Resolved Some objects were not cleaned up when closing the scene.

*Edit: I've resolved this. By instantiating a new instance in the Instance getter I think I was inadvertently creating new instances when the scene was closing, probably when unsubscribing from events.

I've refactored it to just initialize it in Awake().

Greetings devs,

I am getting this error in my project when I close the game:
Some objects were not cleaned up when closing the scene. (Did you spawn new GameObjects from OnDestroy?)
The following scene GameObjects were found:
ScoreManager

Here is the definition of ScoreManager:

Code (CSharp):

1. using System;
2. using UnityEngine;
3.  
4. public class ScoreManager : SingletonMonoBehavior<ScoreManager>
5. {
6.     public event Action<int> OnScoreChanged = delegate(int score) {  };
7.     public event Action<int> OnLivesChanged = delegate(int lives) {  };
8.  
9.     public int Score { get; private set; }
10.     public int Lives { get; private set; }
11.     public int Wave { get; private set; }
12.  
13.     [SerializeField] int _eggValue = 250, _extraLifeInterval = 20000;
14.  
15.     int _eggsCollected, _nextExtraLifeAt;
16.  
17.     public void ResetScore()
18.     {
19.         Wave = 1;
20.         Lives = 3;
21.         Score = 0;
22.         _eggsCollected = 0;
23.         _nextExtraLifeAt = _extraLifeInterval;
24.         OnScoreChanged(Score);
25.         OnLivesChanged(Lives);
26.     }
27.  
28.     public void AddPoints(int points)
29.     {
30.         Score += points;
31.         OnScoreChanged(Score);
32.         if (Score >= _nextExtraLifeAt)
33.         {
34.             GainLife();
35.         }
36.     }
37.  
38.     public void ScoreEgg()
39.     {
40.         AddPoints(++_eggsCollected * _eggValue);
41.     }
42.  
43.     void LoseLife()
44.     {
45.         Lives--;
46.         OnLivesChanged(Lives);
47.     }
48.  
49.     void GainLife()
50.     {
51.         Lives++;
52.         _nextExtraLifeAt += _extraLifeInterval;
53.         SoundManager.Instance.PlayFreeManSound();
54.         OnLivesChanged(Lives);
55.     }
56.  
57.     public void KillPlayer(GameObject player)
58.     {
59.         Destroy(player);
60.         LoseLife();
61.     }
62. }
63.  

As you can see it derives from SingletonMonoBehavior which is defined as follows:

Code (CSharp):

1. using UnityEngine;
2.  
3. public class SingletonMonoBehavior<T> : MonoBehaviour where T : MonoBehaviour
4. {
5.     static T _instance;
6.  
7.     public static T Instance
8.     {
9.         get
10.         {
11.             if (_instance != null) return _instance;
12.  
13.             _instance = FindObjectOfType<T>();
14.             if (_instance != null) return _instance;
15.  
16.             var singletonObject = new GameObject(typeof(T).Name);
17.             _instance = singletonObject.AddComponent<T>();
18.  
19.             return _instance;
20.         }
21.     }
22.  
23.     protected virtual void Awake()
24.     {
25.         if (Instance == null || Instance == this) return;
26.         Destroy(gameObject);
27.     }
28. }

I have another singleton in the project, SoundManager which follows the exact same pattern but I do not get an error for it.

The only difference I can see is that this class has events but I am careful to unsubscribe to those events in the only class that references them:

Code (CSharp):

1. using TMPro;
2. using UnityEngine;
3.  
4. public class ScoreboardUI : MonoBehaviour
5. {
6.     [SerializeField] TMP_Text _score;
7.     [SerializeField] Transform _playerLivesContainer;
8.     [SerializeField] GameObject _playerLifePrefab;
9.  
10.     void Start()
11.     {
12.         ScoreManager.Instance.OnScoreChanged += OnScoreChanged;
13.         ScoreManager.Instance.OnLivesChanged += OnLivesChanged;
14.     }
15.  
16.     void OnDisable()
17.     {
18.         ScoreManager.Instance.OnScoreChanged -= OnScoreChanged;
19.         ScoreManager.Instance.OnLivesChanged -= OnLivesChanged;
20.         RemoveExtraPlayerLifeIcons(0);
21.     }
22.  
23.     void OnScoreChanged(int score)
24.     {
25.         _score.text = score.ToString();
26.     }
27.  
28.     void OnLivesChanged(int lives)
29.     {
30.         var childCount = RemoveExtraPlayerLifeIcons(lives);
31.         AddMissingPlayerLifeIcons(lives, childCount);
32.     }
33.  
34.     int RemoveExtraPlayerLifeIcons(int lives)
35.     {
36.         int childCount = _playerLivesContainer.childCount;
37.         while (childCount > lives)
38.         {
39.             Destroy(_playerLivesContainer.GetChild(--childCount).gameObject);
40.         }
41.  
42.         return childCount;
43.     }
44.  
45.     void AddMissingPlayerLifeIcons(int lives, int childCount)
46.     {
47.         while (childCount < lives)
48.         {
49.             Instantiate(_playerLifePrefab, _playerLivesContainer);
50.             childCount++;
51.         }
52.     }
53. }
54.  

Here's the hierarchy where ScoreManager appears in the scene:

It seems like something is holding onto a reference to ScoreManager and keeping it from being cleaned up but darned if I can see what it is.

Any tips for diagnosing this?

Thank!