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Listening to Core events

Description

When you interact with the Public API, and with the content Repository in particular, Signals may be sent out, allowing you to react on actions triggered by the Repository. Those signals can be received by dedicated services called Slots.

Note

To learn more about SignalSlot in eZ Platform, please refer to the dedicated documentation page.

Signals reference

This recipe will describe how to register a Slot for a dedicated Signal.

Solution

Registering a Slot for a given Signal

As described in the SignalSlot documentation, a Slot is roughly like an event listener and must extend eZ\Publish\Core\SignalSlot\Slot.

A typical implementation is the following:

// OnPublishSlot
namespace Acme\TestBundle\Slot;
 
use eZ\Publish\Core\SignalSlot\Slot as BaseSlot;
use eZ\Publish\Core\SignalSlot\Signal;
use eZ\Publish\API\Repository\ContentService;

class OnPublishSlot extends BaseSlot
{
    /**
     * @var \eZ\Publish\API\Repository\ContentService
     */
    private $contentService;

    public function __construct( ContentService $contentService )
    {
        $this->contentService = $contentService;
    }

    public function receive( Signal $signal )
    {
        if ( !$signal instanceof Signal\ContentService\PublishVersionSignal )
        {
            return;
        }

        // Load published content
        $content = $this->contentService->loadContent( $signal->contentId, null, $signal->versionNo );
        // Do stuff with it...
    }
}

OnPublishSlot now needs to be registered as a service in the ServiceContainer and identified as a valid Slot:

# services.yml (in your bundle)
parameters:
    my.onpublish_slot.class: Acme\TestBundle\Slot\OnPublishSlot
 
services:
    my.onpublish_slot:
        class: %my.onpublish_slot.class%
        arguments: [@ezpublish.api.service.content]
        tags:
            - { name: ezpublish.api.slot, signal: ContentService\PublishVersionSignal }

Service tag ezpublish.api.slot identifies your service as a valid Slot. The signal part (mandatory) says that this slot is listening to ContentService\PublishVersionSignal (shortcut for \eZ\Publish\Core\SignalSlot\Signal\ContentService\PublishVersionSignal).

Note

Internal signals emitted by Repository services are always relative to eZ\Publish\Core\SignalSlot\Signal namespace.

Hence ContentService\PublishVersionSignal means eZ\Publish\Core\SignalSlot\Signal\ContentService\PublishVersionSignal.

Tip

You can register a slot for any kind of signal by setting signal to * in the service tag.

Using a basic Symfony event listener

eZ Platform comes with a generic slot that converts signals (including ones defined by user code) to regular event objects and exposes them via the EventDispatcher. This makes it possible to implement a simple event listener/subscriber if you're more comfortable with this approach.

All you need to do is to implement an event listener or subscriber and register it.

Example

This very simple example will just log the received signal.

# services.yml (in your bundle)
parameters:
    my.signal_listener.class: Acme\TestBundle\EventListener\SignalListener
 
services:
    my.signal_listener:
        class: %my.signal_listener.class%
        arguments: [@logger]
        tags:
            - { name: kernel.event_subscriber }
<?php
namespace Acme\TestBundle\EventListener;

use eZ\Publish\Core\MVC\Symfony\Event\SignalEvent;
use eZ\Publish\Core\MVC\Symfony\MVCEvents;
use Psr\Log\LoggerInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class SignalListener implements EventSubscriberInterface
{
    /**
     * @var \Psr\Log\LoggerInterface
     */
    private $logger;

    public function __construct( LoggerInterface $logger )
    {
        $this->logger = $logger;
    }

    public function onAPISignal( SignalEvent $event )
    {
        $signal = $event->getSignal();
        // You may want to check the signal type here to react accordingly
        $this->logger->debug( 'Received Signal: ' . print_r( $signal, true ) );
    }

    public static function getSubscribedEvents()
    {
        return array(
            MVCEvents::API_SIGNAL => 'onAPISignal'
        );
    }
}
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