adjaya-dev / event-dispatcher

PSR-14 compatible event dispatcher that's easy to use

Jasny Event Dispatcher

A PSR-14 compatible event dispatcher that's easy to use.

Event dispatching is a common and well-tested mechanism to allow developers to inject logic into an application easily and consistently.

The PSR only requires determining events based on their class name, any other method is optional. Libraries should only depend on the specification and not on the implementation, therefore each event type must have it's own class.

Installation

composer require jasny/event-dispatcher

Usage

1. Define your own event classes

namespace App\Event;

/**
 * Base class for all events in this application.
 */
abstract class Base
{
    /** @var object */
    protected $emitter;

    /** @var mixed */
    protected $payload;

    public function __construct(object $emitter, $payload = null)
    {
        $this->emitter = $emitter;
        $this->payload = $payload;
    }
    
    public function getEmitter(): object
    {
        return $this->subject;
    }

    public function setPayload($payload): void
    {
        $this->payload = $payload;
    }

    public function getPayload()
    {
        return $this->payload;
    }
}

/**
 * Called before an entity is saved to the database.
 */
class BeforeSave extends Base
{}

/**
 * Called when an entity is casted to json.
 */
class ToJson extends Base
{} 

2. Create listeners

use App\Event;
use Jasny\EventDispatcher\EventDispatcher;
use Jasny\EventDispatcher\ListenerProvider;

$listener = (new ListenerProvider)
    ->withListener(function(Event\BeforeSave $event): void {
        $entity = $event->getEmitter();
        $payload = $event->getPayload();
        
        $payload['bio'] = $payload['bio'] ?? ($entity->name . " just arrived");
        $event->setPayload($payload);
    })
    ->withListener(function(Event\ToJson $event): void {
        $payload = $event->getPayload();
        
        unset($payload['password']);
        $event->setPayload($payload);
    });

The provider will use the type hint of the first argument of the lister to determine if the listener applies to the given event.

Listeners are executed in the order they're registered to the provider. It's not possible to prepend existing listeners.

3. Create the dispatcher

$dispatcher = new EventDispatcher($listener);

4. Dispatch an event

Typically a subject will hold its own dispatcher and trigger events.

use App\Event;
use Jasny\EventDispatcher\EventDispatcher;

class Foo implements JsonSerializable
{
    /**
     * @var EventDispatcher
     */
    protected $eventDispatcher;

    // ...
    
    public function jsonSerialize()
    {
        $payload = get_object_vars($this);
    
        return $this->eventDispatcher->dispatch(new Event\ToJson($this, $payload));
    }
}

Add listener

ListenerProvider and EventDispatcher are immutable services. Methods withListener and withListenerProvider resp will create a modified copy of each service.

use App\Event;

$newListener = $dispatcher->getListener()
    ->off(function(Event\BeforeSave $event): void {
        $payload = $event->getPayload();
       
        $payload['bio'] = strtr($payload['bio'], $payload['email'], '***@***.***');
        $event->setPayload($payload);
    });

$newDispatcher = $dispatcher->withListenerProvider($newListener);

Stoppable events

The event must implement the StoppableEventInterface of PSR-14.

namespace App\Event;

use Psr\EventDispatcher\StoppableEventInterface;

/**
 * Called before an entity is saved to the database.
 */
class BeforeSave implememnts StoppableEventInterface
{
    // ...

    public function stopPropagation(): void
    {
        $this->propagationStopped = true;
    }

    public function isPropagationStopped(): bool
    {
        return $this->propagationStopped;
    }
}

use App\Event;
use Jasny\EventDispatcher\EventDispatcher;
use Jasny\EventDispatcher\ListenerProvider;

$listener = (new ListenerProvider)
    ->on(function(Event\BeforeSave $event): void {
        $entity = $event->getEmitter();
        
        if (!$entity->isReady()) {
            $event->stopPropagation();
        }
    });
    
$dispatcher = new EventDispatcher($listener);

Listener namespace

Listeners may be registered to the provider under a namespace.

use App\Event;
use Jasny\EventDispatcher\EventDispatcher;
use Jasny\EventDispatcher\ListenerProvider;

$listener = (new ListenerProvider)
    ->withListenerInNs('censor', function(Event\BeforeSave $event): void {
        $payload = $event->getPayload();
        
        $payload['bio'] = strtr($payload['bio'], $payload['email'], '***@***.***');
        $event->setPayload($payload);
    });
    ->withListenerInNs('censor.json', function(Event $event): void {
        $payload = $event->getPayload();
        
        unset($payload['password']);
        $event->setPayload($payload);
    });

This can be used to remove all listeners within the namespace and all subnamespaces.

$newListeners = $dispatcher->getListenerProvider()->withoutNs('censor');

This example removes both the listener in the censor and censor.json namespace.

Namespace wildcard

You may use a wildcard to specify all subnamespaces regardless of the parent

$newListeners = $dispatcher->getListenerProvider()->withoutNs('*.json');

This example removes the listener in the censor.json namespace.