The very basics of getting started with CakePHP events

This is supposed to clarify what's already in the official documentation at https://book.cakephp.org/3/en/core-libraries/events.html

1. Create a listener. Can be a separate arbitrary class, or an existing class in the MVC scheme of things. (Deciding what would be a good place for an event listener?) Either way, it has to implement \Cake\Event\EventListenerInterface. Lets say it was a standalone class and it went to src/Event/ExampleListener.php

2. Make this listener class have implementedEvents() method that looks like:

   public function implementedEvents()
   {
       return array(
           'Model.afterSave' => 'exampleAfterSave',
       );
   }

   Hooking to Model.afterSave will trigger exampleAfterSave on every model throughout your application that has this listener attached. See below on how to filter.

3. Add exampleAfterSave():

   public function exampleAfterSave($event, $entity, $options)
   {
       // Skip if triggered not on the model we need
       if ($event->getSubject()->getAlias() !== 'Users') {
           return true;
       }
       // Do something…
   }

4. Finally, the model that you would like to listen to needs to ne aware of that. In your e.g. src/Model/Table/UsersTable.php, attach the listener to the initialize() method:

   public function initialize(array $config)
   {
       //…
       $listener = new \App\ExampleCustomClasses\ExampleListener();
       $this->getEventManager()->on($listener);
   }