我正在使用flutter bloc来显示下载进度百分比，但我一直遇到这个问题。我认为这个问题出现在onDone方法中，但我不知道如何解决它。

错误：

• 发生异常。_AssertionError（'package：bloc/src/bloc. dart'：Assert失败：第137行位置7：'！_isCompleted'：emit在事件处理程序正常完成后被调用。这通常是由于事件处理程序中的未等待的将来。请确保等待事件处理程序的所有异步操作，并在异步操作后调用emit（）之前使用emit.isDone以确保事件处理程序尚未完成。*
  坏

on<Event>((event, emit) {
    future.whenComplete(() => emit(...));
  });

好

on<Event>((event, emit) async {
    await future.whenComplete(() => emit(...));
  });
)

代码：

import 'package:bloc/bloc.dart';
import 'package:download_progress_with_bloc/downlaod_file.dart';
import 'package:download_progress_with_bloc/download_event.dart';
import 'package:download_progress_with_bloc/download_state.dart';
import 'package:download_progress_with_bloc/permission_handler.dart';
import 'package:download_progress_with_bloc/store_book_repo.dart';
import 'package:http/http.dart' as http;

class DownloadBloc extends Bloc<DownloadEvent, DownloadState> {
  DownloadBloc({required this.storeBookRepo}) : super(DownloadInitial()) {
    on<DownloadStarted>(onStarted);
    on<DownloadProgressed>(onProgressed);
  }
  final StoreBookRepo storeBookRepo;

  http.StreamedResponse? response;
  // StreamController? _controller;
  int received = 0;
  List<int> bytes = [];
  int totalSize = 0;

  @override
  Future<void> close() {
    return super.close();
  }

  Future<void> onStarted(
      DownloadStarted event, Emitter<DownloadState> emit) async {
    try {
      await PermissionHandler.requestStoragePermission();
      response = await downloadFile();
      totalSize = response!.contentLength ?? 0;
      emit(DownloadInProgress(progress: received, totalSize: totalSize));
      response?.stream.asBroadcastStream().listen((value) async {
        received += value.length;
        bytes.addAll(value);
        add(DownloadProgressed(progress: received));
        print('received value is $received');
      }).onDone(
        () async {
          await storeBookRepo
              .storePdf(
                bytes.toString(),
                bookTitle: 'bookTitle',
              )
              .then((value) => emit(DownloadCompleted()));
          // emit(DownloadCompleted());
        },
      );
    } catch (e) {
      emit(DownlaodFailed(errorMessage: '$e'));
    }
  }

  void onProgressed(DownloadProgressed event, Emitter<DownloadState> emit) {
    emit(DownloadInProgress(progress: event.progress, totalSize: totalSize));
  }

}