public static void Initialize()
        {
            Data = FileUtility.LoadUnitySceneMemoData();

            if (Data != null)
            {
                PopupWindowContent             = new UnitySceneMemoHierarchyWindow();
                EditorSceneManager.sceneSaved += (scene) => {
                    InitializeSceneMemo(scene);
                    RefreshSceneMemo(scene);
                };
                EditorSceneManager.sceneOpened += (scene, mode) => {
                    InitializeSceneMemo(scene);
                };
            }
        }
        //======================================================================
        // initialize
        //======================================================================

        public static void LoadData()
        {
            Data = FileUtility.LoadUnityEditorMemoData();
        }