通过EventChannel接收来自Android的字符串

Question

我目前正在学习Flutter，特别是如何与设备本身进行通信。

目前我已经设置了一个MethodChannel，我在其中接收一个字符串列表作为结果，但是现在我想将它更改为通过一个EventChannel在流上接收这些字符串。

我知道我仍然需要依赖MethodChannel来触发Android端的方法，然后它通过EventChannel将数据(在我的例子中是String)发送回flutter。但是我真的不知道如何让EventChannel只发送几个流(可能在它们之间有一点延迟)，因为我发现的每个关于EventChannel的教程对我来说都是困惑而不是有用的:(

下面是我目前通过EventChannel获取内容的代码：

flutter-plugin：

static const EventChannel messageChannel = EventChannel('eventChannelStream');

  Stream<String> get messageStream async* {
    messageChannel.receiveBroadcastStream().map((message) {
      return message;
    });
  }

android端的Kotlin代码：

class HelperPlugin : FlutterPlugin, MethodCallHandler, EventChannel.StreamHandler {

    private lateinit var channel: MethodChannel
    private var messageChannel: EventChannel? = null
    private var eventSink: EventChannel.EventSink? = null

    override fun onListen(arguments: Any?, eventSink: EventChannel.EventSink?) {
        this.eventSink = eventSink
    }

    override fun onCancel(arguments: Any?) {
        eventSink = null
        messageChannel = null
    }

    override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
        channel = MethodChannel(flutterPluginBinding.binaryMessenger, "methodChannel")
        channel.setMethodCallHandler(this)

        messageChannel = EventChannel(flutterPluginBinding.binaryMessenger, "eventChannelStream")
        messageChannel?.setStreamHandler(this)
    }


... 
// Doing other stuff here

以及我希望如何在BLoC中使用这些消息，以便在事件发生后将它们发送到UI：

Stream<String> retrieveMessage(Stream<String> messageStream) async* {
  await for (String message in messageStream) {
    //await Future.delayed(const Duration(milliseconds: 1500));
    yield message;
  }
}

Answer 1

好了，开始工作了。这可能不是最好的方法，但至少它是有效的:)

下面是我是如何做到的，也许它可以帮助其他人:)：

Android响应的Kotlin代码：

class HelperPlugin : FlutterPlugin, MethodCallHandler, EventChannel.StreamHandler {

    private lateinit var channel: MethodChannel
    private var messageChannel: EventChannel? = null
    private var eventSink: EventChannel.EventSink? = null


    override fun onListen(arguments: Any?, eventSink: EventChannel.EventSink?) {
        this.eventSink = eventSink
    }

    override fun onCancel(arguments: Any?) {
        eventSink = null
        messageChannel = null
    }

    override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
        channel = MethodChannel(flutterPluginBinding.binaryMessenger, "methodChannel")
        channel.setMethodCallHandler(this)

        messageChannel = EventChannel(flutterPluginBinding.binaryMessenger, "eventChannelStream")
        messageChannel?.setStreamHandler(this)
    }

    override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {
        when (call.method) {
            "getPlatformVersion" -> {
                result.success(tellVersionNumber())
            }
            "tellJoke" -> {
                result.success(tellJoke())
            }
            "cantAnswer" -> {
                result.success(cantAnswer())
            }
            "whoAreYou" -> {
                result.success(whoAreYou())
            }
            "currentTime" -> {
                result.success(currentTime())
            }
            "upTime" -> {
                result.success(upTime())
            }
            "greetUser" -> {
                result.success(greetUser())
            }
            "systemInformation" -> {
                result.success(systemInformation())
            }
            else -> {
                result.notImplemented()
            }
        }
    }

    override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {
        channel.setMethodCallHandler(null)
    }

// Here are Functions, which add Strings to the EventChannel via eventSink?.success("String to Add")

}

Flutter-Plugin：

class ChatbotHelper extends ChatbotInterface {
  static const MethodChannel _channel = MethodChannel('methodChannel');
  static const EventChannel messageChannel = EventChannel('eventChannelStream');

  Stream<String> get messageStream async* {
    await for (String message in messageChannel.receiveBroadcastStream().map((message) => message)){
      yield message;
    }
  }

  @override
  Future<void> platformVersion() async {
    await _channel.invokeMethod('getPlatformVersion');
  }

  @override
  Future<void> tellJoke() async {
        await _channel.invokeMethod('tellJoke');
  }
// other invokeMethods and answerQuestion function, which calls these invokeMethods depending on a String message

...

}

下面是我如何在我的BLoC中使用流：

 Future<void> _initializeAnswerStream(
      InitializeMessageStreamEvent event, Emitter<ChatState> emit) async {
    try{
        await for(String message in retrieveMessageStream(_helper.messageStream)) {

        add(AddResponseMessageEvent(responseMessage: message));
      }
    }catch(e){
      print(e);
    }
  }

在我的窗口小部件树中创建相应的BlocProvider时，将调用此BLoC-Event来初始化流并等待消息。

编辑:修复了一些我重命名的值，将其发布在这里