[Part 5] Some objects were not cleaned up when closing the scene

[Terence]

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@calymv3686 asks this question on YouTube:

The problem I got is when I stop the game I will get a gem on the map and an Error in Unity Some objects were not cleaned up when closing the scene. (Did you spawn new GameObjects from OnDestroy?) The following scene GameObjects were found: Blue Gem(Clone)

And the resolve was

private bool isQuitting = false;

private void OnApplicationQuit() {
    isQuitting = true;
}
 if (isQuitting) return;

[Terence]

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As the error message reveals, the issue is caused by OnDestroy() on DropRateManager spawning new GameObjects (see highlighted part below), as Unity is unable to destroy them when quitting:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class DropRateManager : MonoBehaviour
{
    [System.Serializable]   //Serialize the class
    public class Drops
    {
        public string name;
        public GameObject itemPrefab;
        public float dropRate;
    }

    public List<Drops> drops;

    void OnDestroy()
    {
        float randomNumber = UnityEngine.Random.Range(0f, 100f);
        List<Drops> possibleDrops = new List<Drops>();

        foreach (Drops rate in drops)
        {
            if (randomNumber <= rate.dropRate)
            {
                possibleDrops.Add(rate);
            }
        }
        //Check if there are possible drops
        if(possibleDrops.Count > 0)
        {
            Drops drops = possibleDrops[UnityEngine.Random.Range(0, possibleDrops.Count)];
            Instantiate(drops.itemPrefab, transform.position, Quaternion.identity);
        }
    }
}

To fix this, you will need to track if the application is quitting, and prevent the creation of new GameObjects by OnDestroy() if so:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class DropRateManager : MonoBehaviour
{
    [System.Serializable]   //Serialize the class
    public class Drops
    {
        public string name;
        public GameObject itemPrefab;
        public float dropRate;
    }

    public List<Drops> drops;
    bool isQuitting = false;

    void OnApplicationQuit() { isQuitting = true; }

    void OnDestroy()
    {
        if(isQuitting) return;
        float randomNumber = UnityEngine.Random.Range(0f, 100f);
        List<Drops> possibleDrops = new List<Drops>();

        foreach (Drops rate in drops)
        {
            if (randomNumber <= rate.dropRate)
            {
                possibleDrops.Add(rate);
            }
        }
        //Check if there are possible drops
        if(possibleDrops.Count > 0)
        {
            Drops drops = possibleDrops[UnityEngine.Random.Range(0, possibleDrops.Count)];
            Instantiate(drops.itemPrefab, transform.position, Quaternion.identity);
        }
    }
}

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