NumbersApp which swaps two int values is for visualizing "Keys under the hood".

README.md

NumbersApp which swaps two int values is for visualizing "Keys under the hood" -- Blog post on medium

main.dart

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

class NumbersApp extends StatefulWidget {
  @override
  _NumbersAppState createState() => _NumbersAppState();
}

class _NumbersAppState extends State<NumbersApp> {

  
  late List<Widget> children;

  @override
  void initState() {
    children = [
     StatelessNumber(),
     StatelessNumber(),
    ];
    super.initState();
  }
  
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Column(
              children: children,
            ),
            
            ElevatedButton(
                onPressed: () {
                  setState(() {
                    children.insert(1, children.removeAt(0));
                  });
                },
                child: Text("Swap")
            )
            
          ],
        ),
      ),
    );
  }
}

class StatelessNumber extends StatelessWidget {
  int count = NumberGenerator.getNumber();

  @override
  Widget build(BuildContext context) {
    return Text('Count: $count', style: TextStyle(fontSize: 20),);
  }
}

class StatefulNumber extends StatefulWidget {

  const StatefulNumber({Key? key}) : super(key: key);


  @override
  _StatefulNumberState createState() => _StatefulNumberState();
}

class _StatefulNumberState extends State<StatefulNumber> {
  late int count;

  @override
  void initState() {
    super.initState();
    count = NumberGenerator.getNumber();
  }

  @override
  Widget build(BuildContext context) {
    return Text('Count: $count', style: TextStyle(fontSize: 20),);
  }
}

class NumberGenerator {
  static List<int> numberOptions = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
  static Random random = new Random();

  static int getNumber() {
    if (numberOptions.length > 0) {
      int number = numberOptions.removeAt(random.nextInt(numberOptions.length));
      return number;
    } else {
      int number = random.nextInt(9); // Generates either 0 or 1
      return number;
    }
  }
}

void main() {
  runApp(MaterialApp(
    theme: ThemeData(
      brightness: Brightness.light,
    ),
    home: NumbersApp(),
  ));
}