Using events for communication

Hi,

I'm having a problem wrapping my head around on how should I effectively use events to decouple objects.

For example when unit is clicked few things could happen:
- ui panel should appear and display some information about the unit
- sound is played
- selection box is displayed around the unit
Etc.

So using an event where unit shouts "hey i was selected!" and listeners react to that seems like a nice way to handle this.

My biggest issue is, how should I handle adding those listeners? If I have 100 units do i add listeners for every one of those, what would be the good practice here?

One way i was thinking of handling this is using message center, where unit sends it messages to singleton object and listeners have registered to the object to receive certain types of messages. Are there any downsides in this approach i am missing?

 

All those units would be setup to send a "selection" event, the listeners then listen out for "selection" events. There would be one type of event to listen for, not 100.

 

But are listeners not setup per object instance? So each unit would have it's own set of listeners listening to events. What you are describing is more like broadcasting which I understood to be not so good practice.

What I'd love is simple way to define events ie. "Event Selected(GameObject selected)" and for objects to send and receive these events.

EDIT: So I think the question is, are UnityEvents designed for this kind of pattern? Or should I use something custom like Message Center I mentioned above?

 

I think you mean per 'instance', not per 'class'.

Well, technically, your 'singleton' is basically the same thing, and embodies other supposed "bad practices".

Of course, as long as you understand the implications of the design, it's not like it's going to kill you if you use such patterns.

Honestly, your singleton idea is 'sort of' the way I'd go.

I might not make it a Singleton... but I'd basically have a "Unit Manager" that knows about all the units, and it would forward events about if a unit is clicked or the sort. It's simple and gets the job done.

 

Cheers! I think I'll go with that approach, like you said it gets the job done and fits the way I think about the whole thing.