How to listen a startActivityForResult call when using FlutterPlugin?

Question

I'm developing a Flutter Plugin for Android using Java. When i call the MethodChannel, I need to call another Android Intent. If I was using an native activity, it would be simple since I can call startActivityForResult and implement the method onActivityResult on the same class.

But, when I develop a Flutter Plugin, I can implement FlutterPlugin, MethodCallHandler and ActivityAware interfaces but how can I start a new activity and listen for async result?

Java code:

public class GetnetPlugin implements FlutterPlugin, MethodCallHandler, ActivityAware {

  private MethodChannel channel;
  private Context context;
  private Activity activity;

  @Override
  public void onAttachedToEngine(@NonNull FlutterPluginBinding flutterPluginBinding) {
    context = flutterPluginBinding.getApplicationContext();
    channel = new MethodChannel(flutterPluginBinding.getBinaryMessenger(), "com.example/method");
    channel.setMethodCallHandler(this);
  }

  @Override
  public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
    channel.setMethodCallHandler(null);
  }

  @Override
  public void onMethodCall(@NonNull MethodCall call, @NonNull Result result) {
    switch (call.method){
      case "makePayment":
        makePayment();
        result.success(true);
        return;
      default:
        result.notImplemented();
        return;
    }
  }

  @Override
  public void onAttachedToActivity(@NonNull ActivityPluginBinding binding) {
    this.activity = binding.getActivity();
  }

  @Override
  public void onDetachedFromActivityForConfigChanges() {
    this.activity = null;
  }

  @Override
  public void onReattachedToActivityForConfigChanges(@NonNull ActivityPluginBinding binding) {
    this.activity = binding.getActivity();
  }

  @Override
  public void onDetachedFromActivity() {
    this.activity = null;
  }

  //This is the method that is called with main action. It starts a new activity by a new intent, then it should listen for a async result
  public void makePayment(){
    Bundle bundle = new Bundle();
    DecimalFormat df = new DecimalFormat("000000000000");
    bundle.putString("amount",  df.format(10));
    bundle.putString("paymentType", "credit");

    Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("getnet://pagamento/v3/payment"));
    intent.putExtras(bundle);

    if(intent != null) {
      intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
      activity.startActivityForResult(intent, REQUEST_CODE);    
    }
  }

  //This is the method that I need to be called after new activity returns a result
  public boolean onActivityResult(int requestCode, int resultCode, Intent data) {
    new Handler(Looper.getMainLooper()).post(new Runnable() {
      @Override
      public void run() {
        channel.invokeMethod("success", data);
      }
    });
  }
}

Flutter side:

class Getnet {
  final MethodChannel _channel =
      const MethodChannel('com.example/method');

  final StreamController _streamController = StreamController.broadcast();

  Getnet() {
    _channel.setMethodCallHandler((call) async {
      final method = call.method;
      switch (method) {
        case 'success':
          _streamController.sink.add({
            "status": 1,
            "msg": call.arguments,
          });
          break;
        case 'error':
          _streamController.sink.add({
            'status': 0,
            'msg': call.arguments['errorMessage'],
          });
          break;
      }
    });
  }

  void dispose() {
    _streamController.close();
  }

  Stream get stream => _streamController.stream;

Future makePayment() async {
    await _channel.invokeMethod('makePayment');
  }
}

Answer 1

I just found the answer on Enrico Ori's post at Medium: https://medium.com/theotherdev-s/mastering-flutter-create-a-plugin-e81242b6065

The solution is to make Plugin implements ActivityAware and PluginRegistry.ActivityResultListener, which demands onActivityResult implementation.