Flutter native plugin: Example with eventlisteners

Question

I'm looking for an easy to follow example of eventlisteners with native plugins. So for example: The plugin that I'm writing has a lot of listeners that do something when an action failed or is completed. Those listeners can be written in native code, but how would I allow the end user, who writes dart code, to write their own custom listeners? So for example add another variable assignment in an onSuccess event?

I'm searching for a small example for Android and iOS.

---- EDIT ----
I'm working with this code atm:

public static void registerWith(Registrar registrar) {
    final MethodChannel methodChannelGeoFire = new MethodChannel(registrar.messenger(), "com.bram.vanbilsen.geofire.GeoFire");
    final MethodChannel methodChannelGeoQuery = new MethodChannel(registrar.messenger(), "com.bram.vanbilsen.geofire.GeoQuery");
    final EventChannel geoQueryKeyEnteredEventChannel = new EventChannel(registrar.messenger(), "com.bram.vanbilsen.geofire.keyEnteredChannel");
    final EventChannel geoQueryKeyExitedEventChannel = new EventChannel(registrar.messenger(), "com.bram.vanbilsen.geofire.keyExitedChannel");
    final EventChannel geoQueryKeyMovedEventChannel = new EventChannel(registrar.messenger(), "com.bram.vanbilsen.geofire.keyMovedChannel");
    final EventChannel geoQueryQueryReadyEventChannel = new EventChannel(registrar.messenger(), "com.bram.vanbilsen.geofire.queryReadyChannel");
    final EventChannel geoQueryQueryErrorEventChannel = new EventChannel(registrar.messenger(), "com.bram.vanbilsen.geofire.queryErrorChannel");
    final GeofirePlugin instance = new GeofirePlugin(registrar.activity());
    geoQueryKeyEnteredEventChannel.setStreamHandler(instance);
    geoQueryKeyExitedEventChannel.setStreamHandler(instance);
    geoQueryKeyMovedEventChannel.setStreamHandler(instance);
    geoQueryQueryReadyEventChannel.setStreamHandler(instance);
    geoQueryQueryErrorEventChannel.setStreamHandler(instance);
    methodChannelGeoFire.setMethodCallHandler(instance);
    methodChannelGeoQuery.setMethodCallHandler(instance);
}

GeofirePlugin(Activity activity) {
  this.activity = activity;
}

private final Activity activity;

And

if (call.method.equals("addGeoQueryEventListener")) {
  String refPath = call.argument("refPath");
  DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
  GeoFire geofire = new GeoFire(ref);
  List center = call.argument("center");
  double radius = call.argument("radius");
  GeoQuery query = geofire.queryAtLocation(new GeoLocation(center.get(0), center.get(1)), radius);
  query.addGeoQueryEventListener(new GeoQueryEventListener() {
    @Override
    public void onKeyEntered(String key, GeoLocation location) {
      System.out.println("entered");
    }

    @Override
    public void onKeyExited(String key) {
      System.out.println("exited");
    }

    @Override
    public void onKeyMoved(String key, GeoLocation location) {
      System.out.println("moved");
    }

    @Override
    public void onGeoQueryReady() {

    }

    @Override
    public void onGeoQueryError(DatabaseError error) {
      System.out.println(error.getMessage());
    }
  });
}

My onListen and onCancel methods are still empty. I'd like to setupgeoQueryQueryReadyEventChannel first . I'd like to send over data with this channel whenever onGeoQueryReady in the GeoQueryEventListener picks something up. How can I achieve this? My main problem is that I don't understand how I can link the GeoQueryEventListener in an onListen method to a local GeoQuery instance.

user_6385579 · Answer

Hope this will help...

EventChannel eventChannelService = new 
        EventChannel(registrar.messenger(), "com.xyz");
eventChannelService.setStreamHandler(
        new GeofirePlugin(registrar.activity()));

The GeoFirePlugin look like :

public class GeofirePlugin implements EventChannel.StreamHandler {

    @Override
    public void onListen(Object o, final EventChannel.EventSink eventSink) {
        Log.e("Success", "cancelling listener");
    }

    @Override
    public void onCancel(Object o) {
        Log.e("Error", "cancelling listener");
    }
}

Flutter native plugin: Example with eventlisteners

2 Answers