Simple PHP event handling class

FSBOEvent.php

<?php

namespace Events;

class FSBOEvent
{
    /**
     * @var array
     */
    protected static $eventHandlers = [];

    /**
     * @param $eventName
     * @param $payload
     * @return null
     * @usage FSBOEvent::trigger('user.created', $userObject)
     */
    public static function trigger($eventName, $payload)
    {
        if ( ! key_exists($eventName, self::$eventHandlers) ) {
            return null;
        }

        foreach (self::$eventHandlers[$eventName] as $handler) {
            $handler->handle($eventName, $payload);
        }
    }

    /**
     * @param $eventName
     * @param $handler
     * @usage FSBOEvent::on('user.created', Listeners\ExampleUserListener)
     */
    public static function on($eventName, $handler)
    {
        if ( ! key_exists($eventName, self::$eventHandlers) ) {
            self::$eventHandlers[$eventName] = [];
        }
        self::$eventHandlers[$eventName][] = $handler;
    }
}

Examples

class SendNewUserNotification
{
    /**
     * @param $eventName
     * @param null $user
     */
    public function handle($eventName, $user = null)
    {
        var_dump($eventName, $user);
        // @todo send user to gateway
    }
}

FSBOEvent::on('user.registered', new SendNewUserNotification);