收到新事件时，Flutter Bloc 取消正在运行的事件

Question

我有以下 Bloc

class DeviceBloc extends Bloc<DeviceEvent, DeviceState> {
  DataRepository repository;

  DeviceBloc({@required this.repository}) : super(DeviceInitialState()) {
    on<FetchDevicesEvent>(onFetchResources);
  }

  Future<void> onFetchResources(
      FetchDevicesEvent event, Emitter<DeviceState> emit) async {
    emit.call(DeviceLoadingState());

    try {
      List<DeviceResource> devices = await repository.getResources(event.type);
      emit.call(DeviceLoadedState(devices: devices));
    } catch (e) {
      emit.call(DeviceErrorState(message: e.toString()));
    }
  }
}

当 FetchDevicesEvent 事件被触发时，它会启动一个长时间运行的任务，如果在运行的任务完成之前收到额外的 FetchDevicesEvent 事件，错误的结果将返回给调用者。如何暂停等待的任务并始终在收到新的 FetchDevicesEvent 后立即开始新任务？

Answer 1

自己通过使用 transformer: restartable() 从 bloc_concurrency 包中找到了解决方案

class DeviceBloc extends Bloc<DeviceEvent, DeviceState> {
  DataRepository repository;

  DeviceBloc({@required this.repository}) : super(DeviceInitialState()) {
    on<FetchDevicesEvent>(
      onFetchResources,
      transformer: restartable(),
    );
  }

  Future<void> onFetchResources(
      FetchDevicesEvent event, Emitter<DeviceState> emit) async {
    emit.call(DeviceLoadingState());

    try {
      final List<DeviceResource> devices =
          await repository.getResources(event.type);
      emit.call(DeviceLoadedState(devices: devices));
    } catch (e) {
      emit.call(DeviceErrorState(message: e.toString()));
    }
  }