Animator Widget

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  bool _selected = false;

  void _incrementCounter() {
    setState(() {
      _selected = !_selected;
    });
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: Animator(
        title: widget.title,
        selected: _selected,
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class Animator extends StatefulWidget {
  final String title;
  final bool selected;

  const Animator({Key key, @required this.title, @required this.selected})
      : super(key: key);

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

class _AnimatorState extends State<Animator>
    with SingleTickerProviderStateMixin<Animator> {
  AnimationController _controller;
  Animation _animation;

  @override
  void initState() {
    _controller =
        AnimationController(vsync: this, duration: Duration(milliseconds: 500));
    _animation =
        ColorTween(begin: Colors.white, end: Colors.red).animate(_controller);
    super.initState();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  void didUpdateWidget(Animator oldWidget) {
    super.didUpdateWidget(oldWidget);

    if (oldWidget.selected != widget.selected) {
      if (widget.selected) {
        _controller.forward();
      } else {
        _controller.reverse();
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: _controller,
      builder: (context, child) {
        print('${_animation.value}');
        return Container(
          color: _animation.value,
          child: Center(
            child: Text(widget.title),
          ),
        );
      },
    );
  }
}