Flutter widget rebuilds: const vs cached instance vs no caching

main.dart

import 'package:flutter/material.dart';
import 'package:flutter/scheduler.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,
      home: const HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({super.key});

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int _counter = 0;
  bool _useConstChild = false;
  bool _useCachedChild = false;

  late Widget _cachedChild;

  void initState() {
    super.initState();
    _cachedChild = Counter(counter: 0);
  }

  void _incrementCounter() {
    setState(() {
      _counter += 1;
      _cachedChild = Counter(counter: _counter);
    });
  }

  void _rebuild() {
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    final widgetCachingType =
        _useConstChild
            ? 'const'
            : _useCachedChild
            ? 'cached instance'
            : 'none';
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          spacing: 16,
          children: [
            if (_useConstChild)
              const Counter(counter: -1)
            else if (_useCachedChild)
              _cachedChild
            else
              Counter(counter: _counter),
            FilledButton(
              onPressed: _incrementCounter,
              child: Text('Increment'),
            ),
            FilledButton(
              onPressed: _rebuild,
              child: Text('Rebuild the HomePage'),
            ),
            FilledButton(
              onPressed:
                  () => setState(() {
                    _useConstChild = true;
                    _useCachedChild = false;
                  }),
              child: Text('Use const child'),
            ),
            FilledButton(
              onPressed:
                  () => setState(() {
                    _useConstChild = false;
                    _useCachedChild = true;
                  }),
              child: Text('Use cached child'),
            ),
            FilledButton(
              onPressed:
                  () => setState(() {
                    _useConstChild = false;
                    _useCachedChild = false;
                  }),
              child: Text('Don\'t use any widget caching'),
            ),
            Text('Widget caching: ${widgetCachingType}'),
          ],
        ),
      ),
    );
  }
}

class Counter extends StatelessWidget {
  const Counter({super.key, required this.counter});

  final int counter;

  @override
  Widget build(BuildContext context) {
    SchedulerBinding.instance.addPostFrameCallback((_) {
      ScaffoldMessenger.of(context).showSnackBar(
        SnackBar(
          content: Text("Counter rebuilt with value: $counter"),
          duration: Duration(seconds: 1),
        ),
      );
    });
    return Text('$counter', style: Theme.of(context).textTheme.headlineMedium);
  }
}