Widget Caching (Pierre Martin)

child_builder_demo.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class ChildBuilder extends StatelessWidget {
  const ChildBuilder({
    super.key,
    required this.builder,
    this.child,
  });

  final TransitionBuilder builder;
  final Widget? child;

  @override
  Widget build(BuildContext context) => builder(context, child);
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: ChildBuilder(
          builder: (context, child) {
            return SizedBox(
                height: MediaQuery.sizeOf(context).height, child: child);
          },
          child: Center(
            child: Text('Hello, World!'),
          ),
        ),
      ),
    );
  }
}

widget_cache.dart

import 'package:flutter/widgets.dart';

class WidgetCache<T> extends StatefulWidget {
  const WidgetCache({super.key, required this.value, required this.builder});

  final T value;
  final Widget Function(BuildContext context, T value) builder;

  @override
  State<WidgetCache<T>> createState() => _WidgetCacheState<T>();
}

class _WidgetCacheState<T> extends State<WidgetCache<T>> {
  late Widget cache;
  T? previousValue;

  @override
  Widget build(BuildContext _) {
    if (!identical(widget.value, previousValue)) {
      previousValue = widget.value;
      cache = Builder(
        builder: (context) {
          return widget.builder(context, widget.value);
        },
      );
    }

    return cache;
  }
}

widget_cache_demo.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

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

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  int index = 0;
  String text = 'Some text';

  @override
  void initState() {
    super.initState();
    print('init state');
    WidgetsBinding.instance.addPostFrameCallback((_) {
      print('first rebuild starts');
      setState(() {});
      print('first rebuild ends');

      Future.delayed(Duration(seconds: 2), () {
        print('second rebuild');
        setState(() {
          index = 1;
          text = 'Some other text';
        });
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: WidgetCache(
            value: index,
            builder: (context, value) {
              return Text(text);
            },
          ),
        ),
      ),
    );
  }
}

class WidgetCache<T> extends StatefulWidget {
  const WidgetCache({super.key, required this.value, required this.builder});

  final T value;
  final Widget Function(BuildContext context, T value) builder;

  @override
  State<WidgetCache<T>> createState() => WidgetCacheState<T>();
}

class WidgetCacheState<T> extends State<WidgetCache<T>> {
  late Widget cache;
  T? previousValue;

  @override
  Widget build(BuildContext _) {
    if (!identical(widget.value, previousValue)) {
      print('not identical');
      previousValue = widget.value;
      cache = Builder(
        builder: (context) {
          return widget.builder(context, widget.value);
        },
      );
    }

    return cache;
  }
}