Event Dispatcher

based on Symfony 2.8

Sommaire

Problem
Design Pattern
How to use it
1. Events
2. Dispatcher
3. Listeners
Dig into Symfony

Problem

In order to have a good object oriented design we have to create lots of classes interacting one with each other. If certain principles are not applied the final framework will end in a total mess where each object relies on many other objects in order to run. In order to avoid tight coupled frameworks, we need a mechanism to facilitate the interaction between objects in a manner in that objects are not aware of the existence of other objects.

Source: oodesign.com/mediator-pattern.html

Design Pattern

Mediator Pattern

Communication between objects is encapsulated with a mediator object. Objects no longer communicate directly with each other, but instead communicate through the mediator. This reduces the dependencies between communicating objects, thereby lowering the coupling.

Source: en.wikipedia.org/wiki/Mediator_pattern

Mediator

Without

With

Symfony EventDispatcher

{
    "require": {
        "symfony/event-dispatcher" : "^2.7"
    }
}

$ composer require symfony/event-dispatcher

{
    "require": {
        "php": ">=5.3.9"
    },
    "require-dev": {
        "symfony/phpunit-bridge":       "~2.7",
        "symfony/dependency-injection": "~2.6",
        "symfony/expression-language":  "~2.6",
        "symfony/config":               "~2.0,>=2.0.5",
        "symfony/stopwatch":            "~2.3",
        "psr/log":                      "~1.0"
    },
    "suggest": {
        "symfony/dependency-injection": "",
        "symfony/http-kernel": ""
    }
}

Install

1. Events

2. Dispatcher

3. Listeners

Event Names

have a unique name

kernel.request

kernel.response

form.bind

form.post_set_data

console.command

console.exception

Event Names

<?php

namespace Symfony\Component\HttpKernel;

final class KernelEvents
{
    /**
     * The REQUEST event occurs at the very beginning of request
     * dispatching.
     *
     * This event allows you to create a response for a request before any
     * other code in the framework is executed. The event listener method
     * receives a Symfony\Component\HttpKernel\Event\GetResponseEvent
     * instance.
     */
    const REQUEST = 'kernel.request';

    /**
     * The EXCEPTION event occurs when an uncaught exception appears.
     *
     * This event allows you to create a response for a thrown exception or
     * to modify the thrown exception. The event listener method receives
     * a Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent
     * instance.
     */
    const EXCEPTION = 'kernel.exception';

    // ...
}

Event Objects

Event
- propagationStopped: bool = false
+ isPropagationStopped(): bool + stopPropagation()

Instances of

Symfony\Component\EventDispatcher\Event

Event Objects

Symfony\Component\EventDispatcher\GenericEvent

GenericEvent
- subject : mixed - arguments : array
+ getSubject(): mixed + getArgument(string): mixed + setArgument(string, mixed): mixed + getArguments(): mixed + setArguments(array): mixed + hasArgument(string): bool

Event

\ArrayAccess

\IteratorAggregate

Dispatcher

Use a Single Instance

$dispatcher = $this->getContainer()->get('event_dispatcher');

Dispatcher

Symfony\Component\EventDispatcher\EventDispatcherInterface

+ dispatch(string, Event $event = null): Event + addListeners(string, callable, int = 0) + addSubscriber(EventSubscriberInterface) + removeListener(string, callable) + removeSubscriber(EventSubscriberInterface) + getListeners(string = null) + hasListeners(string = null)

Dispatcher

$dispatcher = $this->getContainer()->get('event_dispatcher');

// event name only
$dispatcher->dispatch('store.order');


// with event object
$event = new StoreOrderEvent($order);
$dispatcher->dispatch(StoreEvents::STORE_ORDER, $event);

Dispatcher Extras

Symfony\Component\EventDispatcher\

ImmutableEventDispatcher

Symfony\Component\EventDispatcher\

ContainerAwareEventDispatcher

Symfony\Component\EventDispatcher\

Debug\TracableEventDispatcher

Listeners

use Symfony\Component\EventDispatcher\Event;
use Symfony\Component\EventDispatcher\EventDispatcher;

$dispatcher = new EventDispatcher();

$listener = function (Event $event) {
    echo 'A';
};

$dispatcher->addListener(
    'example',     // Event name to listen
    $listener,     // A PHP callable (aka callback)
    $priority = 0  // Priority 
);

Reminder: PHP Callable

function my_callback_function() {
    echo 'hello world!';
}

class MyClass {
    static function myCallbackMethod() {
        echo 'Hello World!';
    }
}

// Type 1: Simple callback
call_user_func('my_callback_function'); 

// Type 2: Static class method call
call_user_func(array('MyClass', 'myCallbackMethod')); 

// Type 3: Object method call
$obj = new MyClass();
call_user_func(array($obj, 'myCallbackMethod'));

// Type 4: Static class method call (As of PHP 5.2.3)
call_user_func('MyClass::myCallbackMethod');

Source: php.net/manual/en/language.types.callable.php

// Type 5: Relative static class method call (As of PHP 5.3.0)
class A {
    public static function who() {
        echo "A\n";
    }
}

class B extends A {
    public static function who() {
        echo "B\n";
    }
}

call_user_func(array('B', 'parent::who')); // A

// Type 6: Objects implementing __invoke can be used as callables (since PHP 5.3)
class C {
    public function __invoke($name) {
        echo 'Hello ', $name, "\n";
    }
}

$c = new C();
call_user_func($c, 'PHP!');

// Anonymous functions
$listener = function (Event $e) {
    echo "C\n";
}

$dispatcher->addListener('example', $listener);

Subscribers

Symfony\Component\EventDispatcher\EventSubscriberInterface

+ getSubscribedEvents(): array

Subscribers

use Symfony\Component\EventDispatcher\Event;
use Symfony\Component\EventDispatcher\GenericEvent;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\EventDispatcher\EventDispatcher;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class EventSubscriber implements EventSubscriberInterface
{
    public static function getSubscribedEvents()
    {
        return [
            'kernel.request' => 'onKernelRequest',
            'user.update' => ['onUserUpdate', 5],
            'blog_post.saved' => [
                ['updateRss', 10],
                ['sendEmails', 5],
            ]
        ];
    }

    public function onKernelRequest(GetResponseEvent $event) { /** ... */ }
    public function onUserUpdate(GenericEvent $event) { /** ... */ }
    public function updateRss(Event $event) { /** ... */ }
    public function sendEmails(Event $event) { /** ... */ }
}

$dispatcher = new EventDispatcher();

$subscriber = new EventSubscriber();
$dispatcher->addSubscriber($subscriber);

Stop propagation

use Symfony\Component\EventDispatcher\Event;
use Symfony\Component\EventDispatcher\EventDispatcher;

$dispatcher = new EventDispatcher();

$dispatcher->addListener('example', function (Event $event) {
    echo 'A';
    $event->stopPropagation();
});
$dispatcher->addListener('example', function (Event $event) {
    echo 'B';
});

$dispatcher->dispatch('example'); // output : A

Dig in Symfony

Workflow
List of events
Service definition
Tools

Workflow

List of Events

Kernel

Console

Form

Security

Doctrine

Kernel

Name	KernelEvents Constant	Event Object
kernel.request	KernelEvents::REQUEST	GetResponseEvent
kernel.controller	KernelEvents::CONTROLLER	FilterControllerEvent
kernel.view	KernelEvents::VIEW	GetResponseForControllerResultEvent
kernel.response	KernelEvents::RESPONSE	FilterResponseEvent
kernel.finish_request	KernelEvents::FINISH_REQUEST	FinishRequestEvent
kernel.terminate	KernelEvents::TERMINATE	PostResponseEvent
kernel.exception	KernelEvents::EXCEPTION	GetResponseForExceptionEvent

Symfony\Component\HttpKernel\KernelEvents

Console

Name	ConsoleEvents Constant	Event Object
console.command	ConsoleEvents::COMMAND	ConsoleCommandEvent
console.terminate	ConsoleEvents::TERMINATE	ConsoleTerminateEvent
console.exception	ConsoleEvents::EXCEPTION	ConsoleExceptionEvent

Symfony\Component\Console\ConsoleEvents

Form

Name	FormEvents Constant	Event Object
form.pre_bind	FormEvents::PRE_SUBMIT	FormEvent
form.bind	FormEvents::SUBMIT	FormEvent
form.post_bind	FormEvents::POST_SUBMIT	FormEvent
form.pre_set_data	FormEvents::PRE_SET_DATA	FormEvent
form.post_set_data	FormEvents::POST_SET_DATA	FormEvent

Symfony\Component\Form\FormEvents

Security

Name	SecurityEvents Constant	Event Object
security.interactive_login	SecurityEvents::INTERACTIVE_LOGIN	InteractiveLoginEvent
security.switch_user	SecurityEvents::SWITCH_USER	SwitchUserEvent

Symfony\Component\Security\Http\SecurityEvents

Name	AuthenticationEvents Constant	Event Object
security.authentication.success	AuthenticationEvents::AUTHENTICATION_SUCCESS	AuthenticationEvent
security.authentication.failure	AuthenticationEvents::AUTHENTICATION_FAILURE	AuthenticationFailureEvent

Symfony\Component\Security\Core\AuthenticationEvents

Doctrine

Name	Events Constant	Event Object
preRemove	Events::preRemove	LifecycleEventArgs
postRemove	Events::postRemove	LifecycleEventArgs
prePersist	Events::prePersist	LifecycleEventArgs
postPersist	Events::postPersist	LifecycleEventArgs
preUpdate	Events::preUpdate	PreUpdateEventArgs
postUpdate	Events::postUpdate	LifecycleEventArgs
postLoad	Events::postLoad	LifecycleEventArgs
loadClassMetadata	Events::loadClassMetadata	LifecycleEventArgs
preFlush	Events::preFlush	PreFlushEventArgs
onFlush	Events::onFlush	LifecycleEventArgs
postFlush	Events::postFlush	LifecycleEventArgs
onClear	Events::onClear	LifecycleEventArgs

Doctrine\ORM\Events

Service definition

services:
    app.store_manager:
        class: AppBundle\Manager\Store
        arguments:
            - @event_dispatcher

    app.user_event_listener:
        class: AppBundle\EventListener\UserEventListener
        tags:
            - { name: kernel.event_listener,
                event: user.login,
                method: onLogin }
            - { name: kernel.event_listener,
                event: user.update,
                method: onUpdate,
                priority: -1 }

    app.store_event_listener:
        class: AppBundle\EventListener\StoreListener
        tags:
            - { name: kernel.event_subscriber }

Tags:

kernel.event_listener
kernel.event_subscriber

Service:

event_dispatcher

/!\ Doctrine /!\

doctrine:
    dbal:
        default_connection: default
        connections:
            default:
                driver: pdo_sqlite
                memory: true

services:
    my.listener:
        class: Acme\SearchBundle\EventListener\SearchIndexer
        tags:
            - { name: doctrine.event_listener, event: postPersist }
    my.listener2:
        class: Acme\SearchBundle\EventListener\SearchIndexer2
        tags:
            - { name: doctrine.event_listener, event: postPersist, connection: default }
    my.subscriber:
        class: Acme\SearchBundle\EventListener\SearchIndexerSubscriber
        tags:
            - { name: doctrine.event_subscriber, connection: default }

Tags:

doctrine.event_listener
doctrine.event_subscriber

Tools

Commands

$ app/console debug:event-dispatcher -h
Usage:
  debug:event-dispatcher [options] [--] [<event>]

Arguments:
  event                    An event name

Options:
      --format=FORMAT      The output format  (txt, xml, json, or md) [default: "txt"]
      --raw                To output raw description
      ...

Help:
 The debug:event-dispatcher command displays all configured listeners:

   php app/console debug:event-dispatcher

 To get specific listeners for an event, specify its name:

   php app/console debug:event-dispatcher kernel.request

$ app/console debug:event-dispatcher
[event_dispatcher] Registered listeners by event

[Event] console.command
+-------+-------------------------------------------------------------------------------+
| Order | Callable                                                                      |
+-------+-------------------------------------------------------------------------------+
| #1    | Symfony\Component\HttpKernel\EventListener\DebugHandlersListener::configure() |
| #2    | Symfony\Bridge\Monolog\Handler\ConsoleHandler::onCommand()                    |
| #3    | Symfony\Bridge\Monolog\Handler\ConsoleHandler::onCommand()                    |
+-------+-------------------------------------------------------------------------------+

[Event] console.terminate
+-------+-----------------------------------------------------------------------------------+
| Order | Callable                                                                          |
+-------+-----------------------------------------------------------------------------------+
| #1    | Symfony\Bundle\SwiftmailerBundle\EventListener\EmailSenderListener::onTerminate() |
| #2    | Symfony\Bridge\Monolog\Handler\ConsoleHandler::onTerminate()                      |
| #3    | Symfony\Bridge\Monolog\Handler\ConsoleHandler::onTerminate()                      |
+-------+-----------------------------------------------------------------------------------+

[Event] kernel.controller
+-------+-----------------------------------------------------------------------------------------------+
| Order | Callable                                                                                      |
+-------+-----------------------------------------------------------------------------------------------+
| #1    | Symfony\Bundle\FrameworkBundle\DataCollector\RouterDataCollector::onKernelController()        |
| #2    | Symfony\Component\HttpKernel\DataCollector\RequestDataCollector::onKernelController()         |
| #3    | Sensio\Bundle\FrameworkExtraBundle\EventListener\ControllerListener::onKernelController()     |
| #4    | Sensio\Bundle\FrameworkExtraBundle\EventListener\ParamConverterListener::onKernelController() |
| #5    | Sensio\Bundle\FrameworkExtraBundle\EventListener\HttpCacheListener::onKernelController()      |
| #6    | Sensio\Bundle\FrameworkExtraBundle\EventListener\SecurityListener::onKernelController()       |
| #7    | Sensio\Bundle\FrameworkExtraBundle\EventListener\TemplateListener::onKernelController()       |
+-------+-----------------------------------------------------------------------------------------------+

[Event] kernel.exception
+-------+-----------------------------------------------------------------------------------+
| Order | Callable                                                                          |
+-------+-----------------------------------------------------------------------------------+
| #1    | Symfony\Component\HttpKernel\EventListener\ProfilerListener::onKernelException()  |
| #2    | Symfony\Component\HttpKernel\EventListener\ExceptionListener::onKernelException() |
+-------+-----------------------------------------------------------------------------------+

[Event] kernel.finish_request
+-------+----------------------------------------------------------------------------------------+
| Order | Callable                                                                               |
+-------+----------------------------------------------------------------------------------------+
| #1    | Symfony\Component\HttpKernel\EventListener\LocaleListener::onKernelFinishRequest()     |
| #2    | Symfony\Component\HttpKernel\EventListener\TranslatorListener::onKernelFinishRequest() |
| #3    | Symfony\Component\HttpKernel\EventListener\RouterListener::onKernelFinishRequest()     |
| #4    | Symfony\Component\Security\Http\Firewall::onKernelFinishRequest()                      |
+-------+----------------------------------------------------------------------------------------+

Symfony Profiler

What next ?

https://github.com/symfony/symfony/pull/10823

Must read/watch

Source code	https://github.com/symfony/EventDispatcher
Documentation	http://symfony.com/doc/current/components/event_dispatcher
How Kris Builds Symfony Apps	https://youtu.be/W8MOIOyPbmM
EventDispatcher in C	https://github.com/symfony/symfony/pull/10823

Event Dispatcher

Sommaire

Problem

Design Pattern

Mediator Pattern

Mediator

Symfony EventDispatcher

Install

1. Events

2. Dispatcher

3. Listeners

Event Names

have a unique name

Event Names

Event Objects

Instances of

Event Objects

Dispatcher

Use a Single Instance

Dispatcher

Dispatcher

Dispatcher Extras

Listeners

Reminder: PHP Callable

Subscribers

Subscribers

Stop propagation

Dig in Symfony

Workflow

List of Events

Kernel

Console

Form

Security

Doctrine

Kernel

Console

Form

Security

Doctrine

Service definition

/!\ Doctrine /!\

Tools

Commands

Symfony Profiler

What next ?

Must read/watch

Questions

?

Symfony Event Dispatcher

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