Inherited notification listener

main.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

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

class InheritedNotificationListener<T> extends InheritedWidget {
  InheritedNotificationListener({Key key, this.listener, Widget child})
      : super(key: key, child: child);

  static void dispatch<T>(BuildContext context, T value) {
    Type typeof<T>() => T;

    final type = typeof<InheritedNotificationListener<T>>();

    final element = context.ancestorInheritedElementForWidgetOfExactType(type);
    final widget = element?.widget as InheritedNotificationListener<T>;

    widget?.listener(value);
  }

  final void Function(T value) listener;

  @override
  bool updateShouldNotify(InheritedWidget w) => false;
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return InheritedNotificationListener(
      listener: (int value) {
        print('received $value');
      },
      child: MaterialApp(
        title: 'Flutter Demo',
        debugShowCheckedModeBanner: false,
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: MyHomePage(title: 'Flutter Demo Home Page'),
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            InheritedNotificationListener.dispatch(context, 42);
          },
          child: Text('dispatch'),
        ),
      ),
    );
  }
}