Does an UnityEvent prevent Garbage Collection?

Questions & Answers
1

Having the following script:

public class Code : MonoBehaviour
{
    public UnityEvent MyEvent = new UnityEvent();
    public static Code Instance;
    
    void OnEnable()
    {
        Instance = this;
    }
}

Another separate object subscribes to the Event created and destroys itself without unsubscribing from the Event:

public class Player : MonoBehaviour
{
    void Start()
    {
        Code.Instance.MyEvent.AddListener(OnCall);
        Destroy(gameObject);
    }

    void OnCall()
    {
        Debug.Log("Called");
    }

 }

Will the event, that is holding a pointer to the object, prevent the garbage collection and release of memory from the destroyed object?

2

Yes, it would hold the managed part of the class in memory. So if you Destroy() the gameobject that contained the monobehaviour with the method you added as listener, the monobehaviour will be destroyed in the engine itself, but it’s native counterpart will still exist. The class will from now on “pretend” it’s null because its native part is missing. No Unity callbacks will be called on that class once it’s destroyed, but you can still invoke any method manually. That includes a delegate to which the class is still subscribed.

To prevent that you might want to implement an OnDestroy method which is called when the class is destroyed. There you can unsubscribe from the event.