mvvm_plus 0.5.0

MVVM+ is a lightweight Flutter state management library that implements MVVM, plus adds support for sharing business logic across widgets.

example/lib/main.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:mvvm_plus/mvvm_plus.dart';
import 'package:registrar/registrar.dart';

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

Widget myApp() => Registrar<ColorService>(
    builder: () => ColorService(milliSeconds: 1500),
    child: MaterialApp(
        debugShowCheckedModeBanner: false,
        home: Registrar<ColorService>(
          builder: () => ColorService(milliSeconds: 2250),
          location: Location.tree,
          child: Page(),
        )));

class IncrementButton extends View<IncrementButtonViewModel> {
  IncrementButton({super.key})
      : super(builder: () => IncrementButtonViewModel());

  @override
  Widget build(BuildContext context) {
    return FloatingActionButton(
      onPressed: viewModel.incrementCounter,
      child: Text(viewModel.label, style: const TextStyle(fontSize: 24)),
    );
  }
}

class IncrementButtonViewModel extends ViewModel {
  bool isNumber = false;
  String get label => isNumber ? '+1' : '+a';
  void incrementCounter() {
    isNumber
        ? get<PageViewModel>().incrementNumberCounter()
        : get<PageViewModel>().incrementLetterCounter();
    isNumber = !isNumber;
    buildView();
  }
}

class Page extends View<PageViewModel> {
  Page({super.key})
      : super(location: Location.registry, builder: () => PageViewModel());

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
            child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
              Row(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Text(viewModel.letterCount.value,
                        style: TextStyle(
                            fontSize: 64,
                            color: listenTo<ColorService>(context: context)
                                .color)),
                    Text(viewModel.numberCounter.toString(),
                        style: TextStyle(
                            fontSize: 64,
                            color: listenTo<ColorService>().color)),
                  ]),
            ])),
        floatingActionButton: IncrementButton());
  }
}

class PageViewModel extends ViewModel {
  int numberCounter = 0;
  late final letterCount = ValueNotifier<String>('a')..addListener(buildView);

  void incrementNumberCounter() {
    numberCounter = numberCounter == 9 ? 0 : numberCounter + 1;
    buildView();
  }

  void incrementLetterCounter() => letterCount.value = letterCount.value == 'z'
      ? 'a'
      : String.fromCharCode(letterCount.value.codeUnits[0] + 1);
}

class ColorService extends Model {
  ColorService({required int milliSeconds}) {
    _timer = Timer.periodic(Duration(milliseconds: milliSeconds), (_) {
      color = <Color>[
        Colors.red,
        Colors.black,
        Colors.blue,
        Colors.orange
      ][++_counter % 4];
      notifyListeners();
    });
  }

  int _counter = 0;
  Color color = Colors.orange;
  late Timer _timer;

  @override
  void dispose() {
    _timer.cancel();
    super.dispose();
  }
}