When to unsubscribe from Event?

Hi,

I am trying to understand when to Unsubscribe/unregister from an event? it seems you can controll when the observer receives notifications by subscribing in the OnEnabled/OnDisabled. Would I unregister whenever the object is destroyed/disabled, and is there any other time I would need to unregister from teh event besides object destroyed or disabled/notActive?

 

OnDisable works fine. It fires when both destroyed and disabled.

Only if you don't want to know about the event anymore.

 

Another potential pitfall is when a method subscribes to an event. If you do not unsubscribe first, then you could end up with multiple callbacks when that event is triggered. That can get messy.

 

not entirely sure what you mean sorry. I thought methods always subscribed to an event? do you have an example if you have time? Im having an aha moment with coding and a lot of crap is being tied together right now including this lol.

 

Here, test it you'll understand it easily.

Put this in scene

Code (CSharp):

1. using System;
2. using UnityEngine;
3.  
4. public class Foob : MonoBehaviour
5. {
6.     public static EventHandler StuffDone;
7.  
8.     private void Update()
9.     {
10.         if (Input.GetKeyDown(KeyCode.Space))
11.         {
12.             StuffDone?.Invoke(this, EventArgs.Empty);
13.         }
14.     }
15. }

Then put this on another object

Code (CSharp):

1. using UnityEngine;
2.  
3. public class Bar : MonoBehaviour
4. {
5.     private void OnEnable()
6.     {
7.         Foob.StuffDone += OnStuffDone;
8.     }
9.  
10.     private void OnStuffDone(object sender, System.EventArgs e)
11.     {
12.         Debug.Log("Fubar");
13.     }
14. }

Press space. OnStuffDone is called once on "Bar".

Disable bar and re-enable it, then press space again. It'll be called twice this time, and so on.

That being said, you're safe with subbing in OnEnable and unsubbing on OnDisable. Personally I never ran into an issue or heard of anybody having one with this.

 

I mean methods that can be used multiple times.