FormTestObject.php

<?php

declare (strict_types=1);
namespace Drupal\form_test;

use Drupal\Core\Form\ConfigFormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Provides a test form object.
 *
 * @internal
 */
class FormTestObject extends ConfigFormBase {
  
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'form_test_form_test_object';
  }
  
  /**
   * {@inheritdoc}
   */
  protected function getEditableConfigNames() {
    return [
      'form_test.object',
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['element'] = [
      '#markup' => 'The FormTestObject::buildForm() method was used for this form.',
    ];
    $form['bananas'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Bananas'),
    ];
    $form['strawberry'] = [
      '#type' => 'hidden',
      '#value' => 'red',
      '#attributes' => [
        'id' => 'red-strawberry-hidden-field',
      ],
    ];
    $form['actions']['#type'] = 'actions';
    $form['actions']['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Save'),
    ];
    $form['#title'] = 'Test dynamic title';
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    $this->messenger()
      ->addStatus($this->t('The FormTestObject::validateForm() method was used for this form.'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $this->messenger()
      ->addStatus($this->t('The FormTestObject::submitForm() method was used for this form.'));
    $this->config('form_test.object')
      ->set('bananas', $form_state->getValue('bananas'))
      ->save();
  }

}