Flutter state management. RxDart + BehaviorSubject + Singleton

counter.dart

import 'package:rxdart/rxdart.dart';

class Counter {
  Counter._();
  static final _instance = Counter._();
  factory Counter() {
    return _instance;
  }

  BehaviorSubject _counter =
      BehaviorSubject.seeded(MyModel(a: 10, b: 'START'));
  get stream => _counter.stream;
  MyModel get current => _counter.value;

  increment() {
    int c = current.a;
    _counter.add(MyModel(a: c + 1, b: 'running'));
  }

  // Observable

}

class MyModel {
  MyModel({this.a, this.b});

  int a;
  String b;
}

home_page.dart

import 'package:behaviour_subject/app/counter.dart';
import 'package:flutter/material.dart';

class HomePage extends StatelessWidget {
  final String title;
  const HomePage({Key key, this.title = "Home"}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: StreamBuilder(
          stream: Counter().stream,
          builder: (context, snapshot) {
            return Column(
              children: <Widget>[
                Text("A ${snapshot.data.a.toString()} + ${snapshot.data.b}"),
                RaisedButton(
                  onPressed: () {
                    Counter().increment();
                  },
                )
              ],
            );
          }),
    );
  }
}

pubspec.yaml

name: behaviour_subject
description: A new Flutter project. Created by Slidy

# The following line prevents the package from being accidentally published to
# pub.dev using `pub publish`. This is preferred for private packages.
publish_to: 'none' # Remove this line if you wish to publish to pub.dev

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1

environment:
  sdk: ">=2.7.0 <3.0.0"

dependencies:
  rxdart: ^0.24.1
  flutter:
    sdk: flutter
  # observable: ^0.22.2


  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.

dev_dependencies:
  flutter_test:
    sdk: flutter

# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec

# The following section is specific to Flutter.
flutter:

  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true

  # To add assets to your application, add an assets section, like this:
  # assets:
  #   - images/a_dot_burr.jpeg
  #   - images/a_dot_ham.jpeg

  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.dev/assets-and-images/#resolution-aware.

  # For details regarding adding assets from package dependencies, see
  # https://flutter.dev/assets-and-images/#from-packages

  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #
  # For details regarding fonts from package dependencies,
  # see https://flutter.dev/custom-fonts/#from-packages