1. 8.3.x core/core.api.php events
  2. 8.0.x core/core.api.php events
  3. 8.1.x core/core.api.php events
  4. 8.2.x core/core.api.php events
  5. 8.4.x core/core.api.php events

Overview of event dispatch and subscribing

Introduction and terminology

Events are part of the Symfony framework: they allow for different components of the system to interact and communicate with each other. Each event has a unique string name. One system component dispatches the event at an appropriate time; many events are dispatched by Drupal core and the Symfony framework in every request. Other system components can register as event subscribers; when an event is dispatched, a method is called on each registered subscriber, allowing each one to react. For more on the general concept of events, see http://symfony.com/doc/current/components/event_dispatcher/introduction....

Dispatching events

To dispatch an event, call the \Symfony\Component\EventDispatcher\EventDispatcherInterface::dispatch() method on the 'event_dispatcher' service (see the Services topic for more information about how to interact with services). The first argument is the unique event name, which you should normally define as a constant in a separate static class (see \Symfony\Component\HttpKernel\KernelEvents and \Drupal\Core\Config\ConfigEvents for examples). The second argument is a \Symfony\Component\EventDispatcher\Event object; normally you will need to extend this class, so that your event class can provide data to the event subscribers.

Registering event subscribers

Here are the steps to register an event subscriber:

  • Define a service in your module, tagged with 'event_subscriber' (see the Services topic for instructions).
  • Define a class for your subscriber service that implements \Symfony\Component\EventDispatcher\EventSubscriberInterface
  • In your class, the getSubscribedEvents method returns a list of the events this class is subscribed to, and which methods on the class should be called for each one. Example:

  public static function getSubscribedEvents() {
    // Subscribe to kernel terminate with priority 100.
    $events[KernelEvents::TERMINATE][] = array('onTerminate', 100);
    // Subscribe to kernel request with default priority of 0.
    $events[KernelEvents::REQUEST][] = array('onRequest');
    return $events;
  }
  
  • Write the methods that respond to the events; each one receives the event object provided in the dispatch as its one argument. In the above example, you would need to write onTerminate() and onRequest() methods.

Note that in your getSubscribedEvents() method, you can optionally set the priority of your event subscriber (see terminate example above). Event subscribers with higher priority numbers get executed first; the default priority is zero. If two event subscribers for the same event have the same priority, the one defined in a module with a lower module weight will fire first. Subscribers defined in the same services file are fired in definition order. If order matters defining a priority is strongly advised instead of relying on these two tie breaker rules as they might change in a minor release.

File

core/core.api.php, line 2515
Documentation landing page and topics, plus core library hooks.

Constants

Namesort descending Location Description
ConfigEvents::COLLECTION_INFO core/lib/Drupal/Core/Config/ConfigEvents.php Name of event fired to collect information on all config collections.
ConfigEvents::DELETE core/lib/Drupal/Core/Config/ConfigEvents.php Name of the event fired when deleting a configuration object.
ConfigEvents::IMPORT core/lib/Drupal/Core/Config/ConfigEvents.php Name of the event fired when importing configuration to target storage.
ConfigEvents::IMPORT_VALIDATE core/lib/Drupal/Core/Config/ConfigEvents.php Name of the event fired when validating imported configuration.
ConfigEvents::RENAME core/lib/Drupal/Core/Config/ConfigEvents.php Name of the event fired when renaming a configuration object.
ConfigEvents::SAVE core/lib/Drupal/Core/Config/ConfigEvents.php Name of the event fired when saving a configuration object.
ConsoleEvents::COMMAND vendor/symfony/console/ConsoleEvents.php The COMMAND event allows you to attach listeners before any command is executed by the console. It also allows you to modify the command, input and output before they are handled to the command.
ConsoleEvents::EXCEPTION vendor/symfony/console/ConsoleEvents.php The EXCEPTION event occurs when an uncaught exception appears.
ConsoleEvents::TERMINATE vendor/symfony/console/ConsoleEvents.php The TERMINATE event allows you to attach listeners after a command is executed by the console.
EntityTypeEvents::CREATE core/lib/Drupal/Core/Entity/EntityTypeEvents.php The name of the event triggered when a new entity type is created.
EntityTypeEvents::DELETE core/lib/Drupal/Core/Entity/EntityTypeEvents.php The name of the event triggered when an existing entity type is deleted.
EntityTypeEvents::UPDATE core/lib/Drupal/Core/Entity/EntityTypeEvents.php The name of the event triggered when an existing entity type is updated.
FieldStorageDefinitionEvents::CREATE core/lib/Drupal/Core/Field/FieldStorageDefinitionEvents.php Name of the event triggered for field storage definition creation.
FieldStorageDefinitionEvents::DELETE core/lib/Drupal/Core/Field/FieldStorageDefinitionEvents.php Name of the event triggered for field storage definition deletion.
FieldStorageDefinitionEvents::UPDATE core/lib/Drupal/Core/Field/FieldStorageDefinitionEvents.php Name of the event triggered for field storage definition update.
KernelEvents::CONTROLLER vendor/symfony/http-kernel/KernelEvents.php The CONTROLLER event occurs once a controller was found for handling a request.
KernelEvents::EXCEPTION vendor/symfony/http-kernel/KernelEvents.php The EXCEPTION event occurs when an uncaught exception appears.
KernelEvents::FINISH_REQUEST vendor/symfony/http-kernel/KernelEvents.php The FINISH_REQUEST event occurs when a response was generated for a request.
KernelEvents::REQUEST vendor/symfony/http-kernel/KernelEvents.php The REQUEST event occurs at the very beginning of request dispatching.
KernelEvents::RESPONSE vendor/symfony/http-kernel/KernelEvents.php The RESPONSE event occurs once a response was created for replying to a request.
KernelEvents::TERMINATE vendor/symfony/http-kernel/KernelEvents.php The TERMINATE event occurs once a response was sent.
KernelEvents::VIEW vendor/symfony/http-kernel/KernelEvents.php The VIEW event occurs when the return value of a controller is not a Response instance.
LanguageConfigOverrideEvents::DELETE_OVERRIDE core/modules/language/src/Config/LanguageConfigOverrideEvents.php The name of the event fired when deleting the configuration override.
LanguageConfigOverrideEvents::SAVE_OVERRIDE core/modules/language/src/Config/LanguageConfigOverrideEvents.php The name of the event fired when saving the configuration override.
LocaleEvents::SAVE_TRANSLATION core/modules/locale/src/LocaleEvents.php The name of the event fired when saving a translated string.
MigrateEvents::IDMAP_MESSAGE core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired when saving a message to the idmap.
MigrateEvents::MAP_DELETE core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired when removing an entry from a migration's map.
MigrateEvents::MAP_SAVE core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired when saving to a migration's map.
MigrateEvents::POST_IMPORT core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired when finishing a migration import operation.
MigrateEvents::POST_ROLLBACK core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired when finishing a migration rollback operation.
MigrateEvents::POST_ROW_DELETE core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired just after a single item has been deleted.
MigrateEvents::POST_ROW_SAVE core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired just after a single item has been imported.
MigrateEvents::PRE_IMPORT core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired when beginning a migration import operation.
MigrateEvents::PRE_ROLLBACK core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired when beginning a migration rollback operation.
MigrateEvents::PRE_ROW_DELETE core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired when about to delete a single item.
MigrateEvents::PRE_ROW_SAVE core/modules/migrate/src/Event/MigrateEvents.php Name of the event fired when about to import a single item.
RenderEvents::SELECT_PAGE_DISPLAY_VARIANT core/lib/Drupal/Core/Render/RenderEvents.php Name of the event when selecting a page display variant to use.
RoutingEvents::ALTER core/lib/Drupal/Core/Routing/RoutingEvents.php Name of the event fired during route collection to allow changes to routes.
RoutingEvents::DYNAMIC core/lib/Drupal/Core/Routing/RoutingEvents.php Name of the event fired during route collection to allow new routes.
RoutingEvents::FINISHED core/lib/Drupal/Core/Routing/RoutingEvents.php Name of the event fired to indicate route building has ended.