我看到很多人说 Symfony2、Zend Framework 2 和其他人是事件驱动的。

在桌面世界中，通过事件驱动编程，我理解应用程序会在其状态发生变化时通知其观察者。

由于 PHP 应用程序是无状态的，因此无法做这样的事情。 IE。当用户使用界面时，将观察者绑定(bind)到观察变化的 View 。相反，它需要一个新的请求过程来更新 View 。所以，这不是一个事件，而是一个全新的请求 .

另一方面，还有一个类似的概念:事件驱动架构。

在这里，您可以阅读两者:

http://en.wikipedia.org/wiki/Event-driven_programming

http://en.wikipedia.org/wiki/Event-driven_architecture

这是另一个:

http://en.wikipedia.org/wiki/Signal_programming

A signal is a notification to a process that an event occurred. Signals are sometimes described as software interrupts. Signals are analogous to hardware interrupts in that they interrupt the normal flow of execution of a program; in most cases, it is not possible to predict exactly when a signal will arrive.

• Stackoverflow [singals] tag description

The article about AOP I've linked above ( http://mwop.net/blog/251-Aspects,-Filters,-and-Signals,-Oh,-My!.html ) was written by Matthew Weier O'Phinney (ZF Leader). IIRC, it doesn't have mentions about "event-driven", just signal and slots.

The Symfony2 EventDispatcher component description doesn't have mentions about being for "event-driven" applications: http://symfony.com/doc/current/components/event_dispatcher/introduction.html It only contains references to "Events" (which, indeed, are handled by Signal and Slots).

最佳答案

Disclaimer: It's a long answer, but I think it's worth the read with all its references. And IMHO it leads to a conclusive answer.

Event-driven !== Request-driven

"[...] I find this the most interesting difference in event collaboration, to paraphrase Jon Udell: request driven software speaks when spoken to, event driven software speaks when it has something to say.

A consequence of this is that the responsibility of managing state shifts. In request collaboration you strive to ensure that every piece of data has one home, and you look it up from that home if you want it. This home is responsible for the structure of data, how long it's stored, how to access it. In the event collaboration scenario the source of new data is welcome to forget the data the second it's passed to its Message Endpoint."

Martin Fowler - Event Collaboration (Queries section)

We are used to dividing programs into multiple components that collaborate together. (I'm using the vague 'component' word here deliberately since in this context I mean many things: including objects within a program and multiple processes communicating across a network.) The most common way of making them collaborate is a request/response style. If a customer object wants some data from a salesman object, it invokes a method on the salesman object to ask it for that data.

Another style of collaboration is Event Collaboration. In this style you never have one component asking another to do anything, instead each component signals an event when anything changes. Other components listen to that event and react however they wish to. The well-known observer pattern is an example of Event Collaboration.

Martin Fowler - Focus on events (section: Using events to collaborate)

Note: Although, it can be adapted to be event-driven

class MvcEvent extends Event
{
    /**#@+
     * Mvc events triggered by eventmanager
     */
    const EVENT_BOOTSTRAP      = 'bootstrap';
    const EVENT_DISPATCH       = 'dispatch';
    const EVENT_DISPATCH_ERROR = 'dispatch.error';
    const EVENT_FINISH         = 'finish';
    const EVENT_RENDER         = 'render';
    const EVENT_ROUTE          = 'route';

    // [...]
}

/**
 * Run the application
 *
 * @triggers route(MvcEvent)
 *           Routes the request, and sets the RouteMatch object in the event.
 * @triggers dispatch(MvcEvent)
 *           Dispatches a request, using the discovered RouteMatch and
 *           provided request.
 * @triggers dispatch.error(MvcEvent)
 *           On errors (controller not found, action not supported, etc.),
 *           populates the event with information about the error type,
 *           discovered controller, and controller class (if known).
 *           Typically, a handler should return a populated Response object
 *           that can be returned immediately.
 * @return ResponseInterface
 */
public function run()
{
    $events = $this->getEventManager();
    $event  = $this->getMvcEvent();

    // Define callback used to determine whether or not to short-circuit
    $shortCircuit = function ($r) use ($event) {
        if ($r instanceof ResponseInterface) {
            return true;
        }
        if ($event->getError()) {
            return true;
        }
        return false;
    };

    // Trigger route event
    $result = $events->trigger(MvcEvent::EVENT_ROUTE, $event, $shortCircuit);
    if ($result->stopped()) {
        $response = $result->last();
        if ($response instanceof ResponseInterface) {
            $event->setTarget($this);
            $events->trigger(MvcEvent::EVENT_FINISH, $event);
            return $response;
        }
        if ($event->getError()) {
            return $this->completeRequest($event);
        }
        return $event->getResponse();
    }
    if ($event->getError()) {
        return $this->completeRequest($event);
    }

    // Trigger dispatch event
    $result = $events->trigger(MvcEvent::EVENT_DISPATCH, $event, $shortCircuit);

    // Complete response
    $response = $result->last();
    if ($response instanceof ResponseInterface) {
        $event->setTarget($this);
        $events->trigger(MvcEvent::EVENT_FINISH, $event);
        return $response;
    }

    $response = $this->getResponse();
    $event->setResponse($response);

    return $this->completeRequest($event);
}

// albums controller
public function indexAction()
{
    return new ViewModel(array(
        'albums' => $this->albumsService->getAlbumsFromArtist('Joy Division'),
    ));
}

/**
 * Handles a request to convert it to a response.
 *
 * Exceptions are not caught.
 *
 * @param Request $request A Request instance
 * @param integer $type    The type of the request (one of HttpKernelInterface::MASTER_REQUEST or HttpKernelInterface::SUB_REQUEST)
 *
 * @return Response A Response instance
 *
 * @throws \LogicException If one of the listener does not behave as expected
 * @throws NotFoundHttpException When controller cannot be found
 */
private function handleRaw(Request $request, $type = self::MASTER_REQUEST)
{
    // request
    $event = new GetResponseEvent($this, $request, $type);
    $this->dispatcher->dispatch(KernelEvents::REQUEST, $event);

    if ($event->hasResponse()) {
        return $this->filterResponse($event->getResponse(), $request, $type);
    }

    // load controller
    if (false === $controller = $this->resolver->getController($request)) {
        throw new NotFoundHttpException(sprintf('Unable to find the controller for path "%s". Maybe you forgot to add the matching route in your routing configuration?', $request->getPathInfo()));
    }

    $event = new FilterControllerEvent($this, $controller, $request, $type);
    $this->dispatcher->dispatch(KernelEvents::CONTROLLER, $event);
    $controller = $event->getController();

    // controller arguments
    $arguments = $this->resolver->getArguments($request, $controller);

    // call controller
    $response = call_user_func_array($controller, $arguments);

    // view
    if (!$response instanceof Response) {
        $event = new GetResponseForControllerResultEvent($this, $request, $type, $response);
        $this->dispatcher->dispatch(KernelEvents::VIEW, $event);

        if ($event->hasResponse()) {
            $response = $event->getResponse();
        }

        if (!$response instanceof Response) {
            $msg = sprintf('The controller must return a response (%s given).', $this->varToString($response));

            // the user may have forgotten to return something
            if (null === $response) {
                $msg .= ' Did you forget to add a return statement somewhere in your controller?';
            }
            throw new \LogicException($msg);
        }
    }

    return $this->filterResponse($response, $request, $type);
}

    // Trigger dispatch event
    $result = $events->trigger(MvcEvent::EVENT_DISPATCH, $event, $shortCircuit);

class NewUser extends TPage
{
    /**
     * Checks whether the username exists in the database.
     * This method responds to the OnServerValidate event of username's custom validator.
     * @param mixed event sender
     * @param mixed event parameter
     */
    public function checkUsername($sender,$param)
    {
        // valid if the username is not found in the database
        $param->IsValid=UserRecord::finder()->findByPk($this->Username->Text)===null;
    }
    [...]
}

关于PHP:我是否将事件驱动编程与信号感知接口(interface)(信号和插槽/观察者模式)混为一谈？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/12232874/