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Pattern: Standard Form (FormBase)

When to Use

Use FormBase for general-purpose forms with custom business logic. Use ConfigFormBase for settings, EntityForm for entities, ConfirmFormBase for confirmations.

Decision

Situation Choose Why
Authentication, calculations, integrations FormBase Full control, service injection
Configuration management ConfigFormBase Auto config sync
Entity create/edit EntityForm Entity-specific features
Confirmation dialogs ConfirmFormBase Standard UI

Pattern

Dependency injection via create() method:

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;

class MyForm extends FormBase {
  protected $entityTypeManager;

  public function __construct(EntityTypeManagerInterface $entity_type_manager) {
    $this->entityTypeManager = $entity_type_manager;
  }

  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('entity_type.manager')
    );
  }

  public function getFormId() {
    return 'my_module_form';
  }

  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['field'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Field'),
      '#required' => TRUE,
    ];
    return $form;
  }

  public function submitForm(array &$form, FormStateInterface $form_state) {
    $value = $form_state->getValue('field');
    $form_state->setRedirect('route.name');
  }
}

Value Storage

Phase Pattern Purpose
Build $form['field']['#default_value'] = $value Initial display value
Submit $value = $form_state->getValue('field') Submitted value
Cross-rebuild $form_state->set('data', $value) Persist across rebuilds

Common Mistakes

  • Wrong: Not implementing unique getFormId() → Right: Unique ID per form
  • Wrong: Using $_POST directly → Right: Use $form_state->getValue() (CSRF-protected)
  • Wrong: No dependency injection → Right: Use create() for services
  • Wrong: Forgetting parent::buildForm() → Right: Call parent when needed

See Also