Destroying a Singleton When a Scene is Loaded

Scripting
,
1

I have a “singleton” script that is intended to run for several scenes and then end when a certain scene is loaded. I believe I have this set up to destroy the game object the singleton is a component of when build index 2 is loaded. However, it doesn’t destroy the game object until after index 2 is loaded and then exited. What am I doing wrong here?

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

public class SoundtrackSingleton : MonoBehaviour
{
    public static SoundtrackSingleton instance;
    void Awake()
    {
        ManageSingleton();
    }

    void Start()
    {
        FindObjectOfType<AudioManager>().Play("Well");
    }

    void Update()
    {
        int currentSceneIndex = SceneManager.GetActiveScene().buildIndex;
        if(currentSceneIndex == 2)
        {
            Destroy(this);
        }
    }

    void ManageSingleton()
    {
        if(instance != null)
        {
            gameObject.SetActive(false);
            Destroy(gameObject);
        }
        else
        {
            instance = this;
            DontDestroyOnLoad(gameObject);
        }
    }
}
2

You can use SceneManager.sceneLoaded instead of the Update function to get rid of the one frame delay.
You can also use DestroyImmediate instead of Destroy to make the destroying take place immediately, instead of the end of the frame.

private void Awake()
{
    if(SceneManager.GetActiveScene().buildIndex == 2 || instance != null)
    {
        gameObject.SetActive(false);
        Destroy(this);
        instance = null;
        return;
    }

    instance = this;
    DontDestroyOnLoad(gameObject);
    SceneManager.sceneLoaded += OnSceneLoaded;

    static void OnSceneLoaded(Scene scene, LoadSceneMode mode)
    {
        if(scene.buildIndex != 2)
        {
            return;
        }
     
        SceneManager.sceneLoaded -= OnSceneLoaded;

        if(instance != null)
        {
            gameObject.SetActive(false);
            Destroy(this);
            instance = null;
        }
    }
}

If the singleton really only gets destroyed only after the scene is unloaded, then you probably are using the wrong target buildIndex. Recheck your build settings.