Yii Event Dispatcher

PSR-14 compatible event dispatcher provides an ability to dispatch events and listen to events dispatched.

Features

PSR-14 compatible.
Simple and lightweight.
Encourages designing event hierarchy.
Can combine mutliple event listener providers.

General usage

The library consists of two parts: event dispatcher and event listener provider. Provider's job is to register listeners for a certain event type. Dispatcher's job is to take an event, get a listeners for it from a provider and call them sequentially.

$provider = new Yii\EventDispatcher\Provider\Provider();
$dispatcher = new Yii\EventDispatcher\Dispatcher($provider);

// adding some listeners
$provider->attach(function (AfterDocumentProcessed $event) {
    $document = $event->getDocument();
    // do something with document
});

The event dispatching may look like:

class DocumentProcessor
{
    public function process(Document $document)
    {
        // process the document
        $dispatcher->dispatch(new AfterDocumentProcessed($document));
    }
}

Stoppable events

Event could be made stoppable by implementing Psr\EventDispatcher\StoppableEventInterface:

class BusyEvent implements Psr\EventDispatcher\StoppableEventInterface
{
    // ...

    public function isPropagationStopped(): bool
    {
        return true;
    }
}

This way we can ensure that only first event listener will be able to handle the event. Another option is to allow stopping propagation in one of the listeners by providing corresponding event method.

Events hierarchy

Events do not have any name or wildcard matching on purpose. Event class names and class/interface hierarchy and composition could be used to achieve great flexibility:

interface DocumentEvent
{
}

class BeforeDocumentProcessed implements DocumentEvent
{
}

class AfterDocumentProcessed implements DocumentEvent
{
}

With the interface above listening to all document-related events could be done as:

$provider->attach(function (DocumentEvent $event) {
    // log events here
});

Combining multiple listener providers

In case you want to combine multiple listener providers, you can use Aggregate:

$aggregate = new Yii\EventDispatcher\Provider\Aggregate();
$provider1 = new Yii\EventDispatcher\Provider\Provider();
$aggregate->attach($provider1);
$aggregate->attach(new class implements ListenerProviderInterface {
    public function getListenersForEvent(object $event): iterable
    {
        yield function ($event) {
            // handle 
        };
    }
});

$dispatcher = new Yii\EventDispatcher\Dispatcher($aggregate);

Credits

Larry Garfield (@crell) for initial implementation of deriving callable parameter type.