如何从 dart 流中的回调函数生成值

Question

我在我的 flutter 应用程序中定义了以下流：

  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;
    }
  }

我使用https://github.com/flutterchina/dio进行下载。

我想生成有关流的下载进度的信息，但回调onReceiveProgress仅采用常规函数作为回调。

如何获取我的流上已接收/总字节数的信息？

谢谢你！

Answer 1

感谢詹姆斯德林的回答。在他的帮助下我终于做到了：

  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;
    }
  }