flutter创建可移动的stack小部件

class HomeView extends StatefulWidget {
  @override
  _HomeViewState createState() => _HomeViewState();
}
class _HomeViewState extends State<HomeView> {
  List<Widget> movableItems = [];
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Stack(
          children: movableItems,
        ));
  }
}

class _MoveableStackItemState extends State<MoveableStackItem> {
  double xPosition = 0;
  double yPosition = 0;
  Color color;
  @override
  void initState() {
    color = RandomColor().randomColor();
    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    return Positioned(
      top: yPosition,
      left: xPosition,
      child: GestureDetector(
        onPanUpdate: (tapInfo) {
          setState(() {
            xPosition += tapInfo.delta.dx;
            yPosition += tapInfo.delta.dy;
          });
        },
        child: Container(
          width: 150,
          height: 150,
          color: color,
        ),
      ),
    );
  }
}

 return Scaffold(
  floatingActionButton: FloatingActionButton(
    onPressed: () {
      setState(() {
        movableItems.add(MoveableStackItem());
      });
    },
  ),
  body: Stack(
    children: movableItems,
  ));