically created - I don't know ahead of time how many choices (if any) will be present.

Ideally, there'd be some kind of internal counter I could access in 'choice_attr' and/or 'choice_label', but I don't see anything like that in the docs. Any ideas?

Create a counter variable outside and count it for each of your choices. For adding the id use the choice_attr option:

$i = 0;

$form = $this->createFormBuilder()
    ->add('card', ChoiceType::class, [
        'choices' => $choices,
        'choice_attr' => function() use ($i) {
            $i++;
            return ['id' => 'choice-'.$i];
        },
    ])