layout widget switching problem

main.dart

// Copyright 2019 the Dart project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file.

import 'dart:async';
import 'dart:math';

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        colorSchemeSeed: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}



class MyHomePage extends StatefulWidget {
  final String title;

  const MyHomePage({
    super.key,
    required this.title,
  });

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

enum ExampleState{
  loading,
  error,
  content,
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  final ValueNotifier<ExampleState> notifier = ValueNotifier(ExampleState.loading);
  
  late final Timer _timer;
  
  void initState(){
    super.initState();
    _timer = Timer.periodic(Duration(seconds: 3), (_) {
    final value = notifier.value;
    notifier.value = switch (value) {
      ExampleState.loading => ExampleState.content,  
      ExampleState.content => ExampleState.error,  
      ExampleState.error => ExampleState.loading,  
    };
  });
  }
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: ListenableBuilder(
        listenable: notifier,
          builder: (context, _) => switch (notifier.value) {
            ExampleState.loading => ExampleLayoutWidget.loading(),
            ExampleState.content => ExampleLayoutWidget.content(),
            ExampleState.error => ExampleLayoutWidget.error(failure: Object()),
          },
        )
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

abstract class ExampleLayoutWidget extends StatefulWidget {
  const ExampleLayoutWidget._({
    super.key,
  });

  factory ExampleLayoutWidget.loading({
    Key? key,
  }) =>
      _ExampleLayoutWidgetLoading._(
        key: key,
      );

  factory ExampleLayoutWidget.error({
    required Object failure,
    Key? key,
  }) =>
      _ExampleLayoutWidgetError._(
        failure: failure,
        key: key,
      );

  factory ExampleLayoutWidget.content() => _ExampleLayoutWidgetContent._();
  
}

class _ExampleLayoutWidgetError extends ExampleLayoutWidget {
  const _ExampleLayoutWidgetError._({
    required Object failure,
    super.key,
  }) : super._();


  
  @override
  State<_ExampleLayoutWidgetError> createState() => _ExampleLayoutWidgetErrorState();
}

class _ExampleLayoutWidgetErrorState extends State<_ExampleLayoutWidgetError> {
  @override
  Widget build(BuildContext context) {
    return ColorBoxy(child: Center(
      child: Text('error'),
    ));
  }
}

class _ExampleLayoutWidgetContent extends ExampleLayoutWidget {
  const _ExampleLayoutWidgetContent._({
    super.key,
  }) : super._();


  
  @override
  State<_ExampleLayoutWidgetContent> createState() => _ExampleLayoutWidgetContentState();
}

class _ExampleLayoutWidgetContentState extends State<_ExampleLayoutWidgetContent> {
  @override
  Widget build(BuildContext context) {
    return ColorBoxy(child: const Center(
      child: Text('done'),
    ));
  }
}
class _ExampleLayoutWidgetLoading extends ExampleLayoutWidget {
  const _ExampleLayoutWidgetLoading._({
    super.key,
  }) : super._();


  
  @override
  State<_ExampleLayoutWidgetLoading> createState() => _ExampleLayoutWidgetLoadingState();
}

class _ExampleLayoutWidgetLoadingState extends State<_ExampleLayoutWidgetLoading> {
  @override
  Widget build(BuildContext context) {
    return ColorBoxy(child: const Center(
      child: CircularProgressIndicator(),
    ));
  }
}
class ColorBoxy extends StatefulWidget {
  const ColorBoxy({super.key, required this.child,});
  
  final Widget child;

  @override
  State<ColorBoxy> createState() => _ColorBoxyState();
}

class _ColorBoxyState extends State<ColorBoxy> {

  late final Color color =  Color((Random().nextDouble() * 0xFFFFFF).toInt()).withOpacity(1.0);

  @override
  Widget build(BuildContext context) {
    return ColoredBox(color: color, child: widget.child);
  }
}