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main.dart

import 'package:flutter/material.dart';

void main() {

  runApp(   
    Container(
      color: Colors.lightBlue,
       child: Padding(
         padding: const EdgeInsets.fromLTRB(0.0, 50.0, 0.0, 0.0),
          child: Directionality(
            textDirection: TextDirection.ltr, 
            child: MyStatelessWidget(), 
            //child: MyStatefulWidget(), //uncomment to change widget
            //child: StarWidget(),
        )
     )
    )
  );
}

class MyStatelessWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () => print('you tapped the star'),
      onDoubleTap: () => print('you double tapped the star'),
      onLongPress: () => print('you long pressed the star'),
      child: Icon(Icons.stars, size: 200.0),
    );
  }
}

class StarWidget extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return StarState();
  }
}

class StarState extends State<StarWidget> with SingleTickerProviderStateMixin {
  AnimationController _ac;
  final double _starSize = 300.0;

  @override
  void initState() {
    super.initState();

    _ac = new AnimationController(
      duration: Duration(milliseconds: 750),
      vsync: this,
    );
    _ac.forward();
  }

  @override
  Widget build(BuildContext context) {

    return new AnimatedBuilder(
      animation: _ac,
      builder: (BuildContext context, Widget child) {
        return DecoratedBox(
          child: Icon(Icons.stars, size: _ac.value * _starSize),
          decoration: BoxDecoration(
            gradient: LinearGradient(
              begin: Alignment.topCenter,
              end: Alignment.bottomCenter,
              colors: [Colors.red, Colors.blue, Colors.green],
              tileMode: TileMode.mirror
            ),
          ),
        );
      }
    );
  }
}

class MyStatefulWidget extends StatefulWidget {

  MyStatefulWidget();

  @override
  State<StatefulWidget> createState() {
    return MyWidgetState();
  }
}

class MyWidgetState extends State<MyStatefulWidget> {
  String text = "some text";

  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        FlatButton(
          child: Text('Set State Button'),
          onPressed: () {
            setState(() {
              text = "some new text";
            });
          },
        ),
        Text(
          text, 
          style: TextStyle(fontSize: 20.0)),
      ],
    );
  }
}