How can I programmatically extend the registration form?

Question

I'm trying to extend registration form programatically to add an additional field. I was following an example from Extend _form in Drupal 8

• I created a new service that will redirect to the new form.
• I created a route subscriber to that will return the new form.
• I created a form class that will extend the form.

It works for the user login form but wont work on user registration form because it is an _entity_form and I guess it should be treated differently. I changed the router subscriber to match registration form but i get this error.

Call to a member function getEntityTypeId() on null.

if ($route = $collection->get('user.register')) {$route->setDefault('_entity_form', '\Drupal\form_overwrite\Form\NewUserLoginForm');

Can anyone suggest please what's the right way to extend this form? I tried with the all known hook_form_alter but even like that I'm not sure how to save the new field content in the configuration files.

Answer 1

I had this same question and it doesn't seem to be answered anywhere so I'll give the answer that I figure out, hopefully this helps someone.

First you need to add the form to the entity do this in the module file in hook_entity_type_build something like the following sample:

/**
 * Implements hook_entity_build
 */
function MYMODULE_entity_type_build(array &$entity_types) {

  $entity_types['user']->setFormClass(
    'MYMODULE_register',
    'Drupal\MYMODULE\Form\myModuleRegisterForm'
  );
}

Create a new class src/Form/myModuleRegisterForm.php to extend RegisterForm:

namespace Drupal\MYMODULE\Form;

use Drupal\Core\Form\FormStateInterface;
use Drupal\user\RegisterForm;

class myModuleRegisterForm extends RegisterForm {

  /**
   * {@inheritdoc}
   */
  public function form(array $form, FormStateInterface $form_state) {
        
    $form = parent::form($form, $form_state);

    // Change the form here

    return $form;
  }

}

Then load it in your controller

public function myModuleRegister {

  $build = [];

  $entity = \Drupal::entityTypeManager()
    ->getStorage('user')
    ->create([]);

  $formObject = \Drupal::entityTypeManager()
    ->getFormObject('user', 'MYMODULE_register')
    ->setEntity($entity);

   $build['form'] = \Drupal::formBuilder()->getForm($formObject);

   return $build;
}

That pretty much covers it, obviously you need the route to point to the appropriate function in your controller but otherwise this should do it. Hope it helps.

Answer 2

The other answers focus on overwriting the route itself. If you don't care about changing the route, but just want to change the form markup, here's how to do it:

In your .module file:

function your_module_entity_type_alter(array &$entity_types) {
  $entity_types['user']->setFormClass('register', '\Drupal\your_module\Form\NewRegisterForm');
}

This overrides the Annotations set in User.php

*   handlers = {
 *     "storage" = "Drupal\user\UserStorage",
 *     "storage_schema" = "Drupal\user\UserStorageSchema",
 *     "access" = "Drupal\user\UserAccessControlHandler",
 *     "list_builder" = "Drupal\user\UserListBuilder",
 *     "views_data" = "Drupal\user\UserViewsData",
 *     "route_provider" = {
 *       "html" = "Drupal\user\Entity\UserRouteProvider",
 *     },
 *     "form" = {
 *       "default" = "Drupal\user\ProfileForm",
 *       "cancel" = "Drupal\user\Form\UserCancelForm",
 *       "register" = "Drupal\user\RegisterForm"
 *     },
 *     "translation" = "Drupal\user\ProfileTranslationHandler"
 *   },

The one we're interesting in is the "register" key under "form".

Then in your NewRegisterForm.php you don't need to implement __construct or create, as these are inherited from RegisterForm. In my case, I just wanted to change the submit button text, so I have:

class NewRegisterForm extends RegisterForm {

  protected function actions(array $form, FormStateInterface $form_state) {
    $element = parent::actions($form, $form_state);
    $element['submit']['#value'] = 'Submit';
    return $element;
  }

}

Hope that helps, took me a while to find why overwriting the route didn't do what I wanted.

Answer 3

I had problem with my class throwing an error :

Error: Call to a member function getEntityTypeId() on null in Drupal\Core\Entity\EntityForm->getBaseFormId()

Then I found this code and I think that for Entity form you have to add __construct and create functions:

<?php
namespace Drupal\my_module\Form;

use Drupal\Component\Datetime\TimeInterface;
use Drupal\Core\Entity\EntityFormBuilderInterface;
use Drupal\Core\Entity\EntityManagerInterface;
use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
use Drupal\Core\Extension\ModuleHandlerInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Language\LanguageManagerInterface;
use Drupal\user\Entity\User;
use Drupal\user\RegisterForm;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Provides a user register form.
 */
class NewUserRegisterForm extends RegisterForm {

    public function __construct(EntityManagerInterface $entity_manager, LanguageManagerInterface $language_manager, EntityTypeBundleInfoInterface $entity_type_bundle_info = NULL, TimeInterface $time = NULL, ModuleHandlerInterface $moduleHandler) {
        $this->setEntity(new User([], 'user'));
        $this->setModuleHandler($moduleHandler);

        parent::__construct($entity_manager, $language_manager, $entity_type_bundle_info, $time);
    }

    /**
     * @inheritdoc
     */
    public static function create(ContainerInterface $container) {
        return new static(
            $container->get('entity.manager'),
            $container->get('language_manager'),
            $container->get('entity_type.bundle.info'),
            $container->get('datetime.time'),
            $container->get('module_handler')
        );
    }

    public function form(array $form, FormStateInterface $form_state) {
        $form = parent::form($form, $form_state);
        $form['test'] = [
            '#markup' => '<p>Test extended form</p>',
        ];
        return $form;
    }
} 

Code from David Duymelinck Thanks to him.