immutable_dispatcher.rst

.. index::
    single: Event Dispatcher; Immutable

The Immutable Event Dispatcher

.. versionadded:: 2.1
    This feature was added in Symfony 2.1.

The :class:`Symfony\\Component\\EventDispatcher\\ImmutableEventDispatcher` is a locked or frozen event dispatcher. The dispatcher cannot register new listeners or subscribers.

The ImmutableEventDispatcher takes another event dispatcher with all the listeners and subscribers. The immutable dispatcher is just a proxy of this original dispatcher.

To use it, first create a normal dispatcher (EventDispatcher or ContainerAwareEventDispatcher) and register some listeners or subscribers:

use Symfony\Component\EventDispatcher\EventDispatcher;

$dispatcher = new EventDispatcher();
$dispatcher->addListener('foo.action', function ($event) {
    // ...
});

// ...

Now, inject that into an ImmutableEventDispatcher:

use Symfony\Component\EventDispatcher\ImmutableEventDispatcher;
// ...

$immutableDispatcher = new ImmutableEventDispatcher($dispatcher);

You'll need to use this new dispatcher in your project.

If you are trying to execute one of the methods which modifies the dispatcher (e.g. addListener), a BadMethodCallException is thrown.