我如何从Dart流中的回调函数产生值

Question

I have the following stream defined in my flutter application:

  static Stream<String> downloadIdentifiers() async* {
    try {
      yield "test";
      final directory = await getApplicationDocumentsDirectory();

      Response response;
      Dio dio = new Dio();
      response = await dio.download(
        MyConstants.identifiersUrl,
        join(directory.path, "identifiers.json"),
        onReceiveProgress: (int received, int total) {
          print("$received / $total");
        },
      );
      yield join(directory.path, "identifiers.json");
    } catch (ex) {
      throw ex;
    }
  }

I am using https://github.com/flutterchina/dio for the download.

I want to yield information about the download progress to my stream, but the callback on onReceiveProgress only takes a regular function as callback.

How can I get the information on received / total bytes to yield on my Stream?

Thank you!

Answer 1

Thanks to jamesdlin for the answer. I finally did it like this with his help:

  static Stream<String> downloadIdentifiers() async* {
    StreamController<String> streamController = new StreamController();
    try {
      final directory = await getApplicationDocumentsDirectory();

      Dio dio = new Dio();
      dio.download(
        MyConstants.identifiersUrl,
        join(directory.path, "identifiers.json"),
        onReceiveProgress: (int received, int total) {
          streamController.add("$received / $total");
          print("$received / $total");
        },
      ).then((Response response) {
        streamController.add("Download finished");
      })
      .catchError((ex){
        streamController.add(ex.toString());
      })
      .whenComplete((){
        streamController.close();
      });
      yield* streamController.stream;
    } catch (ex) {
      throw ex;
    }
  }