class EventsExampleSubscriber in Examples for Developers 8

Subscribe to IncidentEvents::NEW_REPORT events and react to new reports.

In this example we subscribe to all IncidentEvents::NEW_REPORT events and point to two different methods to execute when the event is triggered. In each method we have some custom logic that determines if we want to react to the event by examining the event object, and the displaying a message to the user indicating whether or not that method reacted to the event.

By convention, classes subscribing to an event live in the Drupal/{module_name}/EventSubscriber namespace.

Hierarchy

• class \Drupal\events_example\EventSubscriber\EventsExampleSubscriber implements \Symfony\Component\EventDispatcher\EventSubscriberInterface uses MessengerTrait, StringTranslationTrait

Related topics

Example: Events

Demonstrates subscribing to, and dispatching, events.

1 file declares its use of EventsExampleSubscriber

EventsExampleServiceTest.php in events_example/tests/src/Kernel/EventsExampleServiceTest.php

1 string reference to 'EventsExampleSubscriber'

events_example.services.yml in events_example/events_example.services.yml

events_example/events_example.services.yml

1 service uses EventsExampleSubscriber

events_example_subscriber in events_example/events_example.services.yml

Drupal\events_example\EventSubscriber\EventsExampleSubscriber

File

events_example/src/EventSubscriber/EventsExampleSubscriber.php, line 25

Namespace

Drupal\events_example\EventSubscriber

class EventsExampleSubscriber implements EventSubscriberInterface {
  use StringTranslationTrait;
  use MessengerTrait;

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {

    // Return an array of events that you want to subscribe to mapped to the
    // method on this class that you would like called whenever the event is
    // triggered. A single class can subscribe to any number of events. For
    // organization purposes it's a good idea to create a new class for each
    // unique task/concept rather than just creating a catch-all class for all
    // event subscriptions.
    //
    // See EventSubscriberInterface::getSubscribedEvents() for an explanation
    // of the array's format.
    //
    // The array key is the name of the event your want to subscribe to. Best
    // practice is to use the constant that represents the event as defined by
    // the code responsible for dispatching the event. This way, if, for
    // example, the string name of an event changes your code will continue to
    // work. You can get a list of event constants for all events triggered by
    // core here:
    // https://api.drupal.org/api/drupal/core%21core.api.php/group/events/8.2.x.
    //
    // Since any module can define and trigger new events there may be
    // additional events available in your application. Look for classes with
    // the special @Event docblock indicator to discover other events.
    //
    // For each event key define an array of arrays composed of the method names
    // to call and optional priorities. The method name here refers to a method
    // on this class to call whenever the event is triggered.
    $events[IncidentEvents::NEW_REPORT][] = [
      'notifyMario',
    ];

    // Subscribers can optionally set a priority. If more than one subscriber is
    // listening to an event when it is triggered they will be executed in order
    // of priority. If no priority is set the default is 0.
    $events[IncidentEvents::NEW_REPORT][] = [
      'notifyBatman',
      -100,
    ];

    // We'll set an event listener with a very low priority to catch incident
    // types not yet defined. In practice, this will be the 'cat' incident.
    $events[IncidentEvents::NEW_REPORT][] = [
      'notifyDefault',
      -255,
    ];
    return $events;
  }

  /**
   * If this incident is about a missing princess notify Mario.
   *
   * Per our configuration above, this method is called whenever the
   * IncidentEvents::NEW_REPORT event is dispatched. This method is where you
   * place any custom logic that you want to perform when the specific event is
   * triggered.
   *
   * These responder methods receive an event object as their argument. The
   * event object is usually, but not always, specific to the event being
   * triggered and contains data about application state and configuration
   * relative to what was happening when the event was triggered.
   *
   * For example, when responding to an event triggered by saving a
   * configuration change you'll get an event object that contains the relevant
   * configuration object.
   *
   * @param \Drupal\events_example\Event\IncidentReportEvent $event
   *   The event object containing the incident report.
   */
  public function notifyMario(IncidentReportEvent $event) {

    // You can use the event object to access information about the event passed
    // along by the event dispatcher.
    if ($event
      ->getType() == 'stolen_princess') {
      $this
        ->messenger()
        ->addStatus($this
        ->t('Mario has been alerted. Thank you. This message was set by an event subscriber. See @method()', [
        '@method' => __METHOD__,
      ]));

      // Optionally use the event object to stop propagation.
      // If there are other subscribers that have not been called yet this will
      // cause them to be skipped.
      $event
        ->stopPropagation();
    }
  }

  /**
   * Let Batman know about any events involving the Joker.
   *
   * @param \Drupal\events_example\Event\IncidentReportEvent $event
   *   The event object containing the incident report.
   */
  public function notifyBatman(IncidentReportEvent $event) {
    if ($event
      ->getType() == 'joker') {
      $this
        ->messenger()
        ->addStatus($this
        ->t('Batman has been alerted. Thank you. This message was set by an event subscriber. See @method()', [
        '@method' => __METHOD__,
      ]));
      $event
        ->stopPropagation();
    }
  }

  /**
   * Handle incidents not handled by the other handlers.
   *
   * @param \Drupal\events_example\Event\IncidentReportEvent $event
   *   The event object containing the incident report.
   */
  public function notifyDefault(IncidentReportEvent $event) {
    $this
      ->messenger()
      ->addStatus($this
      ->t('Thank you for reporting this incident. This message was set by an event subscriber. See @method()', [
      '@method' => __METHOD__,
    ]));
    $event
      ->stopPropagation();
  }

}

Members

Name	Modifiers	Type	Description	Overrides
EventsExampleSubscriber::getSubscribedEvents	public static	function	Returns an array of event names this subscriber wants to listen to.
EventsExampleSubscriber::notifyBatman	public	function	Let Batman know about any events involving the Joker.
EventsExampleSubscriber::notifyDefault	public	function	Handle incidents not handled by the other handlers.
EventsExampleSubscriber::notifyMario	public	function	If this incident is about a missing princess notify Mario.
MessengerTrait::$messenger	protected	property	The messenger.	29
MessengerTrait::messenger	public	function	Gets the messenger.	29
MessengerTrait::setMessenger	public	function	Sets the messenger.
StringTranslationTrait::$stringTranslation	protected	property	The string translation service.	1
StringTranslationTrait::formatPlural	protected	function	Formats a string containing a count of items.
StringTranslationTrait::getNumberOfPlurals	protected	function	Returns the number of plurals supported by a given language.
StringTranslationTrait::getStringTranslation	protected	function	Gets the string translation service.
StringTranslationTrait::setStringTranslation	public	function	Sets the string translation service to use.	2
StringTranslationTrait::t	protected	function	Translates a string to the current language or to a given language.