Inherited Widget Example - by Simon Lightfoot - Humpday Q&A :: 22nd November 2023 #Flutter #Dart

inherit_me.dart

// MIT License
//
// Copyright (c) 2023 Simon Lightfoot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

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

class CounterModel {
  CounterModel({this.value = 0});

  int value;

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is CounterModel &&
          runtimeType == other.runtimeType &&
          value == other.value;

  @override
  String toString() {
    return '${describeIdentity(this)}{$value}';
  }
}

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

  @override
  Widget build(BuildContext context) {
    return InheritedCounter(
      child: MaterialApp(
        debugShowCheckedModeBanner: false,
        theme: ThemeData.dark(),
        home: const Home(),
      ),
    );
  }
}

class InheritedCounter extends StatefulWidget {
  const InheritedCounter({
    super.key,
    required this.child,
  });

  final Widget child;

  static InheritedCounterState of(BuildContext context) {
    return context
        .dependOnInheritedWidgetOfExactType<_InheritedCounterScope>()!
        .state;
  }

  @override
  State<InheritedCounter> createState() => InheritedCounterState();
}

class InheritedCounterState extends State<InheritedCounter> {
  var counter = CounterModel();

  void add() {
    setState(() {
      counter.value++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return _InheritedCounterScope(
      state: this,
      counter: counter,
      child: widget.child,
    );
  }
}

class _InheritedCounterScope extends InheritedWidget {
  _InheritedCounterScope({
    required this.state,
    required this.counter,
    required super.child,
  }) : value = counter.value;

  final InheritedCounterState state;
  final CounterModel counter;
  late final int value;

  @override
  bool updateShouldNotify(_InheritedCounterScope oldWidget) {
    print('counter value $value');
    print('oldWidget value ${oldWidget.value}');
    return value != oldWidget.value;
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Inherited Counter'),
      ),
      body: const Center(
        child: CounterDisplay(),
      ),
      floatingActionButton: const CounterAddButton(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return FloatingActionButton(
      onPressed: InheritedCounter.of(context).add,
      child: const Icon(Icons.add),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);
    final counter = InheritedCounter.of(context).counter;
    print('build display $counter');
    return Text(
      'Count: ${counter.value}',
      style: theme.textTheme.displaySmall,
    );
  }
}