Event

TestFormEvent.php

<?php

namespace Drupal\expert_questions\Form;

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

/**
 * Class TestFormEvent.
 *
 * @package Drupal\expert_questions\Form
 */
class TestFormEvent extends FormBase {

  /**
   * Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher definition.
   *
   * @var \Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher
   */
  protected $eventDispatcher;
  /**
   * Constructs a new TestFormEvent object.
   */
  public function __construct(
    ContainerAwareEventDispatcher $event_dispatcher
  ) {
    $this->eventDispatcher = $event_dispatcher;
  }

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


  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'test_form_event';
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Submit'),
    ];

    return $form;
  }

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

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    // Display result.
    foreach ($form_state->getValues() as $key => $value) {
      drupal_set_message($key . ': ' . $value);
    }

  }

}