androidkotlinflutterdartflutter-platform-channel

Calling a function and passing arguments from Kotlin to Flutter


I am dealing with PlatformChannels trying to communicate from Kotlin to Flutter. Trying actually to do what it is explained on the docs from flutter platform channels, but on the opposite direction:

flutter platfor channels docs

The idea is to call a Flutter function from the configureFlutterEngine function on the MainActivity.kt class.

For that, i do, on Flutter side, main.dart (default example from Flutter):

   class _MyHomePageState extends State<MyHomePage> {

  static const platformChannel = const MethodChannel('myTestChannel');


  @override
  Widget build(BuildContext context) {

    platformChannel.setMethodCallHandler((call){
      print("Hello from ${call.method}");
      return null;
    });


    //
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          //
          //
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
          ],
        ),
      ),
    );
  }
}

And from the Kotlin side, i just try to call the flutter callback method on MainActivity.kt:

override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine)

        val channel = MethodChannel(flutterEngine.dartExecutor.binaryMessenger, "myTestChannel")

        channel.invokeMethod("myTestChannel","the argument from Android")
}

But nothing is printed on the Flutter side when I run the code. No crashes or exception either.


Solution

  • You should be implement below way

    Dart Code

    method_channel_helper.dart

    class AmazonFileUpload {
      static const platform = const MethodChannel('amazon');
      static StreamController<String> _controller = StreamController.broadcast();
    
      static Stream get streamData => _controller.stream;
    
      Future<BaseResponse> uploadFile() async {
        try {
          platform.setMethodCallHandler((call) {
            switch (call.method) {
              case "callBack":
                _controller.add("");
                break;
            }
          });
          final Map result = await platform.invokeMethod('s3_upload');
          return BaseResponse(result["success"], result["error"], "");
        } on PlatformException catch (e) {
          return BaseResponse(false, e.message, "");
        }
      }
    }
    

    home_page.dart

    class _HomePageState extends State<HomePage> {
    
      @override
      void initState() {
        super.initState();
        AmazonFileUpload.streamData.listen((event) {
          print("========$callbackFromKotlinToDart--------");
        });
        AmazonFileUpload().uploadFile();
    
    
    
      @override
      Widget build(BuildContext context) {
    
    }
    

    Android Code

    class MainActivity : FlutterActivity(), TransferListener {
        private val CHANNEL = "amazon"
    
        var methodResult: MethodChannel.Result? = null
        override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
            GeneratedPluginRegistrant.registerWith(flutterEngine);
            val channel = MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL)
    
            channel.setMethodCallHandler { call, result ->
                methodResult = result
                if (call.method == "s3_upload") {
                    //Add you login here 
                    channel.invokeMethod("callBack", "data1")
    
    
    
                }
            }
    
        }