Zend framework 2: AbstractListenerAggregate - php

Question

I have a question about Zendframework 2, Event manager and listener.
class ApiErrorListener extends AbstractListenerAggregate {
public function attach(EventManagerInterface $events)
{
$this->listeners[] = $events->attach(MvcEvent::EVENT_RENDER, __CLASS__ . '::onRender', 1000);
}
public static function onRender(MvcEvent $e)
{
if($e->getResponse()->isOk())
{
return;
}
$httpCode = $e->getResponse()->getStatusCode();
$sm = $e->getApplication()->getServiceManager();
$viewModel = $e->getResult();
$exception = $viewModel->getVariable('exception');
$model = new JsonModel(
array(
'errorCode' => !empty($exception) ? $exception->getCode() : $httpCode,
'errorMsg' => !empty($exception) ? $exception->getMessage() : NULL
)
);
$model->setTerminal(true);
$e->setResult($model);
$e->setViewModel($model);
$e->getResponse()->setStatusCode($httpCode);
}
}
I think ApiErrorListener should be a listener, or say it is an observer. Why it has to implement attach() function?
Observer Design Pattern
In this link, you can see, only Subject (broadcaster attach or detach listeners).
I think I get confused ...
Anyone please help.
Thanks in advance.

Answer 1

The AbstractListenerAggregate provides functionality to attach/detachs a group of events with similar scope and purpose.
It's more of an organizational class than functionality. It provides an easy way to attach and detach events. In the case of event detaching, it provides an easy way to detach a group of events without any complicated logic to loop over ALL registered events and find the ones you're looking for.
You don't have to use the listener aggregate, you can certainly attach events to the EventManager anywhere you want in an application. However, as your application grows and there are more and more events with more and more dependencies, it can provide some sanity (AND TESTABILITY) to your event logic.