how do I pass data from native app to flutter?

Question

I have read this https://github.com/flutter/flutter/wiki/Add-Flutter-to-existing-apps.

My problem is to pass data from existing native android app to flutter module (such as: token, username...etc). So, I want to ask if there is any way to pass data between Native code in existing native app and code in flutter module?

For example, there are two pages, A and B, A is written in Java code, B embed flutter view, I didn't find any way to pass data from A to the flutter view in B.

public class TwoActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.two_activity);
        
        //this params passed from HomeActivity 
        String params = getIntent().getStringExtra("params");

        FrameLayout rootView = findViewById(R.id.container);

        View flutterView = Flutter.createView(this, getLifecycle(), "service");

        FrameLayout.LayoutParams layoutParams = new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
        rootView.addView(flutterView, layoutParams);
    }
}

this is main.dart

void main() => runApp(chooseWidget(window.defaultRouteName));

Widget chooseWidget(String route) {
  switch(route) {
    case 'service':
      return MyFlutterView();
  }
}

class MyFlutterView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {

  static const platform = const MethodChannel('samples.flutter.dev/start');

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.white,
      child: Column(
        children: <Widget>[

          Text(
            'this is a flutter page',
            style: TextStyle(
              fontSize: 14,
              color: Colors.blue
            ),
          ),

          FlatButton(
            onPressed: () {
              platform.invokeMethod('startActivity');
            },
            child: Text('go native page'),
            color: Colors.purple,
            highlightColor: Colors.deepPurple,
          )
        ],
      ),
    );
  }
}

-------------------------->edit in 2019.7.18<-----------------------------

Thank you for your help. I found the answer.
1、BasicMessageChannel：use this to pass string or other object.

2、MethodChannel：use this to method invocation

3、EventChannel: use this to event streams

Answer 1

You can use method channel for this

private static final String CHANNEL = "AndySample/test";

FlutterEngine flutterEngine=new FlutterEngine(this);
flutterEngine.getDartExecutor().executeDartEntrypoint(
    DartExecutor.DartEntrypoint.createDefault()
);
FlutterEngineCache
    .getInstance()
    .put("my_engine_id", flutterEngine);
flutterEngine.getNavigationChannel().setInitialRoute("/");

    
    MethodChannel mc=new 
    MethodChannel(flutterEngine.getDartExecutor().getBinaryMessenger(),CHANNEL);
    mc.setMethodCallHandler((methodCall, result) ->
        {
            if(methodCall.method.equals("test"))
            {
                result.success("Hai from android and this is the data yopu sent me "+ methodCall.argument("data"));
//Accessing data sent from flutter
            }
            else
            {
                Log.i("new method came",methodCall.method);
            }

        }
    );

use this blog to know more

https://medium.com/@andymobitec/flutter-sending-data-between-android-and-flutter-1e0693fbae64

Answer 2

You can pass data with method channel, Yes I am late for answer but it might be useful for other devs.

In native you need to invoke method channel, below is example of android.

val testChannel = MethodChannel(flutterEngine!!.dartExecutor.binaryMessenger, "method_channel_name")
            testChannel.invokeMethod("method_name", referrerUrl);

In Flutter you can listen this invoked method.

static const platform = const MethodChannel('method_channel_name');
platform.setMethodCallHandler((call)async{
      // you can get hear method and passed arguments with method 
      print("init state setMethodCallHandler ${call.arguments}");
    });