Writing Extensible Code Using Event Dispatcher

WRITING EXTENSIBLE CODE USING EVENT DISPATCHER John Kary Kansas City
PHP User Group, October 2012

ABOUT PHP since 2005 Contract PHP Developer in Lawrence Education
& Trucking Industry Previously of University of Kansas - IT

EventDispatcher http://bit.ly/sf2-event-dispatcher { "require": { "symfony/event-dispatcher": "dev-master" } } php
composer.phar update

Overview 1. Procedural PHP 2. Refactor to Object-Oriented PHP 3.
Extensibility 4. Controllers in Model View Controller 5. EventDispatcher concept 6. Refactor to using an EventDispatcher 7. EventDispatcher caveats

Maybe you know about... JavaScript Events Basics of Object-Oriented Programming
Inheritance Polymorphism Encapsulation Abstraction Delegation Dependency Injection Single Responsibility Principle Separation of Concerns MVC

DemCrookidWigitz.com

John, Customers are unhappy. Send them a “Welcome!” email after
they register on the web site. Tell them we are glad to have them as a customer. That’ll teach ‘em. Do it now. The Boss The Boss

0Before We Begin

0Before We Begin UTION CAUTION CAUTION CAUTIO

The Code In This Presentation Is Not Production-Ready

1Procedural PHP

Procedural PHP $_POST = array( 'name' => 'John Kary', 'email'
=> '[email protected]', ); $to = $_POST['email']; $subject = 'New Account'; $message = "Welcome " . $_POST['name'] . "! Your new space has been created! Use this link to login: https://activate.demcrookidwidgitz.com/code/Sq9284tWBnWgpjw Thanks! DemCrookidWigitz"; $headers = array(); $headers[] = 'From: [email protected]'; $headers[] = 'Reply-To: [email protected]'; $headers[] = 'X-Mailer: PHP/' . phpversion(); mail($to, $subject, $message, implode($headers, "\r\n"));

2 Object-Oriented PHP

Object-Oriented PHP $_POST = array( 'name' => 'John Kary', 'email'
=> '[email protected]', ); $to = $_POST['email']; $subject = 'New Account'; $message = "Welcome " . $_POST['name'] . "! Your new space has been created! Use this link to login: https://activate.demcrookidwidgitz.com/code/Sq9284tWBnWgpjw Thanks! DemCrookidWigitz"; $headers = array(); $headers[] = 'From: [email protected]'; $headers[] = 'Reply-To: [email protected]'; $headers[] = 'X-Mailer: PHP/' . phpversion(); mail($to, $subject, $message, implode($headers, "\r\n")); Customer

Object-Oriented PHP class Customer { public function __construct(array $data) {
$this->name = $data['name']; $this->email = $data['email']; } public function getName() { return $this->name; } public function getEmail() { return $this->email; } }

=> '[email protected]', ); $to = $_POST['email']; $subject = 'New Account'; $message = "Welcome " . $_POST['name'] . "! Your new space has been created! Use this link to login: https://activate.demcrookidwidgitz.com/code/Sq9284tWBnWgpjw Thanks! DemCrookidWigitz"; $headers = array(); $headers[] = 'From: [email protected]'; $headers[] = 'Reply-To: [email protected]'; $headers[] = 'X-Mailer: PHP/' . phpversion(); mail($to, $subject, $message, implode($headers, "\r\n")); Customer WelcomeEmail

class WelcomeEmail { public function send($to, $name) { return mail($to,
$this->getSubject(), $this->getMessage($name), $this->getHeaders()); } protected function getSubject() { return 'New Account'; } protected function getMessage($name) { return "Welcome " . $name . "! Your new space has been created! Use this link to login: https://activate.demcrookidwigitz.com/code/Sq9284tWBnWgpjw Thanks! DemCrookidWigitz"; } protected function getHeaders() { $headers = array(); $headers[] = 'From: [email protected]'; $headers[] = 'Reply-To: [email protected]'; $headers[] = 'X-Mailer: PHP/' . phpversion(); return implode($headers, "\r\n"); } }

=> '[email protected]', ); $to = $_POST['email']; $subject = 'New Account'; $message = "Welcome " . $_POST['name'] . "! Your new space has been created! Use this link to login: https://activate.demcrookidwidgitz.com/code/Sq9284tWBnWgpjw Thanks! DemCrookidWigitz"; $headers = array(); $headers[] = 'From: [email protected]'; $headers[] = 'Reply-To: [email protected]'; $headers[] = 'X-Mailer: PHP/' . phpversion(); mail($to, $subject, $message, implode($headers, "\r\n")); Customer WelcomeEmail Controller

class Controller { // POST http://demcrookidwigitz.com/person public function newCustomer() {
$customer = new Customer($_POST); $email = new WelcomeEmail(); $email->send($customer->getEmail(), $customer->getName()); } } Object-Oriented PHP

John, Advertising wants to know how many new customers we’re
getting. Setup some logging. I don’t want their grubby hands on the database. That’ll teach ‘em. Do it now. The Boss The Boss

3Disk Logging

Disk Logging class Controller { public function newCustomer() { $customer
= new Customer($_POST); $email = new WelcomeEmail(); $email->send($customer->getEmail()); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(). ' at '.$customer->getEmail(); $dLog->log($msg); } }

John, Marketing wants to run statistics on orders. Keep them
away from the database too. Just add to that other log ﬁle we setup for Advertising. That’ll teach ‘em. Do it now. The Boss The Boss

4More Disk Logging

More Disk Logging class Controller { public function newCustomer() {
// ... $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(). ' at '.$customer->getEmail(); $dLog->log($msg); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); } }

5Moar Logging!

class Controller { public function newCustomer() { // ... $dLog
= new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(). ' at '.$customer->getEmail(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

class Controller { public function newCustomer() { // ... $dLog
= new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(). ' at '.$customer->getEmail(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName().' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...');

Your Codebase Is Growing

class Controller { public function newCustomer() { $customer = new
Customer($_POST); $email = new WelcomeEmail(); $email->send($customer->getEmail()); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

Extensibility [A] system design principle where the implementation takes into
consideration future growth. Extensibility - Wikipedia http://en.wikipedia.org/wiki/Extensibility

Customer($_POST); $email = new WelcomeEmail(); $email->send($customer->getEmail()); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

Customer($_POST); $email = new WelcomeEmail(); $email->send($customer->getEmail()); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } } NOT EXTENSIBLE!

Model View Controller

What is the Responsibility of a Controller?

Controllers should contain LOGIC

Controllers as Glue Custom Application Code Framework Controller

Controllers as Glue Custom Application Code Controller

Event Dispatcher

Event Dispatcher - Concept Request Response kernel.controller kernel.request kernel.response kernel.view

Event Dispatcher - Concept Request Response Your Events kernel.controller kernel.request
kernel.response kernel.view

user.login

user.login user.register

user.login user.register $user

user.login user.register $user $user

Event Dispatcher - Register Listeners EventDispatcher AListener named.eventA BListener named.eventB
CListener named.eventC

Let’s use a more concrete example

Event Dispatcher - Register Listeners CartListener:: onAddToCart() EventDispatcher cart.add CustomerListener::
onRegister() customer.register CartListener:: grantDiscount() cart.checkout

Event Dispatcher - Register Listeners use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new
EventDispatcher(); $listener = new CustomerListener(); $dispatcher->addListener('customer.register', array($listener, 'onRegister')); // Register more listeners class CustomerListener { public function onRegister(CustomerEvent $event) { // Do some work } } Any PHP Callable true === is_callable()

EventDispatcher(); $dispatcher->addListener('customer.register', array('CustomerListener', 'onRegister')); // Register more listeners class CustomerListener { public static function onRegister(CustomerEvent $event) { // Do some work } }

EventDispatcher(); $dispatcher->addListener('customer.register', function(CustomerEvent $event) { // Do some work });

Event Dispatcher - Dispatch an Event

Request Response Event Dispatcher - Dispatch an Event

Request Response Event Dispatcher - Dispatch an Event EventDispatcher “customer.register”
CustomerListener:: onRegister() “cart.add” CartListener:: onAddToCart() “cart.checkout” CartListener:: grantDiscount()

Request Response CustomerEvent “customer.register” Customer Event Dispatcher - Dispatch an
Event EventDispatcher “customer.register” CustomerListener:: onRegister() “cart.add” CartListener:: onAddToCart() “cart.checkout” CartListener:: grantDiscount()

Event Dispatcher - Dispatch an Event use Symfony\Component\EventDispatcher\EventDispatcher; class CustomerController
{ public function __construct(EventDispatcher $dispatcher) { $this->dispatcher = $dispatcher; } public function newCustomer() { $customer = new Customer(array( 'first_name' => 'Bob', 'last_name' => 'Smith', 'email' => '[email protected]', )); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } } Customer Event Event Name

Event EventDispatcher “customer.register” CustomerListener:: onRegister() “cart.add” CartListener:: onAddToCart() “cart.checkout” CartListener:: grantDiscount() $this->dispatcher->dispatch('customer.register', $event);

Event EventDispatcher “customer.register” CustomerListener:: onRegister() “cart.add” CartListener:: onAddToCart() “cart.checkout” CartListener:: grantDiscount() “customer.register” CustomerListener:: onRegister()

Event Dispatcher - Handle the Event class CustomerListener { public
function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $name = $event->getName(); $dispatcher = $event->getDispatcher(); // Do something with Customer object } } CustomerEvent “customer.register” Customer

Event Dispatcher - Handle the Event class CustomerListener { public
function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $name = $event->getName(); $dispatcher = $event->getDispatcher(); // Do something with Customer object } }

Event Dispatcher - Handle the Event use Symfony\Component\EventDispatcher\Event; class CustomerEvent
extends Event { protected $customer; public function __construct(Customer $customer) { $this->customer = $customer; } public function getCustomer() { return $this->customer; } }

Event Dispatcher - All together now!

Event Dispatcher - All together now! EventDispatcher

Event Dispatcher - All together now! CartListener:: onAddToCart() CustomerListener:: onRegister()
CartListener:: grantDiscount() EventDispatcher cart.checkout cart.add customer.register

Event Dispatcher - All together now! CartListener:: onAddToCart() CustomerListener:: onRegister()
CartListener:: grantDiscount() EventDispatcher “cart.checkout” CartListener:: grantDiscount() “cart.add” CartListener:: onAddToCart() “customer.register” CustomerListener:: onRegister()

CustomerEvent “customer.register” Customer Event Dispatcher - All together now! CartListener::
onAddToCart() CustomerListener:: onRegister() CartListener:: grantDiscount() EventDispatcher “cart.checkout” CartListener:: grantDiscount() “cart.add” CartListener:: onAddToCart() “customer.register” CustomerListener:: onRegister()

onAddToCart() CustomerListener:: onRegister() CartListener:: grantDiscount() EventDispatcher “cart.checkout” CartListener:: grantDiscount() “cart.add” CartListener:: onAddToCart() “customer.register” CustomerListener:: onRegister() $this->dispatcher->dispatch('customer.register', $event);

onAddToCart() CustomerListener:: onRegister() CartListener:: grantDiscount() EventDispatcher “cart.checkout” CartListener:: grantDiscount() “cart.add” CartListener:: onAddToCart() “customer.register” CustomerListener:: onRegister()

onAddToCart() CustomerListener:: onRegister() CartListener:: grantDiscount() EventDispatcher “cart.checkout” CartListener:: grantDiscount() “cart.add” CartListener:: onAddToCart() “customer.register” CustomerListener:: onRegister() “customer.register” CustomerListener:: onRegister()

onAddToCart() CustomerListener:: onRegister() CartListener:: grantDiscount() EventDispatcher “cart.checkout” CartListener:: grantDiscount() “cart.add” CartListener:: onAddToCart() “customer.register” CustomerListener:: onRegister() “customer.register” CustomerListener:: onRegister() That’s Event Dispatcher!

Let’s refactor our Controller

Customer($_POST); $email = new WelcomeEmail(); $email->send($customer->getEmail()); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } } START

class Controller { public function __construct(EventDispatcher $dispatcher) { $this->dispatcher =
$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $event = new OrderEvent($order); $this->dispatcher->dispatch('order.new', $event); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.new', $event); } public function cancelOrder() { // ... $event = new OrderEvent($order); $this->dispatcher->dispatch('order.cancel', $event); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.cancel', $event); } } FINISH

6 Inject the EventDispatcher

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $email = new WelcomeEmail(); $email->send($customer->getEmail()); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]');

7Our First Event

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $email = new WelcomeEmail(); $email->send($customer->getEmail()); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]');

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]');

use Symfony\Component\EventDispatcher\Event; class CustomerEvent extends Event { protected $customer; public
function __construct(Customer $customer) { $this->customer = $customer; } public function getCustomer() { return $this->customer; } }

use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); // Wire listeners $listener
= new CustomerEmailListener(new WelcomeEmail()); $dispatcher->addListener('customer.register', array($listener, 'onRegister')); class WelcomeEmail { public function send($to, $name) { return mail($to, $this->getSubject(), $this->getMessage($name), $this->getHeaders()); } protected function getSubject() { return 'New Account'; } protected function getMessage($name) { return "Welcome " . $name . "! Your new space has been created! Use this link to login: https://activate.demcrookidwigitz.com/code/Sq9284tWBnWgpjw Thanks! DemCrookidWigitz"; } protected function getHeaders() { $headers = array(); $headers[] = 'From: [email protected]';

= new CustomerEmailListener(new WelcomeEmail()); $dispatcher->addListener('customer.register', array($listener, 'onRegister'));

= new CustomerEmailListener(new WelcomeEmail()); $dispatcher->addListener('customer.register', array($listener, 'onRegister')); class CustomerEmailListener { public function __construct(WelcomeEmail $email) { $this->email = $email; } public function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getEmail(), $customer->getName()); } }

= new CustomerEmailListener(new WelcomeEmail()); $dispatcher->addListener('customer.register', array($listener, 'onRegister')); class CustomerEmailListener { public function __construct(WelcomeEmail $email) { $this->email = $email; } public function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getEmail(), $customer->getName()); } } class WelcomeEmail { public function send($to, $name) { return mail($to, $this->getSubject(), $this->getMessage($name), $this->getHeaders()); } }

8 Move more code to listeners

use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $diskLogger = new DiskLogger('/logs/prod.log');
// Wire listeners $listener = new CustomerEmailListener(new WelcomeEmail(), $diskLogger); $dispatcher->addListener('customer.register', array($listener, 'onRegister'));

// Wire listeners $listener = new CustomerEmailListener(new WelcomeEmail(), $diskLogger); $dispatcher->addListener('customer.register', array($listener, 'onRegister')); class CustomerEmailListener { public function __construct(WelcomeEmail $email) { $this->email = $email; } public function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getEmail(), $customer->getName()); } }

// Wire listeners $listener = new CustomerEmailListener(new WelcomeEmail(), $diskLogger); $dispatcher->addListener('customer.register', array($listener, 'onRegister')); class CustomerEmailListener { public function __construct(WelcomeEmail $email) { $this->email = $email; } public function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getEmail(), $customer->getName()); } } class CustomerEmailListener { public function __construct(WelcomeEmail $email, DiskLogger $logger) { $this->email = $email; $this->logger = $logger; } public function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getEmail(), $customer->getName()); } }

// Wire listeners $listener = new CustomerEmailListener(new WelcomeEmail(), $diskLogger); $dispatcher->addListener('customer.register', array($listener, 'onRegister')); class CustomerEmailListener { public function __construct(WelcomeEmail $email) { $this->email = $email; } public function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getEmail(), $customer->getName()); } } class CustomerEmailListener { public function __construct(WelcomeEmail $email, DiskLogger $logger) { $this->email = $email; $this->logger = $logger; } public function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getEmail(), $customer->getName()); } } class CustomerEmailListener { public function __construct(WelcomeEmail $email, DiskLogger $logger) { $this->email = $email; $this->logger = $logger; } public function onRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getEmail(), $customer->getName()); $this->logger->log('Sent welcome email to ' . $customer->getName()); } }

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); class Controller { public function __construct(EventDispatcher $dispatcher) { $this->dispatcher = $dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $bossEmail = '[email protected]'; //
Wire listeners // ... $listener = new BossNewCustomerEmailListener(new BossNewCustomerEmail($bossEmail)); $dispatcher->addListener('customer.register', array($listener, 'onCustomerRegister'));

Wire listeners // ... $listener = new BossNewCustomerEmailListener(new BossNewCustomerEmail($bossEmail)); $dispatcher->addListener('customer.register', array($listener, 'onCustomerRegister')); class BossNewCustomerEmail { public function __construct($bossEmail) { $this->bossEmail = $bossEmail; } public function send($name) { return mail($this->bossEmail, $this->getSubject(), $this->getMessage($name), $this->getHeaders()); } protected function getSubject() { return 'New Customer Registered!'; } protected function getMessage($name) { return "Boss! " . $name . " just registered! Sweet, huh?"; } // ... }

Wire listeners // ... $listener = new BossNewCustomerEmailListener(new BossNewCustomerEmail($bossEmail)); $dispatcher->addListener('customer.register', array($listener, 'onCustomerRegister'));

Wire listeners // ... $listener = new BossNewCustomerEmailListener(new BossNewCustomerEmail($bossEmail)); $dispatcher->addListener('customer.register', array($listener, 'onCustomerRegister')); class BossNewCustomerEmailListener { public function __construct(BossNewCustomerEmail $email) { $this->email = $email; } public function onCustomerRegister(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getName()); } }

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' has registered!'); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } } class Controller { public function __construct(EventDispatcher $dispatcher) { $this->dispatcher = $dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

9 Clean Up Other Controllers

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $twitter->tweet($customer->getName() . ' just ordered from us!'); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } } class Controller { public function __construct(EventDispatcher $dispatcher) { $this->dispatcher = $dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.new', $event); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $twitter = new Twitter('demcrookidwigitz',
'b3@tb0Xpr0$'); // Wire listeners $listener = new TwitterListener($twitter); $dispatcher->addListener('order.new', array($listener, 'tweetAtOrderer'));

use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $twitter = new Twitter('demcrookidwigitz',
'b3@tb0Xpr0$'); // Wire listeners $listener = new TwitterListener($twitter); $dispatcher->addListener('order.new', array($listener, 'tweetAtOrderer')); class TwitterListener { public function __construct(Twitter $twitter) { $this->twitter = $twitter; } public function tweetAtOrderer(CustomerEvent $event) { $customer = $event->getOrder(); $msg = $customer->getTwitterHandle().' Thanks for ordering from us!'; $this->twitter->tweet($msg); } }

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.new', $event); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $eLog = new EmailLogger('[email protected]'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

Wire listeners // ... $listener = new BossCancelOrderEmailListener(new BossCancelOrderEmail($bossEmail)); $dispatcher->addListener('customer.order.cancel', array($listener, 'onCancelOrder')); class BossCancelOrderEmail { public function __construct($bossEmail) { $this->bossEmail = $bossEmail; } public function send($name) { return mail($this->bossEmail, $this->getSubject(), $this->getMessage($name), $this->getHeaders()); } protected function getSubject() { return 'Customer Order Cancelled'; } protected function getMessage($name) { return "Boss! " . $name . " cancelled their order. Bummer!"; } // ... }

Wire listeners // ... $listener = new BossCancelOrderEmailListener(new BossCancelOrderEmail($bossEmail)); $dispatcher->addListener('customer.order.cancel', array($listener, 'onCancelOrder')); class BossCancelOrderEmailListener { public function __construct(BossCancelOrderEmail $email) { $this->email = $email; } public function onCancelOrder(CustomerEvent $event) { $customer = $event->getCustomer(); $this->email->send($customer->getName()); } }

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.new', $event); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.cancel', $event); } }

1 0 Our Second Event

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.new', $event); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.cancel', $event); } }

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Created order ' . $number); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.new', $event); } public function cancelOrder() { // ... $dLog = new DiskLogger('/logs/prod.log'); $dLog->log('Cancelled order number ' . $number); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.cancel', $event); } } class Controller { public function __construct(EventDispatcher $dispatcher) { $this->dispatcher = $dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $event = new OrderEvent($order); $this->dispatcher->dispatch('order.new', $event); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.new', $event); } public function cancelOrder() { // ... $event = new OrderEvent($order); $this->dispatcher->dispatch('order.cancel', $event); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.cancel', $event); } }

use Symfony\Component\EventDispatcher\Event; class OrderEvent extends Event { protected $order; public
function __construct(Order $order) { $this->order = $order; } public function getOrder() { return $this->order; } }

// Wire listeners $listener = new OrderLoggerListener($diskLogger); $dispatcher->addListener('order.new', array($listener, 'onNewOrder')); class OrderLoggerListener { public function __construct(DiskLogger $logger) { $this->logger = $logger; } public function onNewOrder(OrderEvent $event) { $order = $event->getOrder(); $this->logger->log('Created order number ' . $order->getNumber()); } }

// Wire listeners $listener = new OrderLoggerListener($diskLogger); $dispatcher->addListener('order.new', array($listener, 'onNewOrder')); $dispatcher->addListener('order.cancel', array($listener, 'onCancelOrder')); class OrderLoggerListener { public function __construct(DiskLogger $logger) { $this->logger = $logger; } public function onNewOrder(OrderEvent $event) { $order = $event->getOrder(); $this->logger->log('Created order number ' . $order->getNumber()); } public function onCancelOrder(OrderEvent $event) { $order = $event->getOrder(); $this->logger->log('Cancelled order number ' . $order->getNumber()); } }

$dispatcher; } public function newCustomer() { $customer = new Customer($_POST); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } public function createOrder() { // ... $event = new OrderEvent($order); $this->dispatcher->dispatch('order.new', $event); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.new', $event); } public function cancelOrder() { // ... $event = new OrderEvent($order); $this->dispatcher->dispatch('order.cancel', $event); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.order.cancel', $event); } } FINISH

$twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $bossEmail = '[email protected]'; // Wire listeners $listener = new CustomerEmailListener(new WelcomeEmail()); $dispatcher->addListener('customer.register', array($listener, 'onRegister')); $listener = new BossNewCustomerEmailListener(new BossNewCustomerEmail($bossEmail)); $dispatcher->addListener('customer.register', array($listener, 'onCustomerRegister')); $listener = new BossCancelOrderEmailListener(new BossCancelOrderEmail($bossEmail)); $dispatcher->addListener('customer.order.cancel', array($listener, 'onCancelOrder')); $listener = new OrderLoggerListener($diskLogger); $dispatcher->addListener('order.new', array($listener, 'onNewOrder')); $dispatcher->addListener('order.cancel', array($listener, 'onCancelOrder')); $listener = new TwitterListener($twitter); $dispatcher->addListener('order.new', array($listener, 'tweetAtOrderer')); FINISH

Caveats

Listeners are notified in the order registered

Caveat - Priority use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $dispatcher->addListener('customer.register',
function(CustomerEvent $event) { // First }); $dispatcher->addListener('customer.register', function(CustomerEvent $event) { // Second }); $customer = new Customer(); $customer->setEmail('[email protected]'); $event = new CustomerEvent($customer); $dispatcher->dispatch('customer.register', $event); First Second

unless a Priority integer is given when registering a listener

function(CustomerEvent $event) { // Second }, 100); $dispatcher->addListener('customer.register', function(CustomerEvent $event) { // First }, 200); $customer = new Customer(); $customer->setEmail('[email protected]'); $event = new CustomerEvent($customer); $dispatcher->dispatch('customer.register', $event); First Second

function(CustomerEvent $event) { // Third }, 100); $dispatcher->addListener('customer.register', function(CustomerEvent $event) { // First }, 200); $dispatcher->addListener('customer.register', function(CustomerEvent $event) { // Second }, 200); $customer = new Customer(); $customer->setEmail('[email protected]'); $event = new CustomerEvent($customer); $dispatcher->dispatch('customer.register', $event); First Third Second

Don’t rely on priority

Objects attached to Events are passed by reference

which may lead to side effects if you’re not careful

Caveat - Side Eﬀects use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher();
$dispatcher->addListener('customer.register', function(CustomerEvent $event) { echo $event->getCustomer()->getEmail(); // [email protected] $event->getCustomer()->setEmail('[email protected]'); }); $dispatcher->addListener('customer.register', function(CustomerEvent $event) { echo $event->getCustomer()->getEmail(); // [email protected] }); $customer = new Customer(); $customer->setEmail('[email protected]'); $event = new CustomerEvent($customer); $dispatcher->dispatch('customer.register', $event); 1. Set Email 2. Get Email 3. Update Email 4. Email not the same

Can make debugging difficult

Just ask a developer

Adobe Desktop Application Codebase Source: http://stlab.adobe.com/wiki/index.php/File:2008_07_25_google.pdf Event Handling logic All
other logic 33% Event Handling bugs All other bugs 50%

Ideas for Utilizing Events

Ideas for Utilizing Events • Logging • Oﬄoading expensive operations
to a message queue • Email, PDF generation, ﬁle system access • Setting “created_at” or “updated_at” on an entity • Updating a search index when persisting an entity • Allowing users of your plug-ins to extend their functionality without modifying your code • What ideas have you come up with?

Further Reading • Introduction to Symfony2 EventDispatcher http://bit.ly/sf2-event-dispatcher • An
Introduction to Zend Framework 2 Event Manager http://bit.ly/zf2-event-manater • The S.O.L.I.D. Principles of OO and Agile Design http://bit.ly/uncle-bob-oo-insights

Sources • http://lampwww.epfl.ch/~imaier/pub/DeprecatingObserversTR2010.pdf • http://stlab.adobe.com/wiki/index.php/File:2008_07_25_google.pdf Photo Credits • http://www.flickr.com/photos/pedromourapinheiro/2456410959/ •
http://www.flickr.com/photos/seat850/3893504473/ • http://www.flickr.com/photos/slworking/5170065748/ • http://www.flickr.com/photos/33037982@N04/3727397261/ • http://www.flickr.com/photos/factoryjoe/26967479/

John Kary johnkary@ gmail.com @ johnkary Slides @ http://johnkary.net/talks WRITING
EXTENSIBLE CODE USING EVENT DISPATCHER https://joind.in/7551

Writing Extensible Code Using Event Dispatcher

Writing Extensible Code Using Event Dispatcher

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