Zend Framework 2: preDispatch(), returning properly without executing action

Getting ZF2 to do preDispatch() and postDispatch() like ZF1 had is widely known and documented. In your controller, add this:

protected function attachDefaultListeners()
{
    parent::attachDefaultListeners();

    $event_mgr = $this->getEventManager();
    $event_mgr->attach('dispatch', array($this, 'preDispatch'), 100);
    $event_mgr->attach('dispatch', array($this, 'postDispatch'), -100);
}

Two simple listeners are attached with proper priorities to trigger before and after the action.

However, to go somewhere else before the action is executed adds some complexity, as one can expect. In preDispatch() you can do one of two suggested things. A redirect:

// Do a HTTP/302 redirect
return $this->redirect()->toRoute(
    'application', array('controller' => 'index', 'action' => 'index'
));

My issue here is, that it literally does a HTTP/302 redirect in your browser. Another problem is, that it still executes the action it was targeted to. It renders the view, runs all the listeners, does all the plugins and helpers as it started to do. It just redirects after all that. I don't want my user to do a redirect or to run all the bells and whistles including the action. Why cannot I simply return something else instead, like ZF1 could be programmed to do. On my top-1 list is to execute an action from another controller?

So, the another option to do is to simply call it quits right in the middle of preDispatch():

$url = $event->getRouter()
             ->assemble(
                   array('action' => 'index'),
                   array('name' => 'frontend')
               );

$response = $event->getResponse();
$response->getHeaders()->addHeaderLine('Location', $url);
$response->setStatusCode(302);
$response->sendHeaders();
exit();

That's pretty much the same as previous, but uglier. exit()!! Really? In Zend Framework?! I'd rather keep the wheels rolling and machine turning like it normally would do until it has done all the dirty deeds it wants to do. Poking around The Net reveals, that nobody is really offering anything else. Apparently everybody simply are doing a copy/paste from the same sites I found.

This is what I offer. Discard the current operation, start a new one and return that! A lot better alternative.

Example 1, return JSON-data:

$event->stopPropagation(true);
// Skip executing the action requested. Return this instead.
$result = new JsonModel(array(
                'success' => false,
                'loginrequired' => true
            ));
$result->setTerminal(true);
$event->setResponse(new Response());
$event->setViewModel($result);

The key is in the setResponse()-call.

Example 2, call another action:

$event->stopPropagation(true);
// Skip executing the action requested.
// Execute anotherController::errorAction() instead.
$event->setResponse(new Response());
$result = $this->forward()->dispatch('Another', array(
                'action' => 'error'
));
$result->setTerminal(true);
$event->setViewModel($result);

Hope this helps somebody else trying to do a ZF1 to ZF2 transition. In the end, there is only one thing similar between them. Their name has Zend Framwork in it.