Inherited Widget Example

inherited_widget_example.dart

import 'package:flutter/material.dart';

void main() {
  runApp(
    InitialCounterValueProvider(
      value: 5,
      child: MaterialApp(
        title: 'Flutter Tutorial',
        home: TutorialHome(),
      ),
    ),
  );
}

class InitialCounterValueProvider extends InheritedWidget {
  const InitialCounterValueProvider({
    Key key,
    @required this.value,
    @required Widget child,
  })  : assert(value != null),
        assert(child != null),
        super(child: child);

  final int value;

  static InitialCounterValueProvider of(BuildContext context) {
    return context
        .dependOnInheritedWidgetOfExactType<InitialCounterValueProvider>();
  }

  @override
  bool updateShouldNotify(InitialCounterValueProvider old) =>
      value != old.value;
}

class TutorialHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(child: Counter()),
    );
  }
}

class Counter extends StatefulWidget {
  // Creates State
  @override
  _CounterState createState() => _CounterState();
}

class _CounterState extends State<Counter> {
  int _counter = 0;

  @override
  initState() {
    super.initState();
  }

  @override
  didChangeDependencies() {
    super.didChangeDependencies();

    final counterValueProvider = InitialCounterValueProvider.of(context);
    _counter = counterValueProvider.value;
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        RaisedButton(
          onPressed: _increment,
          child: Text('Increment'),
        ),
        SizedBox(width: 16.0),
        Text(
          'Count: $_counter',
          style: TextStyle(fontSize: 16.0),
        ),
      ],
    );
  }

  void _increment() {
    setState(() {
      _counter++;
    });
  }
}