Dispatcher Events

Until now the focus was on the MVC layer of a component using com_acme as an example. For each MVC triad there are twenty-two plugin events that get broadcast via the Event API.

However, there are another twenty-two plugin events that a plugin can tap into. Each component has a dispatcher. The dispatcher acts as a component front controller. It routes the request to the correct controller, which then handles it form there.

The abstract dispatcher KDispatcherAbstract has four action methods:

method description
_actionDispatch Loads the controller and executing the right action on the controller.
_actionForward Handles the redrection of a request after the dispatch method has done its work
_actionFail Prepares an Exception response for the client
_actionSend Used to send the response to the client

The HTTP dispatcher KDispatcherHttp adds seven more actions which correspond to the HTTP methods:

method description
_actionHead Respond to request with headers only
_actionOptions Respond with HTTP verbs allowed by controller for the authenticated user
_actionGet Execute the GET request against the right controller
_actionPost Interpret the POST request to determine the right non-safe action to take, i.e. add, edit, delete
_actionPut Results in an add or edit action being called on the controller.
_actionDelete Handles the request made with DELETE HTTP method. Will execute delete on the controller.
_actionRedirect Handles redirection after dispatching is complete, of if called from another dispatcher method

PlgAcmeExample with a Dispatcher Event Handler

Your plugin can control how any Joomlatools component handles the actions described above. A few example uses:

  • component wide access control
  • HTTP method restriction
  • request logging
  • override all controller redirects

You should use the dispatcher event handlers only when you want to effect a component when it's being dispatched. If you wish to intercept an event for a specific entity, use one of the MVC event handlers.

Here is the PlgAcmeExample with a new event handler. It checks that any POST request coming into com_acme has a foo variable before allowing the dispatcher to continue.

class PlgAcmeExample extends PlgKoowaSubscriber
    function onBeforeAcmeDispatcherPost(KEventInterface $event)
        if(!$event->getSubject()->getRequest()->foo) {
            JFactory::getApplication()->redirect('/', 'You have no Foo!');  

Note: The naming convention is close to the MVC listeners, but there is no entity:

on + [Before] + [Acme] + [Dispatcher] + [Post]