Step 1
Declare event handlers in a module’s events.xml file.
A module can have multiple events.xml files:
| Location | Where do the handlers are triggered | Example |
|---|---|---|
| `etc/events.xml` | Everythere. | [`Magento/CatalogInventory`][1] |
| `etc/adminhtml/events.xml` | In admin interface only. | [`Magento/Catalog`][2] |
| `etc/frontend/events.xml` | In frontend interface only. | [`Magento/Catalog`][3] |
| `etc/crontab/events.xml` | While handling scheduled ([cron][4]) jobs only. | [`Magento/CatalogRule`][5] |
| `etc/setup/events.xml` | While Magento or extensions are being [installed][6] or [upgraded][7]. | [`Magento/CatalogUrlRewrite`][8] |
| `etc/webapi_rest/events.xml` | While handling [REST][9] [API][10] requests. | [`Magento/CatalogRule`][11] |
| `etc/webapi_soap/events.xml` | While handling [SOAP][12] [API][13] requests. | [`Magento/CatalogRule`][14] |
An example of event handler declaration in events.xml:
<?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>
Step 2
Create the event handler class.
The class shoud implement \Magento\Framework\Event\ObserverInterface.
The interface has the single method execute and it shoud be implemented:
<?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']);
}
}
Please note that event handler declaration has been significanlty changed in October 2015:
https://github.com/magento/magento2/commit/d874f15f1ac5b646d3405b778abde088bd1807fd
https://github.com/magento/magento2/commit/4857e62db36e891c26452f4a24e06be1e0a15972