//----- method -----

        public RegisterScrollView()
        {
            scrollView = new FastScrollView(this);

            toolbarPlusIcon  = EditorGUIUtility.IconContent("Toolbar Plus");
            toolbarMinusIcon = EditorGUIUtility.IconContent("Toolbar Minus");

            scrollView.OnRepaintRequestAsObservable()
            .Subscribe(_ =>
            {
                if (onRepaintRequest != null)
                {
                    onRepaintRequest.OnNext(Unit.Default);
                }
            })
            .AddTo(Disposable);
        }