Passing data to Flutter based on Android event

Question

Really struggling with the correct way to achieve the following. If I want to make a native call to Android FROM my Flutter app, there are plenty of examples that I can follow. eg: create an EventChannel and then listen for events and respond to requests from within my Android/Kotlin onMessage listener.

However, what I cannot figure out is how to go the other way! I have a native event that is triggering in the background within native Android. When the event occurs, everything works fine and I can print / debug the data, but I cannot figure out the correct way to package this data up and send back up to Flutter to display in the app:

class MainActivity: FlutterActivity() {
....
....
....
fun somethingHappened(firstName: String, lastName: String, eMail: String) {
    Log.d("MyApp","An event has occurred...");
    // Log message is printing out correctly, but need to 
    // create Object / Hashmap / data structure and send to Flutter
}

....
....
}

Can anyone tell me the correct pattern / approach to use and ideally a link to a simple example that I can reference?

Thanks, Jab

api.flutter.dev/javadoc/io/flutter/plugin/common/… - here you can emit "normal" data - success(...) or error -error(...) — pskink
– pskink, Commented Sep 13, 2020 at 16:44
@pskink, thanks for that. I have tried implementing based on examples using EventChannel.EventSink, but I am obviously not doing it correctly as most of the examples that I am seeing are using the EventSink to listen for messages in Android and respond to Flutter. Do you have an example that I could review where the message originates in Android and is dispatched to Flutter? Thanks! — Jablalr
– Jablalr, Commented Sep 13, 2020 at 16:54
no, you listen by implementing onListen - api.flutter.dev/javadoc/io/flutter/plugin/common/… - that method gives you a sink i mentioned above — pskink
– pskink, Commented Sep 13, 2020 at 16:57
something like: EventChannel.StreamHandler handler = new EventChannel.StreamHandler() { @Override public void onListen(Object o, EventChannel.EventSink eventSink) { } @Override public void onCancel(Object o) { } }; FlutterView fv = getFlutterView(); new EventChannel(fv, "my.event.channel").setStreamHandler(handler); — pskink
– pskink, Commented Sep 13, 2020 at 17:03
Thank you @pskink, your comments along with Develocodes helped me to get it working — Jablalr
– Jablalr, Commented Sep 14, 2020 at 8:02

Develocode 777 · Accepted Answer · 2020-09-13 17:05:32Z

4

In MainActivity:

class MainActivity: FlutterActivity() {

    private val CHANNEL = "CHANNEL"

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)

       val channel = MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL);

        channel.invokeMethod("nameOfMethod", "dataToPass")

    }

}

and on flutter side:

MethodChannel channel = MethodChannel('CHANNEL');

  @override
  void initState() {
    
    channel.setMethodCallHandler((call){

      if(call.method == 'nameOfMethod'){
        print(call.arguments);
      }

      return null;
    });
    super.initState();
  }

answered Sep 13, 2020 at 17:05

Develocode 777

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1 Comment

Jablalr Over a year ago

Thank you so much. That helped 1000%. I must have tried 100 different ways and was way over complicating things. Only thing I had to do differently was wrap the Kotlin channel.invokeMethod in a Handler(Looper.getMainLooper()).post {...} or otherwise I was getting an exception in relation to executing on the UI thread. Hope this is the correct way to resolve?

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