exercise_05-events.md

Drupal 8 Backend Training

Exercise 5:

Events

A Drupal 8 Event is very similar to hooks in both Drupal 7 and Drupal 8. It's basically a method of allowing developers to respond to certain occurences within the Drupal execution flow. In this exercise we'll demonstrate the concept of events by hiding the route we created in Exercise 3, but first a disclaimer: This is a purely didactic example, it is only intended to demonstrate how Events are used and is not a good way to handle route accessibility.

1. To start let's use our trusty Drupal Console to generate an Event listener:

   lando drupal generate:event:subscriber

    Enter the module name [admin_toolbar]:
    > example
   
    Enter the service name [example.default]:
    > example.hide_route
   
    Enter the class name [DefaultSubscriber]:
    > HideRouteSubscriber
   
   
   Type the event name or use keyup or keydown.
   This is optional, press enter to continue
   
    Enter event name []:
    > kernel.request
   
    Enter the callback function name to handle event [kernel_request]:
    > handleRequest
   
    Enter event name []:
    >
   
    Do you want to load services from the container? (yes/no) [no]:
    > yes
   
   
   Type the service name or use keyup or keydown.
   This is optional, press enter to continue
   
    Enter your service []:
    > current_route_match
    Enter your service []:
    >
   
    Do you want proceed with the operation? (yes/no) [yes]:
    >

2. Open /modules/custom/example/example.services.yml and notice that there's a new service with the service name specified above, and with a special tag specifiying that it's an event subscriber.

3. Go to your dev site and visit /example/site-name and verify that it's working.

4. Edit /modules/custom/example/src/EventSubscriber/HideRouteSubscriber.php and edit the handleRequest method to mirror the following:

   public function handleRequest(Event $event) {
     if ($this->currentRouteMatch->getRouteName() === 'example.example_controller_getSiteName') {
       throw new \Symfony\Component\HttpKernel\Exception\NotFoundHttpException();
     }
   }

5. Refresh the page and verify that you now get a 404 error.

Next Exercise (#6 Module Settings)