Flutter count App with InheritedWidget

count_inherited_widget.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter State Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Counter(),
    );
  }
}

class _InheritedCounter extends InheritedWidget {
  _InheritedCounter({Key key, @required this.counterState, @required this.child})
      : assert(counterState != null),
        super(key: key, child: child);

  final _CounterState counterState;
  final Widget child;

  @override
  bool updateShouldNotify(_InheritedCounter old) => counterState.count != old.counterState.count;
}

class Counter extends StatefulWidget {
  Counter({Key key}) : super(key: key);

  @override
  _CounterState createState() => _CounterState();

  static _CounterState of(BuildContext context) {
    return (context.inheritFromWidgetOfExactType(_InheritedCounter)
        as _InheritedCounter).counterState;
  }
}

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

  void increment() {
    setState(() {
      count++;
    });
  }

  void decrement() {
    setState(() {
      count--;
    });
  }

  @override
  Widget build(BuildContext context) {
    return _InheritedCounter(
      child: CounterUI(),
      counterState: this,
    );
  }
}

class CounterUI extends StatelessWidget {
  Widget _fab(Icon icon, Function action) {
    return FloatingActionButton(
      child: icon,
      onPressed: action,
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Count Sample State Management'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '${Counter.of(context).count}',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: Column(
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          _fab(Icon(Icons.exposure_plus_1), Counter.of(context).increment),
          _fab(Icon(Icons.exposure_neg_1), Counter.of(context).decrement),
        ],
      ),
    );
  }
}