Flutter 的 EventChannel 不向 dart 端发送数据

Question

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我试图在 android 的共享表中显示我的应用程序，我能够成功地做到这一点，但我无法使用EventChannel从本机端向 dart 发送数据。

我已将我的 MainActivity 更新为以下内容

class MainActivity: FlutterActivity() {


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        Log.i("TAG123","onCreate")
        onSharedIntent()
    }

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        Log.i("TAG123","configure flutter engine")


    }

    private fun onSharedIntent() {
        val receivedAction: String? = intent.action
        val receivedType: String? = intent.type
        if (receivedAction == Intent.ACTION_SEND) {

            // check mime type
            if (receivedType?.startsWith("text/") == true) {
                val receivedText: String? = intent.getStringExtra(Intent.EXTRA_TEXT)
                if (receivedText != null) {
                    //do your stuff
                    Log.e("TAG123", receivedText.toString())
                    if(flutterEngine?.dartExecutor?.binaryMessenger != null){
                        Log.i("TAG123","flutter engine not null")
                    }
                    Log.e("TAG123", "here")
                    EventChannel(
                        flutterEngine!!.dartExecutor,
                        "sharePlatform"
                    ).setStreamHandler(object : EventChannel.StreamHandler {

                        override fun onListen(arguments: Any, events: EventSink) {
                            Log.e("TAG123", "here123")
                            events.success(receivedText)
                        }

                        override fun onCancel(arguments: Any) {
                            Log.e("TAG123", "here123456")
                        }
                    })
                } else {
                    Log.e("TAG123", "no data")
                }
            } else if (receivedType?.startsWith("image/") == true) {
//                val receiveUri: Uri? = intent.getParcelableExtra(Intent.EXTRA_STREAM) as Uri?

                val receiveUri = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
                    intent.getParcelableExtra(Intent.EXTRA_STREAM, Uri::class.java)
                } else {
                    intent.getParcelableExtra(Intent.EXTRA_STREAM) as Uri?
                }

                if (receiveUri != null) {
                    Log.e("TAG123", receiveUri.toString())
                    if(flutterEngine?.dartExecutor?.binaryMessenger != null){
                        Log.i("TAG123","flutter engine not null")
                    }
                    EventChannel(
                        flutterEngine!!.dartExecutor,
                        "sharePlatform"
                    ).setStreamHandler(object : EventChannel.StreamHandler {

                        override fun onListen(arguments: Any, events: EventSink) {
                            Log.e("TAG123", "here123")
                            events.success(receiveUri)
                        }

                        override fun onCancel(arguments: Any) {
                            Log.e("TAG123", "here123456")
                        }
                    })
                } else {
                    Log.e("TAG123", "no image data")
                }
            }
        } else if (receivedAction == Intent.ACTION_MAIN) {
            Log.e("TAG123", "onSharedIntent: nothing shared")
        }
    }

}

我也对AndroidManifest进行了必要的更改

<intent-filter>
                <action android:name="android.intent.action.SEND" />

                <category android:name="android.intent.category.DEFAULT" />
                <data android:mimeType="image/*" />
                <data android:mimeType="text/*" />
            </intent-filter>

当我在日志中将它从其他应用程序共享到我的应用程序时，我可以看到 url 或图像的 uri，但EventChannel从不工作

下面是我的 dart 代码

class _MyHomePageState extends State<MyHomePage> {
  var data = "";
  final _eventChannel = const EventChannel('sharePlatform');

  @override
  void initState() {
    super.initState();

    _eventChannel.receiveBroadcastStream().distinct().map((dynamic event) {
      debugPrint("TAG123Flutter $event");
      setState(() {
        data = event;
      });
      // return event;
    });
  }......

Answer 1

这是因为你没有订阅stream，你在stream上操作，只是在MyHomePage初始化的时候。 如果你对这个话题不熟悉，我建议多学习一下事件驱动编程，在 Dart 阅读写可视化它会让人感到困惑。

StreamSubscription<dynamic>? _eventSubscription;

  @override
  void initState() {
    super.initState();

    _eventSubscription = _eventChannel.receiveBroadcastStream().listen((dynamic event) {
      debugPrint("TAG123Flutter $event");
      setState(() {
        data = event;
      });
    });

  }

  @override
  void dispose() {
    _eventSubscription?.cancel(); // Cancel the event subscription when the widget is disposed
    super.dispose();
  }

这样，小部件将监听只要它还活着就发生的事件。

如果你想使用distinct ，你可以使用 StreamTransformer。 例如，

StreamTransformer<String, String> distinctTransformer =
    StreamTransformer<String, String>.fromHandlers(
  handleData: (String data, EventSink<String> sink) {
    Set<String> uniqueItems = Set<String>();
    if (!uniqueItems.contains(data)) {
      uniqueItems.add(data);
      sink.add(data);
    }
  },
);

StreamSubscription<String> _streamSubscription;
_streamSubscription = _streamController.stream
    .transform(distinctTransformer)
    .listen((data) {
      print('Received distinct data: $data');
    });