dependencies:
  flutter_bloc: ^8.1.3

flutter pub get

import 'package:flutter_bloc/flutter_bloc.dart';

class CounterCubit extends Cubit<int> {
  CounterCubit() : super(0);

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

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

void main() {
  runApp(BlocProvider(
    create: (_) => CounterCubit(),
    child: MyApp(),
  ));
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: CounterPage());
  }
}

class CounterPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Cubit Counter")),
      body: Center(
        child: BlocBuilder<CounterCubit, int>(
          builder: (context, count) => Text('จำนวน: \$count', style: TextStyle(fontSize: 30)),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => context.read<CounterCubit>().increment(),
        child: Icon(Icons.add),
      ),
    );
  }
}