Magento 2 Observers

December 10, 2015 - Fire development, Magento 2

Observers in Magento 2

This article sheds light on Magento 2 observers – event handlers that listen to events they are attached to and respond to these events. Since Magento 2 signifiantly differs from 1.X, the observers registration and creation include some new aspects described below.

The first important change is the usage of an independent events.xml file, which is necessary for observer registration.
The second difference introduced in Magento 2 is related to the way the system defines the scope of the observer. If previously the xml node has been used, now the system relies on the events.xml file location.
The last vital aspect you should pay attention to is a revamped XML syntax.

Table of contents

Magento 2 Observers: Separate events.xml
Magento 2 Observers: The observer scope definition
Magento 2 Observers: Other useful materials

Magento 2 Observers: Separate events.xml

As we’ve mentioned above, Magento 2 stores all module observers in an independent xml file under:

app/code/vendor/module/etc/events.xml(app/code/vendor/module/etc/adminhtml/events.xml

1	app/code/vendor/module/etc/events.xml(app/code/vendor/module/etc/adminhtml/events.xml

Another place where you can find them is:

app/code/vendor/module/etc/frontpage/events.xml

1	app/code/vendor/module/etc/frontpage/events.xml

Let’s have a look at the example of an xml file:

<?xml version="1.0" encoding="UTF-8"?>
...
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../../lib/internal/Magento/Framework/Event/etc/events.xsd">
   <event name="controller_front_send_response_before">
       <observer name="vendor_module_controller_front_send_response_before" instance="vendor/module\Model\Observer" method="verificate" />
   </event>
</config>

<?xml version="1.0" encoding="UTF-8"?>

...

</event>

</config>

You can see the event node and the name attribute that defines a special event which acts as a trigger that calls the observer.

As for the observer node, it defines not only the observer itself, but also its attributes, such as:

name – the registration name of the observer. Not that it shouldn’t coincide;
instance identifies a class and a method executed if a definite event takes place;
method – the executed method.

Now, let’s see how the observer looks like (app/code/vendor/module/Model/Observer.php):

<?php
...
namespace vendor\module\Model;
class Observer
{
   protected $_moduleData;
   protected $_registry = null;
   public function __construct (
       \vendor\module\Helper\Data $moduleData,
       \Magento\Framework\Registry $registry
   ) {
       $this->_moduleData = $moduleData;
       $this->_registry = $registry;
   }
   public function verificate(\Magento\Framework\Event\Observer $observer)
   {  
       ...
   }
   ...
}

<?php

...

namespace vendor\module\Model;

class Observer

{

protected $_moduleData;

protected $_registry = null;

public function __construct (

\vendor\module\Helper\Data $moduleData,

\Magento\Framework\Registry $registry

) {

$this->_moduleData = $moduleData;

$this->_registry = $registry;

}

public function verificate(\Magento\Framework\Event\Observer $observer)

{

...

}

...

}

The only significant difference here is related to the way the classes are named. In the aforementioned example, the verificate function receives a current observer object as an argument.

Magento 2 Observers: The observer scope definition

Now, let’s shed light on the observer scope definition mentioned above. Just look at the following config.xml file:

<frontend>
   <events>
       <vendor_jquery_dispatch_before>
           <observers>
               <vendor_module_jquery_dispatch_before>
                   <type>singleton</type>
                   <class>module/observer</class>
                   <method>verificate</method>
               </vendor_module_jquery_dispatch_before>
           </observers>
       </vendor_jquery_dispatch_before>
   </events>
</frontend>

<vendor_jquery_dispatch_before>

<vendor_module_jquery_dispatch_before>

<type>singleton</type>

<class>module/observer</class>

<method>verificate</method>

</vendor_module_jquery_dispatch_before>

</observers>

</vendor_jquery_dispatch_before>

</events>

</frontend>

In case of 1.x, this approach has been used to define the observer on the frontend only. However, Magento 2 defines the scope of the observer by the events.xml file and its location.

For frontend it is

app/code/Namespace/Modulename/etc/frontend/

1	app/code/Namespace/Modulename/etc/frontend/

For admin:

app/code/Namespace/Modulename/etc/adminhtml/

1	app/code/Namespace/Modulename/etc/adminhtml/

For both locations:

app/code/Namespace/Modulename/etc/

1	app/code/Namespace/Modulename/etc/

Source

Magento 2 Observers: Other useful materials

If you are not familiar with events.xml configuration files, they contain event/observer configuration. Their stage is characterised with two terms: global and area. As for the Configuration object, it is \Magento\Framework\Event. For further information, check this manual: Module configuration files.

In its turn, Magento\Framework\Event includes the code responsible for publishing synchronous events as well as handling observers for any Magento event. For further information, follow this link: Magento Framework.

The way you can get the list of events/observers in Magento 2 is described here: How to get Magento 2 events/observers.

If you want to handle events:

Take a module’s events.xml file and declare event handlers there.
Check the following example of event handler declaration:

<?xml version='1.0'?>
<config xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xsi:noNamespaceSchemaLocation='../../../../../lib/internal/Magento/Framework/Event/etc/events.xsd'>
            <event name='controller_action_predispatch'>
                        <observer
                                    name='Df\Core\Observer\ControllerActionPredispatch'
                                    instance='Df\Core\Observer\ControllerActionPredispatch'
                        />
            </event>
</config>

<?xml version='1.0'?>

<observer

name='Df\Core\Observer\ControllerActionPredispatch'

instance='Df\Core\Observer\ControllerActionPredispatch'

</event>

</config>

Now, you can create a new event handler class. Note that it should implement ObserverInterface with a single execute method. The interface should be handled as follows:

<?php
namespace Df\Core\Observer;
use Magento\Framework\Event\ObserverInterface;
class ControllerActionPredispatch implements ObserverInterface {
    /**
    * @override
    * @see ObserverInterface::execute()
    * @used-by \Magento\Framework\Event\Invoker\InvokerDefault::_callObserverMethod()
    * @see \Magento\Framework\App\Action\Action::dispatch()
    * https://github.com/magento/magento2/blob/dd47569249206b217e0a9f9a9371e73fd7622724/lib/internal/Magento/Framework/App/Action/Action.php#L91-L92
        $eventParameters = ['controller_action' => $this, 'request' => $request];
        $this->_eventManager->dispatch('controller_action_predispatch', $eventParameters)
    * @param \Magento\Framework\Event\Observer $observer
    * @return void
    */
    public function execute(\Magento\Framework\Event\Observer $observer) {
        rm_state()->controllerSet($observer['controller_action']);
    }
}