bloc

abstract class CounterEvent {}

class IncrementEvent extends CounterEvent {}

class DecrementEvent extends CounterEvent {}

abstract class CounterState {}

class InitialCounterState extends CounterState {
  final int count = 0;
}

class UpdatedCounterState extends CounterState {
  final int count;

  UpdatedCounterState(this.count);
}

import 'package:bloc/bloc.dart';

class CounterBloc extends Bloc<CounterEvent, CounterState> {
  CounterBloc() : super(InitialCounterState());

  @override
  Stream<CounterState> mapEventToState(CounterEvent event) async* {
    if (event is IncrementEvent) {
      yield UpdatedCounterState(state.count + 1);
    } else if (event is DecrementEvent) {
      yield UpdatedCounterState(state.count - 1);
    }
  }
}

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

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: BlocProvider(
        create: (context) => CounterBloc(),
        child: CounterPage(),
      ),
    );
  }
}

class CounterPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final counterBloc = BlocProvider.of<CounterBloc>(context);

    return Scaffold(
      appBar: AppBar(title: Text('Counter')),
      body: Center(
        child: BlocBuilder<CounterBloc, CounterState>(
          builder: (context, state) {
            if (state is UpdatedCounterState) {
              return Text('Count: ${state.count}');
            }
            return CircularProgressIndicator();
          },
        ),
      ),
      floatingActionButton: Column(
        mainAxisAlignment: MainAxisAlignment.end,
        children: [
          FloatingActionButton(
            onPressed: () => counterBloc.add(IncrementEvent()),
            child: Icon(Icons.add),
          ),
          SizedBox(height: 10),
          FloatingActionButton(
            onPressed: () => counterBloc.add(DecrementEvent()),
            child: Icon(Icons.remove),
          ),
        ],
      ),
    );
  }
}