ZF2 Event Managerby Bo Andersen

Introduction to the event systemZF2 is based on the Event-driven Architecture (EDA)

Simply put, the idea is that activities occur in response to events

Thus, activities are attached to events, and when a given event occurs, its attached activities are executed

This principle is well known in programming; Java and the .NET platform, for instance, both make heavy use of event handling

Configuring ZF2 with eventsEvents are used internally in Zend Framework 2, e.g. by the module

manager

Subscribing to these events allows one to “plug into” the framework

A series of pre-defined events are available

Please see the documentation for more information and a full list of available events

Example use caseImagine placing an order on Amazon.com

When the order is placed, a series of activities or processes should occur

A confirmation should be sent to the customer

The items should be picked from the warehouse

The customer’s credit card should be debited

...

These processes are registered on the OnOrderPlaced event, and when this event is triggered, the attached processes or activities are executed

AdvantagesProvides a great deal of flexibility in a system

Easy to add or remove activities that should happen when a given event occurs

The application becomes very flexible, as it is easy to “hook into” the system

Business processes can easily be adapted to changing business needs

DisadvantagesIt can be hard to understand what actually happens during a business

process

Activities can be attached to events almost anywhere in the application, and perhaps even added dynamically

This makes it difficult to both understand and debug a process; one must know which activities are attached to an event at runtime to understand exactly what happens

The flow of the business process is therefore less transparent than if it were implemented in a completely procedural fashion

The sequence in which activities must be executed adds complexity

Activities may depend upon each other; for instance, a customer’s credit card should not be debited before the items are picked from the warehouse.

The Event Manager

Example: Triggering an eventclass UserService implements EventManagerAwareInterface {

public function setEventManager(EventManagerInterface $events) { /* ... */ }

public function getEventManager() { /* ... */ }

public function register(User $user) {

$this->getEventManager()->trigger(__function__ . '.pre', $this, array(‘user’ => $user));

// Register code here

$this->getEventManager()->trigger(__function__ . '.post', $this, array(‘user’ => $user));

}

}

Example: Attaching event listener$userService = new UserService();

$userService->setEventManager(new EventManager());

$userService->getEventManager()->attach('register.post', function(EventInterface $event) {

$logger = new \Zend\Log\Logger();

$logger->addWriter(new \Zend\Log\Writer\Stream('php://output'));

$logger->log(Zend\Log\Logger::INFO, 'New user (ID: ' . $event->getParam('user')->getId() . ')');

});

More informationA priority can also be specified when attaching an event listener to an

event

The priority is simply an integer; the listener with the highest number is executed first

A callback can be assigned to multiple events at once

A wildcard can also be used to attach a callback to all events

More information and examples: http://tinyurl.com/zf2-event-manager

that’s allThis presentation is part of my Zend Framework 2 online course.

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