class SwipeFlowDelegate extends FlowDelegate {
  final ValueListenable<double> offsetX;
  SwipeFlowDelegate(this.offsetX) : super(repaint: offsetX);
  @override
  void paintChildren(FlowPaintingContext context) {
    Size size = context.size;
    context.paintChild(0);
    Matrix4 offsetM4 = Matrix4.translationValues(offsetX.value, 0, 0);
    context.paintChild(1, transform: offsetM4);
    // 偏移量對(duì)于父級(jí)尺寸
    if (offsetX.value == size.width) {
      Matrix4 m1 = Matrix4.translationValues(size.width / 2 - 30, size.height / 2 - 30, 0);
      context.paintChild(2, transform: m1);
      Matrix4 m2 = Matrix4.translationValues(size.width / 2 - 30, -(size.height / 2 - 50), 0);
      context.paintChild(3, transform: m2);
    }
  }
  @override
  bool shouldRepaint(covariant SwipeFlowDelegate oldDelegate) {
    return oldDelegate.offsetX.value != offsetX.value;
  }
}

final ValueNotifier<double> factor = ValueNotifier(0);
Flow(
  delegate: SwipeFlowDelegate(factor),
  children: [
    widget.content,
    widget.overflow,
    GestureDetector(
        onTap: open,
        child: const Icon(Icons.menu_open_outlined, color: Colors.white)),
    GestureDetector(
        onTap: () {
          Navigator.of(context).pop();
        },
        child: const Icon(Icons.close, color: Colors.white))
  ],
)

@override
Widget build(BuildContext context) {
  return GestureDetector(
      behavior: HitTestBehavior.opaque,
      onHorizontalDragUpdate: _onHorizontalDragUpdate,
      onHorizontalDragEnd: _onHorizontalDragEnd,
      child: SizedBox(
        height: MediaQuery.of(context).size.height,
        width: widget.width,
        child: Flow( delegate:// 同上,略...
      );
}
void _onHorizontalDragUpdate(DragUpdateDetails details) {
  double cur = factor.value + details.delta.dx;
  factor.value = cur.clamp(0, widget.width);
}
void _onHorizontalDragEnd(DragEndDetails details) {
  if (factor.value > widget.width / 2) {
    close();
  } else {
    open();
  }
}

class _ScrollHideWrapperState extends State<ScrollHideWrapper> with SingleTickerProviderStateMixin {
  late AnimationController _ctrl;
  final ValueNotifier<double> factor = ValueNotifier(0);
  @override
  void initState() {
    super.initState();
    _ctrl = AnimationController(
      duration: const Duration(milliseconds: 200),
      vsync: this,
    );
  }
  @override
  Widget build(BuildContext context) {
    // 略同...
  }
  // 動(dòng)畫關(guān)閉
  Future<void> close() async {
    Animation<double> anim = Tween<double>(begin: factor.value, end: widget.width).animate(_ctrl);
    anim.addListener(() => factor.value = anim.value);
    await _ctrl.forward(from: 0);
  }
  // 動(dòng)畫打開
  Future<void> open() async {
    Animation<double> anim = Tween<double>(begin: factor.value, end: 0).animate(_ctrl);
    anim.addListener(() => factor.value = anim.value);
    await _ctrl.forward(from: 0);
  }
}