问返回页面后恢复AnimationController状态

EN

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return 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 Counter extends StatefulWidget {
  State createState() => new _CounterState();
}

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

  static const int startCount = 10;

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

  @override
  Widget build(BuildContext context) {
    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: startCount,
              end: 0,
            ).animate(_controller),
          ),
        ),
      ),
    );
  }
}