Flutter manage animation controller from outside of class - flutter

Question

this is my simple animation in class witch i use that
controller = AnimationController(vsync: this, duration: Duration(milliseconds: 200));
offset = Tween<Offset>(begin: Offset.zero, end: Offset(0.0, -1.0)).animate(controller);
controller.forward();
in that i can only manage animation controller such as forward, reverse inside of class and i try to move this controller to outside of class like with another class as NotificationBarController, is any body help me how can i achieve to this solution?
for example
controller = NotificationBarController();
controller.forward();
source code
class NotificationBar extends StatefulWidget {
final Widget contentWidget;
final Widget barWidget;
NotificationBar({#required this.contentWidget, #required this.barWidget});
#override
State<StatefulWidget> createState() => NotificationBarState();
}
class NotificationBarState extends State<NotificationBar> with SingleTickerProviderStateMixin {
AnimationController controller;
Animation<Offset> offset;
#override
void initState() {
super.initState();
controller = AnimationController(vsync: this, duration: Duration(milliseconds: 200));
// offset = Tween<Offset>(begin: Offset.zero, end: Offset(1.0, 0.0)).animate(controller); from right
offset = Tween<Offset>(begin: Offset.zero, end: Offset(0.0, -1.0)).animate(controller);
controller.forward();
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Stack(
),
);
}
}
my tired class to implementing that, but this is wrong
class NotificationBarController extends ChangeNotifier {
NotificationBarController({#required TickerProvider vsync}): _animationController = AnimationController(vsync: vsync);
Animation<double> get animation => _animationController?.view ?? kAlwaysCompleteAnimation;
Animation<double> get state => _animationController?.view ?? kAlwaysCompleteAnimation;
}

Answer 1

You can use GlobalKey for it.
First you need to instantiate and store it like this
final key = GlobalKey<NotificationBarState>(), then you need to pass it to NotificationBar constructor calling super with the key. Then you can access the state and its members by calling key.currentState.someMethod().
However the whole idea doesn't look like Flutter way for me. I would suggest to subscribe to some stream or changeNotifier inside NotificationBarState and fire animation as a reaction on new event or notification