BuildSettingScenesUpdater.cs

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

public class BuildSettingScenesUpdater : AssetPostprocessor
{
    private const string sceneDir = "Scenes";
    private const string initialLoadScene = "Scenes/Title.unity";

    public static void OnPostprocessAllAssets(
        string[] importedAssets,
        string[] deletedAssets,
        string[] movedAssets,
        string[] movedFromAssetPaths)
    {
        if (!CheckExists())
            return;

        var assets = importedAssets
            .Union(deletedAssets)
            .Union(movedAssets)
            .Union(movedFromAssetPaths);
            
        if (CheckInSceneDir(assets))
        {
            Create();
        }
    }

    // Sceneディレクトリ以下のアセットが編集されたか
    private static bool CheckInSceneDir(IEnumerable<string> assets)
    {
        return assets.Any(asset => Path.GetDirectoryName(asset) == GetAssetsPath(sceneDir));
    }

    // 存在チェック
    private static bool CheckExists()
    {
        string sceneDirFullPath = GetFullPath(sceneDir);
        string initialLoadSceneFullPath = GetFullPath(initialLoadScene);

        if (!Directory.Exists(sceneDirFullPath))
        {
            Debug.LogError("Not Found Dir :" + sceneDirFullPath);
            return false;
        }

        if (!File.Exists(initialLoadSceneFullPath))
        {
            Debug.LogError("Not Found Inital Load Scene : " + initialLoadSceneFullPath);
            return false;
        }

        return true;
    }

    private static void Create()
    {
        string sceneDirAssetsPath = GetAssetsPath(sceneDir);
        string initialLoadSceneAssetsPath = GetAssetsPath(initialLoadScene);

        var scenes = AssetDatabase.FindAssets("t:Scene", new string[] {sceneDirAssetsPath})
            .Select(guid => AssetDatabase.GUIDToAssetPath(guid))
            .OrderBy(path => path)
            .Where(path => path != initialLoadSceneAssetsPath)
            .Select(path => new EditorBuildSettingsScene(path, true))
            .ToList();

        // 初回に呼び込まれて欲しいシーンを先頭に配置する
        scenes.Insert(0, new EditorBuildSettingsScene(initialLoadSceneAssetsPath, true));

        EditorBuildSettings.scenes = scenes.ToArray();
        AssetDatabase.SaveAssets();

        Debug.Log("Created BuildSettings.");
    }

    private static string GetFullPath(string path)
    {
        return Application.dataPath + "/" + path;
    }

    private static string GetAssetsPath(string path)
    {
        return "Assets/" + path;
    }
}