An inherited callback pattern to change InheritedWidget state in flutter

main.dart

import 'package:flutter/material.dart';
import 'package:flutter_login_manager/splash_screen.dart';
import 'package:flutter_login_manager/model/login_info.dart';
import 'package:flutter_login_manager/model/login.dart' as loginManager;
import 'package:flutter_login_manager/home_screen.dart';

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

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => MyAppState();
}

class MyAppState extends State<MyApp> {
  int number;

  void numChangeCallback(int receivedNum) {
    setState(() {
      number = receivedNum;
    });
  }

  @override
  void initState() {
    super.initState();
    number = 0;
  }

  @override
  Widget build(BuildContext context) =>
      MaterialApp(
        theme: ThemeData(
          primarySwatch: Colors.red,
        ),
        home: NumManager(
            number: number,
            callback: numChangeCallback,
            child: Builder(builder: homeScreenBuilder)
        ),
      );
}

Widget homeScreenBuilder(BuildContext context) {
  int _number = NumManager
      .of(context)
      .number;
  Function(int) _callback = NumManager
      .of(context)
      .callback;
  return Scaffold(
    appBar: AppBar(
      title: Text('Inherited Callback Pattern'),
      elevation: 0.0,
    ),
    floatingActionButton: FloatingActionButton(onPressed: () {
      _callback(++_number);
    },child: Text('+1'),),
    body: Center(
      child: Text(_number.toString(),style: TextStyle(fontSize: 40.0, color: Colors.red, fontWeight: FontWeight.w900),),
    ),
  );
}

class NumManager extends InheritedWidget {
  final int number;
  final Widget child;
  final Function(int) callback;
  final Key key;

  NumManager({@required this.number,
    @required this.callback,
    @required this.child,
    this.key})
      : super(key: key);

  @override
  bool updateShouldNotify(NumManager oldWidget) {
    return oldWidget.number == number;
  }

  static NumManager of(BuildContext context) =>
      context.inheritFromWidgetOfExactType(NumManager);
}

InheritedCallbackPattern

Inherited Callback Allows you to change the values of the state distributed downwards by the InheritedWidget

The Problem

The problem with InheritedWidgets is that all the fields inside it are final. As a result, we can only get, and not set the values inside it. This makes it ideal for holding state, but we do require some way to change state from below the tree.

The Solution

Inherit a callback. The Stateful Widget coupled with the InheritedWidget can expose a callback via the InheritedWidget.

The Result

It Works!

This! is a simple Inheritedwidget Example! Thanks