Server events (Omeka\Event) extend from Zend\EventManager\Event. They are triggered from Omeka S's PHP code in a variety of controllers, views and API actions to allow follow-up actions to be done within Omeka S itself or within modules. See the reference page for a full list.

Attaching a listener to an event

The main module class (Module.php) provides a method for easily attaching listeners to events: attachListeners.

Events are triggered based on the name of the event, and the class of the object that triggers it. A typical attachment of a listener in a module looks like:

public function attachListeners(SharedEventManagerInterface $sharedEventManager) 
{
    $sharedEventManager->attach(
        'Omeka\Controller\Admin\Item',
        'view.show.after',
        [$this, 'showSource']
    );
}

The attach method used here takes three arguments:

  1. The class identifier. In this case, it is 'Omeka\Controller\Admin\Item', meaning to only listen for events from the admin-side item controller.

  2. The event identifier. This listener is attaching to the view.show.after event, which is fired within the "show" view.

  3. The callback for the event. Any PHP callback can be given here, including closures, but the [$this, 'methodName'] pattern is common for calling other methods in the same module class. Here, the module will use its showSource method to add content to the view. An Event object is passed to the callback. From that object, inspect the parameters with $event->getParams() or $event->getParam('paramName') to obtain the data you need.

Further details

We use Zend Framework's EventManager component, so many questions can be answered by reading the documentation.