Restore AnimationController State Upon returning to Page

// Context: https://stackoverflow.com/questions/58775671/restore-animationcontroller-state-upon-returning-to-page

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Provider<CounterStateModel>(
      builder: (context) => CounterStateModel(),
      child: MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: MyHomePage(title: 'Flutter Demo Home Page'),
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            FlatButton(
              color: Colors.blue,
              child: Text("AnimatonController"),
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => Counter()),
                );
              },
            ),
          ],
        ),
      ),
    );
  }
}

class CounterText extends AnimatedWidget {
  CounterText({Key key, this.animation})
      : super(key: key, listenable: animation);
  Animation<int> animation;

  @override
  build(BuildContext context) {
    return new Text(
      animation.value.toString(),
      style: new TextStyle(fontSize: 200.0),
    );
  }
}

class CounterStateModel {
  AnimationController _controller;
  int startCount = 10;
}

class Counter extends StatefulWidget {
  State createState() => new _CounterState();
}

class _CounterState extends State<Counter> with TickerProviderStateMixin {
  AnimationController _controller;

  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    CounterStateModel _counterStateModel =
        Provider.of<CounterStateModel>(context);
    if (_counterStateModel._controller == null) {
      _counterStateModel._controller = new AnimationController(
        vsync: this,
        duration: new Duration(seconds: _counterStateModel.startCount),
      );
      _counterStateModel._controller = _controller;
    } else {
      _controller = _counterStateModel._controller;
    }
    return new Scaffold(
      floatingActionButton: new FloatingActionButton(
          child: Icon(_controller.isAnimating ? Icons.pause : Icons.play_arrow),
          onPressed: () {
            setState(() {
              _controller.isAnimating
                  ? _controller.stop()
                  : _controller.forward();
            });
          }),
      body: new Container(
        child: new Center(
          child: new CounterText(
            animation: new StepTween(
              begin: _counterStateModel.startCount,
              end: 0,
            ).animate(_controller),
          ),
        ),
      ),
    );
  }
}