flutter Bloc 更新后事件同步与异步详解

flutter_bloc: ^7.3.1

class _TestBlocPageState extends State<TestBlocPage> {
  late TestDartBloc _bloc;
  @override
  void initState() {
    super.initState();
    _bloc = TestDartBloc(TestDartState(0));
  }
  @override
  Widget build(BuildContext context) {
    return BlocBuilder<TestDartBloc, TestDartState>(
      bloc: _bloc,
      builder: (context, state) {
        return Column(
          children: [
            //显示当前的数字结果
            Text(state.num.toString()),
            TextButton(
                onPressed: () {
                  //进行自增操作
                  _bloc.add(IncreaseEvent());
                },
                child: Text('add')),
            TextButton(
                onPressed: () {
                  //进行自减操作
                  _bloc.add(ReduceEvent());
                },
                child: Text('reduce')),
          ],
        );
      },
    );
  }
}

part of 'test_dart_bloc.dart';
/// Bloc state
class TestDartState {
  int num = 0;
  TestDartState(this.num);
}

part of 'test_dart_bloc.dart';
/// Bloc event
@immutable
abstract class TestDartEvent {}
//自增事件
class IncreaseEvent extends TestDartEvent{}
//自减事件
class ReduceEvent extends TestDartEvent{}

import 'dart:async';
import 'package:flutter_bloc/flutter_bloc.dart';
part 'test_dart_event.dart';
part 'test_dart_state.dart';
class TestDartBloc extends Bloc<TestDartEvent, TestDartState> {
  TestDartBloc(TestDartState state) : super(state);
  @override
  Stream<TestDartState> mapEventToState(TestDartEvent event) async* {
    if (event is IncreaseEvent) {
      await Future.delayed(Duration(seconds: 10));
      yield TestDartState(state.num + 1);
    } else if (event is ReduceEvent) {
      yield TestDartState(state.num - 1);
    }
  }
}

  /// **@Deprecated - Use on<Event> instead. Will be removed in v8.0.0**
  ///
  /// Must be implemented when a class extends [Bloc].
  /// [mapEventToState] is called whenever an [event] is [add]ed
  /// and is responsible for converting that [event] into a new [state].
  /// [mapEventToState] can `yield` zero, one, or multiple states for an event.
  @Deprecated('Use on<Event> instead. Will be removed in v8.0.0')
  Stream<State> mapEventToState(Event event) async* {}

class TestDartBloc extends Bloc<TestDartEvent, TestDartState> {
  TestDartBloc(TestDartState state) : super(state) {
    init();
  }
  void init() {
    on<IncreaseEvent>((event, emit) async {
      await Future.delayed(Duration(seconds: 10));
      emit(TestDartState(state.num + 1));
    });
    on<ReduceEvent>((event, emit) {
      state.num - 1;
      emit(state);
    });
  }
}

    on<IncreaseEvent>((event, emit) async {
      await Future.delayed(Duration(seconds: 10));
      emit(TestDartState(state.num + 1));
    },
    transformer: (events, mapper) => events.asyncExpand(mapper),
);