如何在一个 ReceivePort dart 上进行多个订阅答案

【问题标题】：How to make multiple subscription on one ReceivePort dart如何在一个 ReceivePort dart 上进行多个订阅
【发布时间】：2021-11-20 02:47:28
【问题描述】：

我的任务是创建 N 个隔离区，以及一个将传递给这些隔离区的主 ReceivePort，通过使用此 ReceivePort，我传递了函数所需的所有信息，以提供理想的输出。它是第一次工作，但是，任何给这些隔离区的连续消息，并且接收它们都会引发这样的错误

这是我的代码

  //main receive port
  var controlPort = ReceivePort();

  ...
  class _MainScreenState extends State<MainScreen> {
  final ImagePicker _picker = ImagePicker();

  Future<ui.Image>? image;

  @override
  void initState() {
    for (int i = 0; i < Platform.numberOfProcessors; i++) {
      Future<Isolate> isolate =
          Isolate.spawn(Core.readAndMapFast, controlPort.sendPort);
    }
  }

  @override
  Widget build(BuildContext context) {

  ...
  static void readAndMapFast(SendPort sendPort) async {
    //sending SendPort of a created isolate to the main thread
    ReceivePort receivePort = ReceivePort();
    sendPort.send(receivePort.sendPort);

    receivePort.first.then((message) {
    //listening for a message coming from main thread and populating it with all needed 
    //data
      message as Arguments;
      Arguments arguments = Arguments(message.imgList, message.lutList,
          message.imgHeight, message.imgWidth, message.widthLut, message.order);
    //ecexuting all needed operations and after that sending message to the main thread
    ...
      sendPort.send(output);

    //in the main thread we are listening for messages from RecievePort we created at 
    //the very beginning

   await for (dynamic message in controlPort.asBroadcastStream()) {
      if (message is SendPort) {

   //waiting for a message from isolates and if its type is SendPort i.e isolate sending 
   //its first message we are sending needed arguments to a function

        message.send(args[i]);
      } else {
        message as FinalList;
        counter++;
        postEditList.add(message);
        if (counter == numberOfWorkers) {
          Stopwatch timerr = Stopwatch();
          timerr.start();
          for (int t = 0; t < postEditList.length; t++) {
            FinalList list =
                postEditList.where((element) => element.order == t).first;
            bytesBuilder.add(list.imgSubList);
          }
          break;
        }
      }
    }

我建议我必须使用 ReceivePort().asBroadcastStream()，但是我不能用它发送消息和做其他事情。因为变成stream之后，我们就没有SendPort了。

【问题讨论】：

标签： flutter asynchronous stream dart-isolates

【解决方案1】：

我想出了解决办法。这很容易。我们有一个主要的 ReceivePort，我们将使用它来跨隔离区和主线程进行通信，并且我们还创建了一个 BroadcastStream，它将用于侦听来自我们的 ReceivePort 的任何更新。

var controlPort = ReceivePort();
var broadcastStream = controlPort.asBroadcastStream();

那么你所要做的就是监听broadcastStream的更新而不是controlPort by

broadcastStream.listen((event) {});

希望对遇到同样问题的朋友有所帮助

【讨论】：