Scene Loader

SceneHelpers.cs

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


public static class SceneHelpers
{
    public static string[] GetValidSceneNames()
    {
        int sceneCount = SceneManager.sceneCountInBuildSettings;
        var scenes = new string[sceneCount];
        for (int i = 0; i < sceneCount; i++)
            scenes[i] = Path.GetFileNameWithoutExtension(SceneUtility.GetScenePathByBuildIndex(i));
        return scenes;
    }

    public static Dictionary<string, int> GetSceneNameToBuildIndexMap()
    {
        int sceneCount = SceneManager.sceneCountInBuildSettings;
        Dictionary<string, int> result = new Dictionary<string, int>();
        for (int i = 0; i < sceneCount; i++)
            result.Add(Path.GetFileNameWithoutExtension(SceneUtility.GetScenePathByBuildIndex(i)), i);             
        return result;
    }
}

SceneLoader.cs

using System.Collections;
using System.Collections.Generic;
using DG.Tweening;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;

public class SceneLoader : MonoBehaviour
{
    public float fadeOutTime = 2;
    public float fadeInTime = 2;
    public Image fadeImage;

    private Contexts _contexts;
    private Scene _rootScene;
    private readonly HashSet<string> _validScenes = new HashSet<string>();
    
    public static SceneLoader Instance;

    void Awake()
    {
        Instance = this;
        DontDestroyOnLoad(gameObject);
        _rootScene = SceneManager.GetActiveScene();
        _validScenes.AddRange(SceneHelpers.GetValidSceneNames());
        InitializeScene(_rootScene);
    }

    private void InitializeScene(Scene scene)
    {
        // scene initialization code here        
        
        foreach (var rootGameObject in scene.GetRootGameObjects())
        {
            // gameobject initialization
        }
    }

    public void LoadScene(string sceneName, bool unloadExisting)
    {
        if (!_validScenes.Contains(sceneName)) throw new Exception(string.Format("Scene {0} is not defined in build settings"), sceneName);
        StartCoroutine(SwitchScenes(sceneName, unloadExisting));
    }

    private IEnumerator SwitchScenes(string newScene, bool unloadExisting)
    {
        if (unloadExisting)
        {
            var unloadTarget = SceneManager.GetActiveScene();
            if (fadeImage != null)
            {
                var fadeOut = DOTween.Sequence();
                fadeOut.SetEase(Ease.Linear);
                fadeOut.Append(fadeImage.DOFade(1, fadeOutTime));
                fadeOut.Play();
                while (fadeOut.IsPlaying()) yield return null;
            }
            if (unloadTarget != null) 
            {
                var unload = SceneManager.UnloadSceneAsync(unloadTarget);
                while (!unload.isDone) yield return null;            
            }
        }

        var loadTarget = "Scenes/" + newScene;
        var load = SceneManager.LoadSceneAsync(loadTarget, LoadSceneMode.Additive);
        while (!load.isDone) yield return null;

        var newSceneReference = SceneManager.GetSceneByName(newScene);
        SceneManager.SetActiveScene(newSceneReference);
        InitializeScene(newSceneReference);

        if (fadeImage == null) yield break;
        var fadeIn = DOTween.Sequence();
        fadeIn.SetEase(Ease.Linear);
        fadeIn.Append(fadeImage.DOFade(0, fadeInTime));
        fadeIn.Play();
    }
}