Does it make sense to dispatch events from another object?

Question

I'm still trying to get my head around the best way to structure event flows. Someone made a lot of sense by telling me that contained objects should be decoupled from their parent containers so they're reusable between containers. Instead of calling their parent's function, they dispatch an event. Sensible!

I recently myself in the awkward-feeling situation of dispatching an event on a contained object, from its parent. It seems more intuitive for an object to be the one dispatching its own events. Maybe I'm bordering on breaking the Law of Demeter?

Example of what I'm doing:
child.dispatchEvent(new ChildEvent(ChildEvent.IM_BEING_A_CHILD));

Am I correct in feeling strange here, or is it a normal thing for one object to dispatch another object's events?

Answer 1

You are not necessarily breaking any rules here - if dispatchEvent is a public function then you are allowed to call it from anywhere you like.

If you want to keep things cleaner from an encapsulation point of view you could instead expose an explicit function that the parent can call for a particular event to occur - eg:

child.doSomeChildAction();

and on the child class:

public function doSomeChildAction():void
{
   dispatchEvent(new ChildEvent(ChildEvent.IM_BEING_A_CHILD));
}

This way if you need to change the way child sends the event, what kind of event is sent, or what actions occur when the child sends the event it is all encapsulated in the child class, and so will be easier to manage.