theme_inherited_widget.dart

import 'dart:async';

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> {
  ThemeMode themeMode = ThemeMode.light;
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyThemeWidget(
        onChangeTheme: changeTheme,
        themeMode: themeMode,
        child: RootWidget(),
      ),
      darkTheme: ThemeData.dark().copyWith(
        brightness: Brightness.dark,
      ),
      themeMode: ThemeMode.system,
    );
  }

  void changeTheme(ThemeMode themeMode) {
    setState(() {
      this.themeMode = themeMode;
    });
  }
}

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

  @override
  State<RootWidget> createState() => _RootWidgetState();
}

class _RootWidgetState extends State<RootWidget> {
  int _count = 0;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
          child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          ElevatedButton(
            onPressed: () {
              setState(() {
                _count++;
              });
            },
            child: Text('update widget'),
          ),
          Home(
            count: _count,
          ),
        ],
      )),
    );
  }
}

class Home extends StatefulWidget {
  Home({super.key, required this.count});
  final int count;
  @override
  State<Home> createState() => _HomeState();
}

class _HomeState extends State<Home> {
  int _count = 0;
  late Timer _timer;
  @override
  void initState() {
    _timer = Timer.periodic(Duration(seconds: 1), (timer) {
      if (mounted) {
        setState(() {
          _count++;
        });
      }
    });
    super.initState();
  }

  @override
  void didChangeDependencies() {
    print('flutter lifecycle is called didchange dependency');
    super.didChangeDependencies();
  }

  @override
  void didUpdateWidget(covariant Home oldWidget) {
    super.didUpdateWidget(oldWidget);
    print('old count is ${oldWidget.count} new count ${widget.count}');
  }

  @override
  Widget build(BuildContext context) {
    final MediaQueryData mediaQuery = MediaQuery.of(context);
    final String systemTheme = mediaQuery.platformBrightness == Brightness.dark
        ? "Dark Theme"
        : "Light Theme";
    final MyThemeWidget myThemeWidget = MyThemeWidget.of(context);
    final String theme = myThemeWidget.themeMode == ThemeMode.dark
        ? "Dark Theme"
        : "Light Theme";
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Text("device theme is $systemTheme"),
          Divider(),
          Text(
              "widgth is ${mediaQuery.size.width.toInt()} height is ${mediaQuery.size.height.toInt()}"),
          Divider(),
          Text("Current theme is $theme"),
          Text(
            _count.toString(),
            style: TextStyle(fontSize: 34),
          ),
          FloatingActionButton(
            onPressed: () {
              setState(() {
                _count++;
              });
            },
            child: Icon(Icons.add),
          ),
          SwitchListTile(
            title: Text("Dark Theme"),
            value: myThemeWidget.themeMode == ThemeMode.dark,
            onChanged: (isDark) {
              ThemeMode themeMode = isDark ? ThemeMode.dark : ThemeMode.light;
              myThemeWidget.onChangeTheme(themeMode);
            },
          ),
        ],
      ),
    );
  }

  @override
  void deactivate() {
    super.deactivate();
  }

  @override
  void dispose() {
    print('flutter lifecycle is called destoryed ');
    super.dispose();
    if (_timer.isActive) {
      _timer.cancel();
    }
  }
}

class MyThemeWidget extends InheritedWidget {
  const MyThemeWidget({
    required super.child,
    required this.themeMode,
    required this.onChangeTheme,
  });

  final ThemeMode themeMode;
  final Function(ThemeMode) onChangeTheme;
  static MyThemeWidget of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<MyThemeWidget>()!;
  }

  @override
  bool updateShouldNotify(covariant MyThemeWidget oldWidget) {
    return oldWidget.themeMode != themeMode;
  }
}