messenger()->addMessage not working after a $form_state->setResponse

Question

In the submitForm of a custom form, I have this:

switch ($form_state->getValue('suscribe')) {
  case 0:
    $iStatus = 1;
    break;
  case 1:
    $iStatus = 3;
    $sFileName = 'sites/default/files/_private/bulletins/' . $form_state->getValue('adherent')[1] . ".pdf";
    $response = new BinaryFileResponse($sFileName);
    $response->setContentDisposition(
      ResponseHeaderBag::DISPOSITION_ATTACHMENT,
      'bulletin.pdf'
    );
    $form_state->setResponse($response);
    break;
}

$storage = \Drupal::entityTypeManager()->getStorage('member');
$id = $form_state->getValue('adherent')[0];
$entity = $storage->load($id);
$entity->status = $iStatus;
$entity->save();

\Drupal::messenger()->addMessage($this->t('Your wish has been recorded.'));

suscribe is a Yes/No radio button.
$form_state->setResponse($response); triggers the automatic download of a pdf document.

The message (Your wish...) is correctly displayed in case 0.
In case 1, the message shows only if I refresh the page (or go to another page).
How can I have the message displayed without doing another action after submitting the form in case 1?

By the way, database is correctly updated in both cases.
I'm using Drupal 8.6.10.

Answer 1

How can I have the message displayed without doing another action after submitting the form in case 1?

You can't - when you force download a file the page you see behind it is the original form request, and always will be. It's just how browsers work.

You'll need to refresh the page (or visit a new page) to see the messages, which haven't been rendered as part of the force-download request, and so are still sitting in the session waiting to be rendered.

You might be able to hack something together with JS to make this work, but in my experience it's not worth the hassle. The browser doesn't even report back to you when the file is downloaded (what if it isn't? What if the user cancels or there are network problems?), so it's a real pain to implement.

Answer 2

Finally and using advice from @Clive, I made it this way:

  public function submitForm(array &$form, FormStateInterface $form_state)
  {
    switch ($form_state->getValue('suscribe')) {
      case 0:
        $iStatus = 1;
        $sMessage = $this->t('Your wish has been recorded.');
        break;
      case 1:
        $iStatus = 3;
        $Url = Url::fromUri('base:/association/membership/download/' . $form_state->getValue('adherent')[0]);
        $sLink = \Drupal\Core\Link::fromTextAndUrl($this->t('here'), $Url)->toString();
        $sMessage = $this->t('Your wish has been recorded.<BR>To download your membership form, please click %link.', ['%link' => $sLink]);
        break;
    }
    $storage = \Drupal::entityTypeManager()->getStorage('member');
    $id = $form_state->getValue('adherent')[0];
    $entity = $storage->load($id);
    $entity->status = $iStatus;
    $entity->save();
    \Drupal::messenger()->addMessage($sMessage);
  }

which gives

Case 0: a simple message saying that wish has been recorded.

Case 1: the same message plus a link to download the document

In association.routing.yml:

association.membership_download:
  path: '/association/membership/download/{member}'
  defaults:
    _controller: '\Drupal\association\Controller\MembershipController::download'
  requirements:
    _permission: 'renew membership'  

In MembershipController.php:

  public function download($member)
  {

    $storage = \Drupal::entityTypeManager()->getStorage('member');
    $entity = $storage->load($member);
    $sFileName = 'sites/default/files/_private/bulletins/' . $entity->designation->value . '.pdf';
    $response = new BinaryFileResponse($sFileName);
    $response->setContentDisposition(
      ResponseHeaderBag::DISPOSITION_ATTACHMENT,
      'bulletin.pdf'
    );
    return $response;
  }