Flutter-CustomPainter总是在更改通知时重新绘画两个画家

Question

我有一个CustomPainter，它具有一个更复杂的绘画工具（alot文本）和一个更轻量级的foregroundpainter，可以绘制一个小的突出显示框。

每当突出显示发生变化并调用notifyListeners时，两者都会重新绘制。

为什么会这样，如何避免呢？ 我还尝试了带有两个CustomPaint的Stack，结果相同。

class NotationPlayerWidget extends StatefulWidget {
  @override
  NotationPlayerState createState() => NotationPlayerState();
}

class NotationPlayerState extends StatefulWidget<NotationPlayerWidget> {

  NotationPainter _notationPainter;
  HighlightPainter _highlightPainter;

  ScrollController _scrollController = ScrollController();


  update(Offset pos) {
    _highlightPainter.offset = offset;
    _highlightPainter.notifyListeners();
  }


  @override
  Widget build(BuildContext context) {

    if(_notationPainter == null) _notationPainter = NotationPainter();
    if(_highlightPainter == null) _highlightPainter = HighlightPainter();

    return SingleChildScrollView(
      controller: _scrollController,
      child: FittedBox(
        fit: BoxFit.fitWidth,
        child: CustomPaint(size: CanvasUtil.calcSize(song),
            painter: _notationPainter,
            foregroundPainter: _highlightPainter,
        ),
      )
    );
  }
}

class HighlightPainter extends CustomPainter with ChangeNotifier{
  HighlightPainter() ;

  Offset offset = Offset(0,0);


  @override
  void paint(Canvas canvas, Size size) {
    print("repaint highlight");

    //paint stuff
  }


  @override
  bool shouldRepaint(HighlightPainter old) {
    false;
  }
}

class NotationPainter extends CustomPainter with ChangeNotifier{
  NotationPainter() ;

  @override
  void paint(Canvas canvas, Size size) {
    print("repaint notation");

    //paint stuff
  }


  @override
  bool shouldRepaint(HighlightPainter old) {
    false;
  }
}