How do I redirect on flag save programmatically?

Question

I want to redirect users to a view when they flag a taxonomy term.

This question is about how to use Rules to redirect on flag save. I want to do this programmatically.

I tried to use hook_form_alter() to add a submit handler with the redirect. Unfortunately, while flaggings have an edit form that can be targeted by hook_form_alter() (MYMODULE_form_flagging_FLAGTYPE_edit_form_alter()), they do not seem to have a "create" form.

So how can I add a redirect programmatically upon flagging?

EDIT

Based on 4k4's comment I looked at /flag/srs/Entity/Flagging.php:

 *    "form" = {
 *      "add" = "Drupal\flag\Form\FlaggingForm",
 *      "edit" = "Drupal\flag\Form\FlaggingForm",
 *      "delete" = "Drupal\flag\Form\UnflagConfirmForm"

However, when I tried to do a hook_form_alter() with:

• function MYMODULE_form_flagging_FLAGGINGTYPE_add_form_alter(&$form, FormStateInterface $form_state, $form_id)
• function MYMODULE_form_flagging_add_form_alter(&$form, FormStateInterface $form_state, $form_id)

I could not get either to pick up my code (I rebuilt the cache).

Answer 1

You can take a different approach to target entity forms:

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Entity\ContentEntityFormInterface;


/**
 * Implements hook_form_alter().
 */
function mymodule_form_alter(array &$form, FormStateInterface $form_state) {

  $form_object = $form_state->getFormObject();
  if (!($form_object instanceof ContentEntityFormInterface)) {
    return;
  }

  $entity = $form_object->getEntity();
  if (!(entity instanceof FooEntityInterface)) {
    return;
  }

  if (!$entity->isNew()) {
    return;
  }

  if ($entity->bundle() !== 'bar') {
    return;
  }

  // alter form
}

Answer 2

This can be done in hook_entity_presave().

function MYMODULE_flagging_presave(FlaggingInterface $flagging) {
  switch ($flagging->getFlagId()) {
    case 'FLAGTYPE':
      $redirect_url = Url::fromRoute('view.VIEW_MACHINE_NAME.VIEW_DISPLAY_ID')->toString();
      $response = new RedirectResponse($redirect_url);
      $response->send();
     break;
   }
 }