Events and Event Listeners

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// src/EventListener/ExceptionListener.php
namespace App\EventListener;

use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\Event\ExceptionEvent;
use Symfony\Component\HttpKernel\Exception\HttpExceptionInterface;

class ExceptionListener
{
    public function __invoke(ExceptionEvent $event): void
    {
        // You get the exception object from the received event
        $exception = $event->getThrowable();
        $message = sprintf(
            'My Error says: %s with code: %s',
            $exception->getMessage(),
            $exception->getCode()
        );

        // Customize your response object to display the exception details
        $response = new Response();
        $response->setContent($message);
        // the exception message can contain unfiltered user input;
        // set the content-type to text to avoid XSS issues
        $response->headers->set('Content-Type', 'text/plain; charset=utf-8');

        // HttpExceptionInterface is a special type of exception that
        // holds status code and header details
        if ($exception instanceof HttpExceptionInterface) {
            $response->setStatusCode($exception->getStatusCode());
            $response->headers->replace($exception->getHeaders());
        } else {
            $response->setStatusCode(Response::HTTP_INTERNAL_SERVER_ERROR);
        }

        // sends the modified response object to the event
        $event->setResponse($response);
    }
}

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// src/EventSubscriber/ExceptionSubscriber.php
namespace App\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\ExceptionEvent;
use Symfony\Component\HttpKernel\KernelEvents;

class ExceptionSubscriber implements EventSubscriberInterface
{
    public static function getSubscribedEvents(): array
    {
        // return the subscribed events, their methods and priorities
        return [
            KernelEvents::EXCEPTION => [
                ['processException', 10],
                ['logException', 0],
                ['notifyException', -10],
            ],
        ];
    }

    public function processException(ExceptionEvent $event)
    {
        // ...
    }

    public function logException(ExceptionEvent $event)
    {
        // ...
    }

    public function notifyException(ExceptionEvent $event)
    {
        // ...
    }
}

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// src/EventListener/RequestListener.php
namespace App\EventListener;

use Symfony\Component\HttpKernel\Event\RequestEvent;

class RequestListener
{
    public function onKernelRequest(RequestEvent $event)
    {
        // The isMainRequest() method was introduced in Symfony 5.3.
        // In previous versions it was called isMasterRequest()
        if (!$event->isMainRequest()) {
            // don't do anything if it's not the main request
            return;
        }

        // ...
    }
}

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// src/EventSubscriber/RequestSubscriber.php
namespace App\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\RequestEvent;

class RequestSubscriber implements EventSubscriberInterface
{
    public static function getSubscribedEvents(): array
    {
        return [
            RequestEvent::class => 'onKernelRequest',
        ];
    }

    public function onKernelRequest(RequestEvent $event)
    {
        // ...
    }
}

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// src/Kernel.php
namespace App;

use App\Event\MyCustomEvent;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\EventDispatcher\DependencyInjection\AddEventAliasesPass;
use Symfony\Component\HttpKernel\Kernel as BaseKernel;

class Kernel extends BaseKernel
{
    protected function build(ContainerBuilder $container)
    {
        $container->addCompilerPass(new AddEventAliasesPass([
            MyCustomEvent::class => 'my_custom_event',
        ]));
    }
}

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class CustomMailer
{
    // ...

    public function send($subject, $message)
    {
        // dispatch an event before the method
        $event = new BeforeSendMailEvent($subject, $message);
        $this->dispatcher->dispatch($event, 'mailer.pre_send');

        // get $subject and $message from the event, they may have been modified
        $subject = $event->getSubject();
        $message = $event->getMessage();

        // the real method implementation is here
        $returnValue = ...;

        // do something after the method
        $event = new AfterSendMailEvent($returnValue);
        $this->dispatcher->dispatch($event, 'mailer.post_send');

        return $event->getReturnValue();
    }
}

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// src/Event/BeforeSendMailEvent.php
namespace App\Event;

use Symfony\Contracts\EventDispatcher\Event;

class BeforeSendMailEvent extends Event
{
    private $subject;
    private $message;

    public function __construct($subject, $message)
    {
        $this->subject = $subject;
        $this->message = $message;
    }

    public function getSubject()
    {
        return $this->subject;
    }

    public function setSubject($subject)
    {
        $this->subject = $subject;
    }

    public function getMessage()
    {
        return $this->message;
    }

    public function setMessage($message)
    {
        $this->message = $message;
    }
}

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// src/Event/AfterSendMailEvent.php
namespace App\Event;

use Symfony\Contracts\EventDispatcher\Event;

class AfterSendMailEvent extends Event
{
    private $returnValue;

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

    public function getReturnValue()
    {
        return $this->returnValue;
    }

    public function setReturnValue($returnValue)
    {
        $this->returnValue = $returnValue;
    }
}

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// src/EventSubscriber/MailPostSendSubscriber.php
namespace App\EventSubscriber;

use App\Event\AfterSendMailEvent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class MailPostSendSubscriber implements EventSubscriberInterface
{
    public function onMailerPostSend(AfterSendMailEvent $event)
    {
        $returnValue = $event->getReturnValue();
        // modify the original $returnValue value

        $event->setReturnValue($returnValue);
    }

    public static function getSubscribedEvents()
    {
        return [
            'mailer.post_send' => 'onMailerPostSend',
        ];
    }
}