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 $ret
}
The original HttpKernel class can be deleted, as it's request-stashing will be moved to the Kernel class. FrameworkBundle's list of compiled classes must also be modified to respect this change.
Some explanations on how it works now:
* The Session is an optional dependency of the Request. If you create the
Request yourself (which is mandatory now in the front controller) and if
you don't inject a Session yourself (which is recommended if you want the
session to be configured via dependency injection), the Symfony2 Kernel
will associate the Session configured in the Container with the Request
automatically.
* When duplicating a request, the session is shared between the parent and
the child (that's because duplicated requests are sub-requests of the main
one most of the time.) Notice that when you use ::create(), the behavior is
the same as for the constructor; no session is attached to the Request.
* Symfony2 tries hard to not create a session cookie when it is not needed
but a Session object is always available (the cookie is only created when
"something" is stored in the session.)
* Symfony2 only starts a session when:
* A session already exists in the request ($_COOKIE[session_name()] is
defined -- this is done by RequestListener);
* There is something written in the session object (the cookie will be sent
to the Client).
* Notice that reading from the session does not start the session anymore (as
we don't need to start a new session to get the default values, and because
if a session exists, it has already been started by RequestListener.)
