Render custom field from user registration form

Question

I'm trying to render a custom field that shows up on the user registration form on a separate new form that creates users of a particular role with specific permissions.

I have everything working except being able to render this custom field.

When I view the field under the user registration form settings page, it says it's an entity reference field. When it renders it has 4 check boxes.

I've figured out how to kint out the fields that are on the user registration form from my new form, but I can't figure out how to render the specific one that I need.

$entityTypeManager = \Drupal::service('entity_field.manager');
$fields = $entityTypeManager->getFieldDefinitions('user', 'user');

foreach ($fields as $field_name) {
  kint($field_name);
}

That gives me a listing of all of the fields in the user registration.

I feel like I'm missing something very obvious.

Answer 1

A form mode is configuration which you can roll out via CMI (drush cex/cim) or install with the module by including the YAML files in the modules config folder.

Implementing a new register form mode is not very intuitive. The basics:

1. Create the form mode:

   /admin/structure/display-modes/form
   

2. Enable and configure it like in this questions for the pre-installed Register form mode:

   How to hide custom fields on the registration form?

3. To place the new form mode on a page you need either a contrib module

   https://www.drupal.org/project/form_mode_manager

   or custom code:

   How do I load a form with a specific form display (form mode)?

   or a custom route:

   mymodule.routing.yml

   mymodule.register2:
     path: '/admin/people/ch-create'
     defaults:
       _entity_form: 'user.register2'
       _title: 'Create new account'
     requirements:
       _permission: 'register certain users'
   

   register2 needs to be registered as form handler in the entity type:

   mymodule.module

   function mymodule_entity_type_build(array &$entity_types) {
     $entity_types['user']->setFormClass('register2', 'Drupal\user\RegisterForm');
   }