class AjaxTestDialogForm

class AjaxTestDialogForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'ajax_test_dialog_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['button1'] = [
            '#type' => 'submit',
            '#name' => 'button1',
            '#value' => 'Button 1 (modal)',
            '#ajax' => [
                'callback' => '::modal',
            ],
        ];
        $form['button2'] = [
            '#type' => 'submit',
            '#name' => 'button2',
            '#value' => 'Button 2 (non-modal)',
            '#ajax' => [
                'callback' => '::nonModal',
            ],
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $form_state->setRedirect('ajax_test.dialog_contents');
    }
    
    /**
     * AJAX callback handler for AjaxTestDialogForm.
     */
    public function modal(&$form, FormStateInterface $form_state) {
        return $this->dialog(TRUE);
    }
    
    /**
     * AJAX callback handler for AjaxTestDialogForm.
     */
    public function nonModal(&$form, FormStateInterface $form_state) {
        return $this->dialog(FALSE);
    }
    
    /**
     * Util to render dialog in ajax callback.
     *
     * @param bool $is_modal
     *   (optional) TRUE if modal, FALSE if plain dialog. Defaults to FALSE.
     *
     * @return \Drupal\Core\Ajax\AjaxResponse
     *   An ajax response object.
     */
    protected function dialog($is_modal = FALSE) {
        $content = AjaxTestController::dialogContents();
        $response = new AjaxResponse();
        $title = $this->t('AJAX Dialog & contents');
        // Attach the library necessary for using the Open(Modal)DialogCommand and
        // set the attachments for this Ajax response.
        $content['#attached']['library'][] = 'core/drupal.dialog.ajax';
        if ($is_modal) {
            $response->addCommand(new OpenModalDialogCommand($title, $content));
        }
        else {
            $selector = '#ajax-test-dialog-wrapper-1';
            $response->addCommand(new OpenDialogCommand($selector, $title, $content));
        }
        return $response;
    }

}