Animation Class: Mixin

https://medium.com/flutter-community/dart-what-are-mixins-3a72344011f3

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

class AnimationTest extends StatefulWidget {
  @override  _AnimationTestState createState() => _AnimationTestState();
}

class _AnimationTestState extends State<AnimationTest> with SingleTickerProviderStateMixin{

  AnimationController animationController;

  @override  void initState() {
    // TODO: implement initState    super.initState();
    animationController = new AnimationController(
      vsync: this,
      duration: new Duration(seconds: 5),
    );
    animationController.addListener((){
      this.setState((){});
    });
  }

  @override  Widget build(BuildContext context) {
    return new GestureDetector(
      child: new Container(
        color:Colors.white,
      child: new Center(
        child: new Text(
          animationController.isAnimating?
          animationController.value.toStringAsFixed(3):
          "Press to start!",
          style: TextStyle(color:Colors.black,
            decoration: TextDecoration.underline,
            decorationColor: Colors.black,
          ),
        ),
      ),
      ),
      onTap: (){
        animationController.forward(from: 0.0);
      },
    );
  }

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

}