InheritedWidget 샘플

inherited_widget_sample.dart

import 'package:flutter/material.dart';

void main() {
  runApp(
    ChangeNotifierProvider<MyViewModel>(
      value: MyViewModel(),
      child: const MyApp(),
    ),
  );
}

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

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyViewModelTest(),
    );
  }
}

class ChangeNotifierProvider<T extends ChangeNotifier> extends InheritedWidget {
  final T value;

  const ChangeNotifierProvider({
    super.key,
    required super.child,
    required this.value,
  });

  static ChangeNotifierProvider<T> of<T extends ChangeNotifier>(
      BuildContext context) {
    return context
        .dependOnInheritedWidgetOfExactType<ChangeNotifierProvider<T>>()!;
  }

  @override
  bool updateShouldNotify(ChangeNotifierProvider oldWidget) {
    return value != oldWidget.value;
  }
}

class MyViewModel with ChangeNotifier {
  int _count = 0;

  int get count => _count;

  void increment() {
    _count++;
    notifyListeners();
  }
}

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

  @override
  State<MyViewModelTest> createState() => _MyViewModelTestState();
}

class _MyViewModelTestState extends State<MyViewModelTest> {
  @override
  Widget build(BuildContext context) {
    final viewModel = ChangeNotifierProvider.of<MyViewModel>(context).value;

    return Scaffold(
      appBar: AppBar(
        title: Text(viewModel.count.toString()),
      ),
      body: Center(
        child: Column(
          children: [
            ElevatedButton(
              onPressed: () {
                setState(() {
                  viewModel.increment();
                });
              },
              child: const Text('+'),
            ),
            ElevatedButton(
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => const NextScreen()),
                );
              },
              child: const Text('Next'),
            ),
          ],
        ),
      ),
    );
  }
}

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

  @override
  State<NextScreen> createState() => _NextScreenState();
}

class _NextScreenState extends State<NextScreen> {
  @override
  Widget build(BuildContext context) {
    final viewModel = ChangeNotifierProvider.of<MyViewModel>(context).value;

    return Scaffold(
      appBar: AppBar(
        title: Text(viewModel.count.toString()),
      ),
      body: Center(
        child: Column(
          children: [
            ElevatedButton(
              onPressed: () {
                setState(() {
                  viewModel.increment();
                });
              },
              child: const Text('+'),
            ),
            ElevatedButton(
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => const NextScreen()),
                );
              },
              child: const Text('Next'),
            ),
          ],
        ),
      ),
    );
  }
}