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



class CounterState {
  int counter;
  static final CounterState _state=CounterState._();
  CounterState._(){
    counter=0;
  }

  factory CounterState() {
    return _state;
  }
}

abstract class CounterEvent {}

class IncrementEvent extends CounterEvent {}

class DecrementEvent extends CounterEvent {}

class CounterBloc extends Bloc<CounterEvent, CounterState> {
  @override
  CounterState get initialState => CounterState();

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


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

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

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

    return Scaffold(
      appBar: AppBar(title: Text('Counter')),
      body: Center(
        child: BlocBuilder<CounterBloc, CounterState>(
          builder: (context, count) {
            return Text(
              '${count.counter}',
              style: TextStyle(fontSize: 24.0),
            );
          },
        ),
      ),
      floatingActionButton: Column(
        crossAxisAlignment: CrossAxisAlignment.end,
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          Padding(
            padding: EdgeInsets.symmetric(vertical: 5.0),
            child: FloatingActionButton(
              child: Icon(Icons.add),
              onPressed: () {
                counterBloc.add(IncrementEvent());
              },
            ),
          ),
          Padding(
            padding: EdgeInsets.symmetric(vertical: 5.0),
            child: FloatingActionButton(
              child: Icon(Icons.remove),
              onPressed: () {
                counterBloc.add(DecrementEvent());
              },
            ),
          ),
        ],
      ),
    );
  }
}