class FormTestControllerObject

class FormTestControllerObject extends ConfigFormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_test_form_test_controller_object';
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getEditableConfigNames() {
        return [
            'form_test.object',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        \Drupal::messenger()->addStatus(t('The FormTestControllerObject::create() method was used for this form.'));
        return new static($container->get('config.factory'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state, Request $request = NULL, $custom_attributes = NULL) {
        $form['element'] = [
            '#markup' => 'The FormTestControllerObject::buildForm() method was used for this form.',
        ];
        $form['custom_attribute']['#markup'] = $custom_attributes;
        $form['request_attribute']['#markup'] = $request->attributes
            ->get('request_attribute');
        $form['bananas'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Bananas'),
        ];
        $form['actions']['#type'] = 'actions';
        $form['actions']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Save'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        $this->messenger()
            ->addStatus($this->t('The FormTestControllerObject::validateForm() method was used for this form.'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->messenger()
            ->addStatus($this->t('The FormTestControllerObject::submitForm() method was used for this form.'));
        $this->config('form_test.object')
            ->set('bananas', $form_state->getValue('bananas'))
            ->save();
    }

}