如何在flutter中使用BLoC模式添加回调？

dependencies:
  flutter_bloc: ^7.0.0

import 'dart:async';
import 'package:flutter_bloc/flutter_bloc.dart';

class MyBloc extends Bloc<MyEvent, MyState> {
  MyBloc() : super(MyInitialState());

  @override
  Stream<MyState> mapEventToState(MyEvent event) async* {
    if (event is MyEventWithCallback) {
      // 在这里执行回调操作
      event.callback();
      yield MyStateWithCallback();
    }
  }
}

// 定义事件
abstract class MyEvent {}

class MyEventWithCallback extends MyEvent {
  final VoidCallback callback;

  MyEventWithCallback(this.callback);
}

// 定义状态
abstract class MyState {}

class MyInitialState extends MyState {}

class MyStateWithCallback extends MyState {}

BlocBuilder<MyBloc, MyState>(
  builder: (context, state) {
    if (state is MyInitialState) {
      return Text('初始状态');
    } else if (state is MyStateWithCallback) {
      return Text('回调完成');
    }
    return Container();
  },
)

BlocProvider.of<MyBloc>(context).add(MyEventWithCallback(() {
  // 在这里执行回调操作
}));