Flutter如何从另一个小部件访问AnimationController方法

AnimationController _controller;

@override
void initState() {
  super.initState();
  _controller = AnimationController(
    duration: Duration(seconds: 1),
    vsync: this,
  );
}

@override
Widget build(BuildContext context) {
  return ChildWidget(controller: _controller);
}

class ChildWidget extends StatelessWidget {
  final AnimationController controller;

  ChildWidget({this.controller});

  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      onPressed: () {
        controller.forward(); // 执行动画
      },
      child: Text('Start Animation'),
    );
  }
}