Quick Start

Typically, you will compose an EventManager instance in a class.

use Zend\EventManager\EventManagerInterface;
use Zend\EventManager\EventManager;
use Zend\EventManager\EventManagerAwareInterface;

class Foo implements EventManagerAwareInterface
{
    protected $events;

    public function setEventManager(EventManagerInterface $events)
    {
        $events->setIdentifiers([
            __CLASS__,
            get_called_class(),
        ]);
        $this->events = $events;
        return $this;
    }

    public function getEventManager()
    {
        if (null === $this->events) {
            $this->setEventManager(new EventManager());
        }
        return $this->events;
    }
}

The above allows users to access the EventManager instance, or reset it with a new instance; if one does not exist, it will be lazily instantiated on-demand.

The instance property $events is a convention for referring to the EventManager instance.

An EventManager is really only interesting if it triggers some events.

Basic triggering via the trigger() method takes three arguments:

class Foo
{
    // ... assume events definition from above

    public function bar($baz, $bat = null)
    {
        $params = compact('baz', 'bat');
        $this->getEventManager()->trigger(__FUNCTION__, $this, $params);
    }
}

In turn, triggering events is only interesting if something is listening for the event.

Listeners attach to the EventManager, specifying a named event and the callback to notify. The callback receives an Event object, which has accessors for retrieving the event name, target, and parameters. Let's add a listener, and trigger the event.

use Zend\Log\Factory as LogFactory;

$log = LogFactory($someConfig);
$foo = new Foo();
$foo->getEventManager()->attach('bar', function ($e) use ($log) {
    $event  = $e->getName();
    $target = get_class($e->getTarget());
    $params = json_encode($e->getParams());

    $log->info(sprintf(
        '%s called on %s, using params %s',
        $event,
        $target,
        $params
    ));
});

// The following method call:
$foo->bar('baz', 'bat');

// Results in the log message reading:
// bar called on Foo, using params {"baz" : "baz", "bat" : "bat"}"

Note that the second argument to attach() is any valid PHP callable; an anonymous function is shown in the example in order to keep the example self-contained.

However, you could also utilize a valid function name, a functor, a string referencing a static method, or an array callback with a named static method or instance method. Again, any PHP callable is valid.

Sometimes you may want to specify listeners without yet having an object instance of the class composing an EventManager. Zend Framework enables this through the concept of a SharedEventManager.

Simply put, you can inject individual EventManager instances with a well-known SharedEventManager, and the EventManager instance will query it for additional listeners.

Listeners attach to a SharedEventManager in roughly the same way they do to normal event managers; the call to attach is identical to the EventManager, but expects an additional parameter at the beginning: a named instance.

Remember the example of composing an EventManager, how we passed it an array containing __CLASS__ and get_class($this)? Those values are then used to identify the event manager instance, and pull listeners registered with one of those identifiers from the SharedEventManager.

As an example, assuming we have a SharedEventManager instance that we know has been injected in our EventManager instances (for instance, via dependency injection), we could change the above example to attach via the shared collection:

use Zend\Log\Factory as LogFactory;

// Assume $sharedEvents is a Zend\EventManager\SharedEventManager instance

$log = LogFactory($someConfig);
$sharedEvents->attach('Foo', 'bar', function ($e) use ($log) {
    $event  = $e->getName();
    $target = get_class($e->getTarget());
    $params = json_encode($e->getParams());

    $log->info(sprintf(
        '%s called on %s, using params %s',
        $event,
        $target,
        $params
    ));
});

// Later, instantiate Foo:
$foo = new Foo();
$foo->setEventManager(new EventManager($sharedEvents, []));

// And we can still trigger the above event:
$foo->bar('baz', 'bat');
// results in log message:
// bar called on Foo, using params {"baz" : "baz", "bat" : "bat"}"

The EventManager also provides the ability to detach listeners, short-circuit execution of an event either from within a listener or by testing return values of listeners, test and loop through the results returned by listeners, prioritize listeners, and more. Many of these features are detailed in the examples.