Submitting an existing block or form in a modal doesn't work

Question

I am trying to open either the simplenews subsription block or the corresponding form in a modal. I tried with both the form using the formBuilder service or the exising plugin-block and in both cases I can successfully load and display the subsription block/form in the modal. The problem now is, that when I enter an email address and try to subscribe i.e. submit the form it doesn't work. I am redirected to my controller ajax callback.

How can I make the form/block work correctly inside the modal?

Answer 1

The standard approach is old-style Drupal with a form alter hook adding a submit handler where you redirect to a different Drupal route:

$form_state->setRedirect('<front>');

You'll find plenty of examples by searching this site or others.

However, looking at the module's code, the form is OOP style, so it would be a better approach to extend the contrib form class and override the submit method:

public function submitExtra(array $form, FormStateInterface $form_state)  {
  parent::submitExtra($form, $form_state);
  $form_state->setRedirect('<front>');
}

Then you can override other things, too, to make a perfect form to place it in modals, like the variants you've already tried for pages and blocks.