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

void main() {
  runApp(new MaterialApp(
    home: new MyApp(),
  ));
}

class MyApp extends StatefulWidget {
  @override
  _State createState() => new _State();
}

class _State extends State<MyApp> with TickerProviderStateMixin {

  Animation<double> animation;
  AnimationController controller;
  static final _opacityTween = new Tween<double>(begin: 0.1, end: 1.0);
  static final _sizeTween = new Tween<double>(begin: 0.0, end: 300.0);

  initState() {
    super.initState();
    controller = new AnimationController(duration: const Duration(milliseconds: 2000), vsync: this);
    animation = new CurvedAnimation(parent: controller, curve: Curves.easeIn);
    animation.addStatusListener(listener);
    controller.forward();

  }

  void listener(AnimationStatus status) {
    if(status == AnimationStatus.completed) {
      controller.reverse();
    } else if (status == AnimationStatus.dismissed) {
      controller.forward();
    }
  }



  @override
  Widget build(BuildContext context) {

    print(_opacityTween.evaluate(animation));

    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Name here'),
      ),
      body: new Container(
        padding: new EdgeInsets.all(32.0),
        child: new Center(
          child: new Opacity(
            opacity: _opacityTween.evaluate(animation),
            child: new Container(
              margin: new EdgeInsets.symmetric(vertical: 10.0),
              height: _sizeTween.evaluate(animation),
              width: _sizeTween.evaluate(animation),
              child: new FlutterLogo(),
            ),
          ),
        ),
      ),
    );
  }
}