ScenelistWindow.cs

using System.Collections.Generic;
using System.IO;
using System.Linq;
using UnityEditor;
using UnityEngine;

public struct SceneInfo
{
    public string FolderName;
    public string SceneName;
    public string ScenePath;
}

public class ScenelistWindow : EditorWindow
{
    ScenenlistSerializeable instance;

    private Vector2 _scrollPosition;
    private static readonly string RootFolder = "Assets";
    private readonly List<SceneInfo> Scenes = new List<SceneInfo>();
    List<string> OnlySceneNames = new List<string>();

    int QuickSwitch1SceneListID = 0;
    int QuickSwitch2SceneListID = 0;
    bool dropDownSceneList = false;

    string scriptFolderDataPath = "";

    [MenuItem("Window/ShowScenes")]
    public static void Init()
    {
        GetWindow(typeof(ScenelistWindow), false, "Scenes");
    }

    string m_ScriptFilePath;
    string m_ScriptFolder;
    string GetScriptAssetPath()
    {
        var tmpInstance = CreateInstance<ScenenlistSerializeable>();
        MonoScript ms = MonoScript.FromScriptableObject(tmpInstance);
        m_ScriptFilePath = AssetDatabase.GetAssetPath(ms);

        //FileInfo fi = new FileInfo(m_ScriptFilePath);
        //m_ScriptFolder = fi.Directory.ToString();
        //m_ScriptFolder.Replace('\\', '/');

        // Asset/.../Folder
        return m_ScriptFilePath.Substring(0, m_ScriptFilePath.LastIndexOf("/"));
    }

    void OnEnable()
    {
        LoadData();
        SearchForScenes();
    }

    void OnDisable()
    {
        SaveData();
    }

    void LoadData()
    {

        scriptFolderDataPath = GetScriptAssetPath() + "/ScenenlistData.asset";
        instance = AssetDatabase.LoadAssetAtPath<ScenenlistSerializeable>(scriptFolderDataPath);
        if(instance == null) {
            instance = CreateInstance<ScenenlistSerializeable>();
            EditorUtility.SetDirty(instance);
            AssetDatabase.CreateAsset(instance, scriptFolderDataPath);
            AssetDatabase.SaveAssets();
            AssetDatabase.Refresh();
        }
        else {
            QuickSwitch1SceneListID = instance.QuickSwitch1ID;
            QuickSwitch2SceneListID = instance.QuickSwitch2ID;
        }
    }

    void SaveData()
    {
        if(instance) {
            EditorUtility.SetDirty(instance);
            instance.QuickSwitch1ID = QuickSwitch1SceneListID;
            instance.QuickSwitch2ID = QuickSwitch2SceneListID;
            AssetDatabase.SaveAssets();
            AssetDatabase.Refresh();
        }
    }

    private void OnGUI()
    {
        if(GUILayout.Button("Research Scenes")) {
            SearchForScenes();
        }

        GUILayout.Space(10f);

        GUILayout.BeginHorizontal();
        GUILayout.Label("Quick switch 1");
        QuickSwitch1SceneListID = EditorGUILayout.Popup(QuickSwitch1SceneListID, OnlySceneNames.ToArray());

        if(GUILayout.Button("Switch", GUILayout.MaxHeight(14f), GUILayout.MaxWidth(100f)))
            OpenScene(QuickSwitch1SceneListID);

        GUILayout.EndHorizontal();

        GUILayout.Space(2f);

        GUILayout.BeginHorizontal();
        GUILayout.Label("Quick switch 2");
        QuickSwitch2SceneListID = EditorGUILayout.Popup(QuickSwitch2SceneListID, OnlySceneNames.ToArray());

        if(GUILayout.Button("Switch", GUILayout.MaxHeight(14f), GUILayout.MaxWidth(100f)))
            OpenScene(QuickSwitch2SceneListID);
        GUILayout.EndHorizontal();

        GUILayout.Space(10f);

        if(!dropDownSceneList) {
            if(GUILayout.Button("Show Scenes"))
                dropDownSceneList = true;
        }
        else {
            if(GUILayout.Button("Hide Scenes"))
                dropDownSceneList = false;

            _scrollPosition = GUILayout.BeginScrollView(_scrollPosition, GUILayout.Height(position.height / 1.8f));

            string lastDir = "";
            for(int i = 0; i < Scenes.Count; i++) {

                var scene = Scenes[i];

                if(lastDir != scene.FolderName) {
                    lastDir = scene.FolderName;
                    GUILayout.Space(10);
                    GUILayout.Label(lastDir);
                }

                if(GUILayout.Button(scene.SceneName))
                    OpenScene(i);
            }
            GUILayout.EndScrollView();
        }
    }

    void OpenScene(int id)
    {
        if(EditorApplication.SaveCurrentSceneIfUserWantsTo())
            EditorApplication.OpenScene(Scenes[id].ScenePath);
    }

    void SearchForScenes()
    {
        OnlySceneNames.Clear();
        Scenes.Clear();
        ProcessDirectory(RootFolder);
    }

    void ProcessDirectory(string targetDirectory)
    {
        // Process the list of files found in the directory.
        string[] fileEntries = Directory.GetFiles(targetDirectory);
        foreach(string fileName in fileEntries)
            ProcessFile(fileName, targetDirectory);

        // Recurse into subdirectories of this directory.
        string[] subdirectoryEntries = Directory.GetDirectories(targetDirectory);
        foreach(string subdirectory in subdirectoryEntries)
            ProcessDirectory(subdirectory);
    }

    // Insert logic for processing found files here.
    void ProcessFile(string fileName, string folderName)
    {
        if(!fileName.Contains(".unity") || fileName.Contains(".meta")) return;
        var name = fileName.Substring(fileName.LastIndexOf('\\') + 1);
        name = name.Substring(0, name.Length - 6);
        var sceneInfo = new SceneInfo {
            SceneName = name,
            ScenePath = fileName,
            FolderName = folderName
        };
        Scenes.Add(sceneInfo);
        OnlySceneNames.Add(sceneInfo.SceneName);
    }
}