Skip to main content

Symfony Tutorials: Event Dispatcher

Image
By
Symfony Tutorials: Event Dispatcher

 Symfony EventDispatcher is object which interacts with different set of objects when certain event happens.

To illustrate Event Dispatcher definition let’s consider the online shopping website example.

suppose you want to purchase a mobile from online shopping website , but unfortunately that mobile is out of stock.

Then you subscribe into online shopping website for this mobile availability.

When mobile comes in stock, online shopping website notifies you about mobile phone’s availability via email.

In above scenario


  • you are the Event Listener / Event Subscriber
  • mobile availability is Event
  • online shopping website is Event Dispatcher.



Symfony EventDispatcher works in same manner.for example, whenever there is HTTP request, Kernel creates a request object and it dispatches an event kernel.request.

Whoever subscribes to kernel.request event gets notified.

So here you might be having few questions in my mind.

What is Event?

Event object describe what event is and add some additional information so that its listener or subscriber can get enough information about event.

What is EventDispatcher?

EventDispatcher is central object which dispatches the event to all its listener or subscriber.
EventDispatcher maintains the list of all listeners of a particular Event.

use Symfony\Component\EventDispatcher\EventDispatcher;

$dispatcher =new EventDispatcher();

What is Event Listener?

Listener is a object which performs a task whenever a associated event happens. 
But first we need to attach listener to Event Dispatcher for a particular event.

$listener=new MobileAvailabilityListener();
$dispatcher->addListener('store.mobile.available',array($listener,'sendEmailToUsers'));

Considering Online Shopping Store example let’s create a custom event and dispatch this event.

Here we want to create mobile availability event which get dispatched whenever mobile is available.

First we create static event class which holds event name and its instance information

Static Event Class


final class MobileEvents
{
/**
     * The store.mobile.available event is thrown each time when mobile 
  * is available in store
     *
     * The event listener receives an
     * Acme\StoreBundle\Event\MobileAvailableEvent instance.
     *
     * @var string
     */
const MOBILE_AVAILABLE='store.mobile.available';
}
Later, create actual event object.

Symfony uses Symfony\Component\EventDispatcher\Event class.

This class wont give us enough information about mobile availability therefor we need to subclass it and add additional information.

namespace Acme\StoreBundle\Event;

use Symfony\Component\EventDispatcher\Event;
use Acme\StoreBundle\Mobile;

class MobileAvailableEvent
{
  protected $mobile;

  public function__construct(Mobile $mobile)
  {
    $this->mobile=$mobile;
  }

  public function getMobile()
  {
    return $this->mobile;
  }
}

Later, create event listener, which sends emails to user regarding availability of the mobile phone.

use Acme\StoreBundle\Event\MobileAvailableEvent;

class MobileAvailabilityListener
{
  // ...

  public function sendEmailToUsers(MobileAvailableEvent $event)
  {
     // ... send email to users
  }
}


Now all is set, let’s attach this listener to the dispatcher. And dispatch the event.
use Symfony\Component\EventDispatcher\EventDispatcher;
use Acme\StoreBundle\Event\MobileAvailableEvent;
use Acme\StoreBundle\Event\MobileAvailabilityListener;
use Acme\StoreBundle\Entity\Mobile;

$dispatcher = new EventDispatcher();

// attach listener
$listener = new MobileAvailabilityListener();
$dispatcher->addListener(MobileEvents::MOBILE_AVAILABLE, array($listener, 'sendEmailToUsers'));

//if mobile is available then dispatch the event
$mobile = new Mobile();
$event = new MobileAvailableEvent($mobile);
$dispatcher->dispatch(MobileEvents::MOBILE_AVAILABLE, $event);

This is a every basic example, you can create event for user registration process and can send confirmation email via event listener or can do  many things using Symfony Event Dispatcher.
Labels:

Comments

Post a Comment

Subscribe for latest tutorial updates

* indicates required

Popular posts from this blog

AJAX - How To Retrieve JSON Response from PHP script

By
Hello Friends, This is my first tutorial post. Today I'll explain you how to retrieve JSON response via Ajax call. First we build a PHP script to send response in JSON format, then we will gather this response from an Ajax call through jQuery script. Let’s first create a PHP script  Create a PHP script, I’ll name it as “json_response.php” And add following code in it json_response.php <?php //set header for JSON response header("Content-Type: application/json"); //render array in JSON format echo json_encode(array('status' => 200, 'message' => 'Response from PHP script in JSON format.')); This is a basic example to send JSON response. PHP script will send response with status code and message. Now create a HTML file to fetch JSON response and add it in header tag. Create a HTML file, I’ll name it as “json_response.html” And add following code. json_response.html <html>           ...
Post a Comment
Read more

JSON Tutorials : Getting Started

By
JSON is widely accepted text formatted structured data. JSON stands for " JavaScript Object Notation ". In general JSON can represent 1. Object of database record. 2. Object to represent a list of HTML elements. 3. Result of search query. 4. Response of an Ajax call. Here you can see JSON is used in many different areas and for many different scenarios. This means it has simple data structure. most of programming languages adopt it and it can flow easily from one connection to another. You can find JSON office definition here JSON Official Site . JSON is represented by two structural types, which includes two primitive types. Structural types Array : A sequential list of primitive data types between square brackets [ ] Object : Collection of key, value pair stored inside curly braces { }, where value would be primitive data type Primitive types : There are two primitive types key and value. " key " should be string and " value (data type)...
Post a Comment
Read more

Twig Tutorials: Install and Configure

By
In this tutorial, we'll look at how to install Twig within your PHP project and thereafter configure it so that we can create and use a Twig template inside our PHP web application. Later on, we'll see a simple Twig template example that displays a "Welcome to Twig template" message. Let's take it one step at a time. Install The Twig template can be installed using Composer, Git, or PEAR. In this tutorial, we will use Composer to install Twig. To do so, we'll need to make a "composer.json" file. { "require" : { "twig/twig" : "1.*" } } From the console, run the following command . $ php composer.phar install This command will install Twig library. Configuration To use the Twig template, we should first configure it. To achieve this, we will write an index.php file which will configure the Twig autoloader and generate the Twig environment. We will render the Twig temp...
Post a Comment
Read more