AnimatedWidget demo

animation.dart

import 'package:flutter/material.dart';
import 'radial_logo.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,
        accentColor: Colors.red,
        brightness: Brightness.light,
      ),
      home: Scaffold(
          appBar: AppBar(
            title: Text('Flutter Demo')
          ),
          body: AnimationExample()
      )
    );
  }
}


class AnimationExample extends StatefulWidget {
  @override
  _AnimationExampleState createState() => _AnimationExampleState();
}

class _AnimationExampleState extends State<AnimationExample> with TickerProviderStateMixin {
  AnimationController controller;

  @override
  void initState() {
    super.initState();
    controller = AnimationController(
      vsync: this, duration: Duration(seconds: 5)
    );
    controller.forward();
  }

  _onTap() {
    if (controller.status == AnimationStatus.completed || controller.status == AnimationStatus.forward) {
      controller.reverse();
    } else {
      controller.forward();
    }
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: GestureDetector(
        onTap: _onTap,
        child: AnimatedBox(
          listenable: controller,
        ),
      ),
    );
  }
}

class AnimatedBox extends AnimatedWidget {
  AnimatedBox({listenable}) : super(listenable: listenable);
  Tween tween = Tween(begin: 100.0, end: 200.0);

  @override
  Widget build(BuildContext context) {
    final Animation<double> animation = listenable;
    return Container(
      color: Colors.green,
      width: tween.evaluate(animation),
      height: tween.evaluate(animation),
    );
  }
}