How to pass variables to OpenModalDialogCommand

Question

Drupal 8. Clicking the upload button on Form1 should open UploadForm in a modal dialog.

/**
 * Callback to display a modal.
 */
public function ajaxSubmit(&$form, FormStateInterface $form_state) {
  $op = $form_state->getTriggeringElement()['#return_value'];
  switch ($op) {
    case 'upload':
      $modal = new OpenModalDialogCommand(
        t('Upload file(s)'), 
          render(\Drupal::formBuilder()->getForm('UploadForm', 
            $this->nid, $this->foo, $this->bar))));
      break;

    // ... other cases.
  }

  $response = new AjaxResponse();
  $response->setAttachments($form['#attached']);
  $response->addCommand($modal);
  return $response;
}

I'm not able to pass the variables to UploadForm. $this-> properties don't appear in UploadForm.

\Drupal::formBuilder()->getForm('UploadForm', $this->nid, $this->foo, $this->bar));

The form also fails if I replace the variables by local variables

$nid, $foo, $bar

But it works when I replace them by

'28', 'foo', 'bar'

The non-ajax version of the form uses a redirect to a form route (my_module.uploadform) and works OK. Is there a way to pass the parameters to UploadForm?

Answer 1

Solved. Thanks @kiamlaluno. I was convinced the variables were OK. But after your comment and a fresh look I saw what I was missing: $this->nid, $this->foo, $this->bar are optional parameters for the UploadForm formbuilder. I was passing only nid and bar, but missing foo, which messed-up things. So, instead of:

\Drupal::formBuilder()->getForm('UploadForm', $this->nid, $this->bar) //don't need foo

I needed to call:

\Drupal::formBuilder()->getForm('UploadForm', $this->nid, null, $this->bar)

A bit obvious, I'm afraid...