Challenge 2 (setState)

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) => MaterialApp(
        home: Scaffold(body: MyWidget()),
      );
}

class MyWidgetState extends State<MyWidget> {
  double scale = 1;

  @override
  Widget build(BuildContext context) => Stack(children: <Widget>[
        Center(
            child: Transform.scale(
          scale: scale,
          child: Container(
            width: 100,
            height: 100,
            color: Colors.yellow,
          ),
        )),
        Positioned(
            bottom: 0,
            left: 0,
            right: 0,
            child: Slider(
              value: scale,
              max: 2,
              onChanged: (newValue) => setState(() => scale = newValue),
            ))
      ]);
}

class MyWidget extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => MyWidgetState();
}