Writing Extensible Code Using Event Dispatcher

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

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

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

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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

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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

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DemCrookidWigitz.com

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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

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0Before We Begin

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0Before We Begin UTION CAUTION CAUTION CAUTIO

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The Code In This Presentation Is Not Production-Ready

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1Procedural PHP

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Procedural PHP $_POST = array( 'name' => 'John Kary', 'email' => 'john@johnkary.net', ); $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: accounts@demcrookidwigitz.com'; $headers[] = 'Reply-To: contact@demcrookidwigitz.com'; $headers[] = 'X-Mailer: PHP/' . phpversion(); mail($to, $subject, $message, implode($headers, "\r\n"));

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2 Object-Oriented PHP

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Object-Oriented PHP $_POST = array( 'name' => 'John Kary', 'email' => 'john@johnkary.net', ); $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: accounts@demcrookidwigitz.com'; $headers[] = 'Reply-To: contact@demcrookidwigitz.com'; $headers[] = 'X-Mailer: PHP/' . phpversion(); mail($to, $subject, $message, implode($headers, "\r\n")); Customer

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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; } }

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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: accounts@demcrookidwigitz.com'; $headers[] = 'Reply-To: help@demcrookidwigitz.com'; $headers[] = 'X-Mailer: PHP/' . phpversion(); return implode($headers, "\r\n"); } }

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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

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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

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3Disk Logging

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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); } }

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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

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4More Disk Logging

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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); } }

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5Moar Logging!

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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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

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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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); $eLog->log($customer->getName() . ' cancelled their order...');

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Your Codebase Is Growing

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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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

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

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Model View Controller

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What is the Responsibility of a Controller?

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Controllers should contain LOGIC

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Controllers should contain LOGIC

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Controllers should contain LOGIC

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Controllers as Glue Custom Application Code Framework Controller

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Controllers as Glue Custom Application Code Controller

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Controllers as Glue Custom Application Code Controller

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Event Dispatcher

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

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

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

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

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Event Dispatcher - Concept Request Response kernel.controller kernel.request kernel.response kernel.view user.login user.register $user

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Event Dispatcher - Concept Request Response kernel.controller kernel.request kernel.response kernel.view user.login user.register $user $user

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

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Let’s use a more concrete example

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

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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()

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

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Event Dispatcher - Dispatch an Event

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Request Response Event Dispatcher - Dispatch an Event

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

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

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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' => 'bobsmith@gmail.com', )); $event = new CustomerEvent($customer); $this->dispatcher->dispatch('customer.register', $event); } } Customer Event Event Name

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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

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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; } }

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Event Dispatcher - All together now!

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Event Dispatcher - All together now! EventDispatcher

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

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

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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()

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Let’s refactor our Controller

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6 Inject the EventDispatcher

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class Controller { public function __construct(EventDispatcher $dispatcher) { $this->dispatcher = $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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com');

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7Our First Event

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class Controller { public function __construct(EventDispatcher $dispatcher) { $this->dispatcher = $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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com');

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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; } }

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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: accounts@demcrookidwigitz.com';

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); // Wire listeners $listener = 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()); } }

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); // Wire listeners $listener = 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()); } }

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8 Move more code to listeners

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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')); 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()); } }

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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); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); 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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

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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); $dLog = new DiskLogger('/logs/prod.log'); $msg = 'Sent welcome email to '.$customer->getName(); $dLog->log($msg); $eLog = new EmailLogger('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); 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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $bossEmail = 'boss@demcrookidwigitz.com'; // 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?"; } // ... }

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $bossEmail = 'boss@demcrookidwigitz.com'; // 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()); } }

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $bossEmail = 'boss@demcrookidwigitz.com'; // 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()); } }

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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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

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9 Clean Up Other Controllers

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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('boss@demcrookidwigitz.com'); $eLog->log($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('boss@demcrookidwigitz.com'); $eLog->log($customer->getName() . ' cancelled their order...'); } }

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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); } }

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $bossEmail = 'boss@demcrookidwigitz.com'; // 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!"; } // ... }

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $bossEmail = 'boss@demcrookidwigitz.com'; // 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()); } }

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1 0 Our Second Event

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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); $event = new CustomerEvent($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); } }

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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; } }

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $diskLogger = new DiskLogger('/logs/prod.log'); // 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()); } }

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $diskLogger = new DiskLogger('/logs/prod.log'); // 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()); } }

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use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $diskLogger = new DiskLogger('/logs/prod.log'); $twitter = new Twitter('demcrookidwigitz', 'b3@tb0Xpr0$'); $bossEmail = 'boss@demcrookidwigitz.com'; // 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

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Caveats

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Listeners are notified in the order registered

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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('mikesmith@gmail.com'); $event = new CustomerEvent($customer); $dispatcher->dispatch('customer.register', $event); First Second

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unless a Priority integer is given when registering a listener

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Caveat - Priority use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $dispatcher->addListener('customer.register', function(CustomerEvent $event) { // Second }, 100); $dispatcher->addListener('customer.register', function(CustomerEvent $event) { // First }, 200); $customer = new Customer(); $customer->setEmail('mikesmith@gmail.com'); $event = new CustomerEvent($customer); $dispatcher->dispatch('customer.register', $event); First Second

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Caveat - Priority use Symfony\Component\EventDispatcher\EventDispatcher; $dispatcher = new EventDispatcher(); $dispatcher->addListener('customer.register', 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('mikesmith@gmail.com'); $event = new CustomerEvent($customer); $dispatcher->dispatch('customer.register', $event); First Third Second

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Don’t rely on priority

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Objects attached to Events are passed by reference

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

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

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Can make debugging difficult

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Just ask a developer

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Just ask a developer

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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%

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Ideas for Utilizing Events

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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?

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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

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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/

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