This in effect removes the direct link between event name and the method name on the handler.
Any callback can be given as a handler and the event name becomes an arbitrary string. Allowing for easier namespacing (see next commit)
The only missing part is ContainerAwareEventManager::addEventSubscriberService(),
because I'm not sure how to find out the class name of a service in the DIC.
Also, inline documentation of this code needs to be finished once it is accepted.
Doctrine's EventManager implementation has several advantages over the
EventDispatcher implementation of Symfony2. Therefore I suggest that we
use their implementation.
Advantages:
* Event Listeners are objects, not callbacks. These objects have handler
methods that have the same name as the event. This helps a lot when
reading the code and makes the code for adding an event listener shorter.
* You can create Event Subscribers, which are event listeners with an
additional getSubscribedEvents() method. The benefit here is that the
code that registers the subscriber doesn't need to know about its
implementation.
* All events are defined in static Events classes, so users of IDEs benefit
of code completion
* The communication between the dispatching class of an event and all
listeners is done through a subclass of EventArgs. This subclass can be
tailored to the type of event. A constructor, setters and getters can be
implemented that verify the validity of the data set into the object.
See examples below.
* Because each event type corresponds to an EventArgs implementation,
developers of event listeners can look up the available EventArgs methods
and benefit of code completion.
* EventArgs::stopPropagation() is more flexible and (IMO) clearer to use
than notifyUntil(). Also, it is a concept that is also used in other
event implementations
Before:
class EventListener
{
public function handle(EventInterface $event, $data) { ... }
}
$dispatcher->connect('core.request', array($listener, 'handle'));
$dispatcher->notify('core.request', new Event(...));
After (with listeners):
final class Events
{
const onCoreRequest = 'onCoreRequest';
}
class EventListener
{
public function onCoreRequest(RequestEventArgs $eventArgs) { ... }
}
$evm->addEventListener(Events::onCoreRequest, $listener);
$evm->dispatchEvent(Events::onCoreRequest, new RequestEventArgs(...));
After (with subscribers):
class EventSubscriber
{
public function onCoreRequest(RequestEventArgs $eventArgs) { ... }
public function getSubscribedEvents()
{
return Events::onCoreRequest;
}
}
$evm->addEventSubscriber($subscriber);
$evm->dispatchEvent(Events::onCoreRequest, new RequestEventArgs(...));
The three notification methods do not return the Event instance anymore.
notify() does not return anything
notifyUntil() returns the returned value of the event that has processed the event
filter() returns the filtered value
Upgrading your listeners:
Listeners for notify() and filter() events: nothing to change
Listeners for notifyUntil() events:
Before:
$event->setReturnValue('foo');
return true;
After:
$event->setProcessed();
return 'foo';
If you notify events, the processing also need to be changed:
For filter() notifications: the filtered value is now available as
the returned value of the filter() method.
For notifyUntil() notifications:
Before:
$event = $dispatcher->notifyUntil($event);
if ($event->isProcessed()) {
$ret = $event->getReturnValue();
// do something with $ret
}
After:
$ret = $dispatcher->notifyUntil($event);
if ($event->isProcessed()) {
// do something with $ret
}
* The register() method on all listeners has been removed
* Instead, the information is now put directly in the DIC tag
For instance, a listener on core.request had this method:
public function register(EventDispatcher $dispatcher, $priority = 0)
{
$dispatcher->connect('core.response', array($this, 'filter'), $priority);
}
And this tag in the DIC configuration:
<tag name="kernel.listener" />
Now, it only has the following configuration:
<tag name="kernel.listener" event="core.response" method="filter" priority="0" />
The event and method attributes are now mandatory.
