How to render a checkbox that is checked by default with the symfony2 Form Builder?

Question

I have not found any easy way to accomplish to simply check a Checkbox by default. That can not be that hard, so what am i missing?

Answer 1

To complete a previous answer, with a multiple field you can do that to check all choices :

   'choice_attr' => function ($val, $key, $index) {
       return array('checked' => true);
   }

https://symfony.com/doc/3.3/reference/forms/types/choice.html#choice-attr