Semperton Events

A minimal, PSR-14 compilant event library.

Installation

Just use Composer:

composer require semperton/events

Events requires PHP 7.4+

Adding listeners

Listeners are added with an event class or interface name, a listener callback and an optional priority value (default is 0, negative values allowed). The listener callback can be any PHP callable and should accept only one argument - the event object.

use Semperton\Events\ListenerProvider;

interface EventInterface{}
final class TestEvent implements EventInterface
{
	public $message = '';
}

$provider = new ListenerProvider();

$provider->addListener(TestEvent::class, function (TestEvent $event) {
	$event->message .= ' World';
});

$provider->addListener(EventInterface::class, function (EventInterface $event) {
	$event->message = 'Hello';
}, -1); // gets called first, because of higher priority (negatives allowed)

If you register a listener with an interface name, that listener will also be triggered if the dispatched event implements said interface.

Removing listeners

Remove listeners with the removeListener() method. Event name, listener and priority must match.

$myListener = function (TestEvent $event) {};

$provider->addListener(TestEvent::class, $myListener, 7);
$provider->removeListener(TestEvent::class, $myListener, 7); // priority must match too

Dispatching

All you need is a ListenerProvider (collection of event listeners) and an EventDispatcher.

use Semperton\Events\EventDispatcher;

// using the previously created ListenerProvider
$dispatcher = new EventDispatcher($provider);

$event = new TestEvent();

/** @var TestEvent */
$dispatchedEvent = $dispatcher->dispatch($event);

$dispatchedEvent === $event; // true
$dispatchedEvent->message; // 'Hello World'

DelegateListener example

If you want to call service methods in response to events, you may use a callable to resolve your services, etc. For this purpose a DelegateListener can be helpful:

$resolver = static function (string $class): object {
	return new $class();
};

$listener = new DelegateListener($resolver, Service::class, 'method');

Or use the get function of a PSR-11 Container as a resolver:

// $container is a Psr\Container\ContainerInterface
$listener = new DelegateListener([$container, 'get'], Service::class, 'method');
$provider->addListener(TestEvent::class, $listener);