Counter app with a demo cubit implementation

main.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

// A counter app with a demo cubit implementation. The real cubit works 
// slightly different, but this shows the gist.

// library.dart

class Cubit<T> {
  Cubit(this.state) {
    _controller.add(state);
  }

  T state;
  final _controller = StreamController<T>(); // Need dispose this
  Stream<T> stream() => _controller.stream;

  void emit(T newState) {
    state = newState;
    _controller.add(state);
  }
}

class CubitBuilder<T, C extends Cubit<T>> extends StatelessWidget {
  const CubitBuilder({Key? key, required this.builder}) : super(key: key);

  final AsyncWidgetBuilder<T> builder;

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<T>(
      stream: context.read<C>().stream(),
      builder: builder,
    );
  }
}

// counter.dart

class CounterCubit extends Cubit<int> {
  CounterCubit(int initValue) : super(initValue);

  void increment() => emit(state + 1);
  void decrement() => emit(state - 1);
}

// main.dart

void main() {
  runApp(Provider<CounterCubit>(
      create: (context) => CounterCubit(0), child: const MyApp()));
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('Counter example')),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              CubitBuilder<int, CounterCubit>(
                  builder: (context, snapshot) => Text('${snapshot.data}')),
              Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  TextButton(
                      onPressed: () => context.read<CounterCubit>().increment(),
                      child: const Text('+1')),
                  TextButton(
                      onPressed: () => context.read<CounterCubit>().decrement(),
                      child: const Text('-1')),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }
}