symfony 3.4 : forms : Use Data Transformers - forms

Question

trying to use data transformer, I have an error when loadding my html form
In my formType class
use Doctrine\ORM\EntityManagerInterface;
class PmpType extends AbstractType
{
private $entityManager;
public function __construct(EntityManagerInterface $entityManager)
{
$this->entityManager = $entityManager;
}
}
in my app\config\services.yml
services:
# default configuration for services in *this* file
_defaults:
# automatically injects dependencies in your services
autowire: true
# automatically registers your services as commands, event subscribers, etc.
autoconfigure: true
# this means you cannot fetch services directly from the container via $container->get()
# if you need to do this, you can override this setting on individual services
public: true
but I received this error
Type error: Too few arguments to function myApp\Bundle\Form\PmpType::__construct(), 0 passed in \vendor\symfony\symfony\src\Symfony\Component\Form\FormRegistry.php on line 92 and exactly 1 expected
What do I miss
Thx for hepl

Answer 1

OK
I don't understand why but I have toset the service for my class :
in service.yml, I add
seims_pmp.pmptype:
class: SEISM\PmpIG56Bundle\Form\PmpType
arguments: ["#doctrine.orm.entity_manager"]
tags: [form.type]
and now it's working