Android implmentation works.

.gitignore

@@ -1 +1,8 @@
-src/node_modules
+.vscode/
+
+src/node_modules
+src/android/.settings/
+src/android/.project
+src/android/app/.project
+src/android/app/.classpath
+src/android/app/.settings/

src/android/app/src/debug/AndroidManifest.xml

@@ -4,7 +4,9 @@
     <!-- Flutter needs it to communicate with the running application
          to allow setting breakpoints, to provide hot reload, etc.
     -->
+
     <uses-permission android:name="android.permission.INTERNET"/>
+	<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>
 
 	<application
   		android:usesCleartextTraffic="true"

src/android/app/src/main/AndroidManifest.xml

@@ -32,5 +32,11 @@
                 <category android:name="android.intent.category.LAUNCHER"/>
             </intent-filter>
         </activity>
+
+		<activity
+			android:name=".MyReactActivity"
+			android:label="rnflutter"
+			android:theme="@style/Theme.AppCompat.Light.NoActionBar">
+		</activity>
     </application>
 </manifest>

src/android/app/src/main/java/com/example/rnflutter/MainActivity.java

@@ -1,13 +1,64 @@
 package com.example.rnflutter;
 
+import android.content.Intent;
+import android.net.Uri;
+import android.os.Build;
 import android.os.Bundle;
+import android.provider.Settings;
+import android.widget.Toast;
+
 import io.flutter.app.FlutterActivity;
 import io.flutter.plugins.GeneratedPluginRegistrant;
+import io.flutter.plugin.common.MethodCall;
+import io.flutter.plugin.common.MethodChannel;
+import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
+import io.flutter.plugin.common.MethodChannel.Result;
 
 public class MainActivity extends FlutterActivity {
-  @Override
-  protected void onCreate(Bundle savedInstanceState) {
-    super.onCreate(savedInstanceState);
-    GeneratedPluginRegistrant.registerWith(this);
-  }
+
+	private final int OVERLAY_PERMISSION_REQ_CODE = 1;  // Choose any value
+
+	@Override
+	protected void onCreate(Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+
+		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { // Only for development
+			if (!Settings.canDrawOverlays(this)) {
+				Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + getPackageName()));
+				startActivityForResult(intent, OVERLAY_PERMISSION_REQ_CODE);
+			}
+		}
+
+		new MethodChannel(getFlutterView(), "main_channel").setMethodCallHandler(
+			new MethodCallHandler() {
+				@Override
+				public void onMethodCall(MethodCall call, Result result) {
+				switch (call.method) {
+					case "startRNActivity":
+						result.success(null);
+						Intent intent = new Intent(MainActivity.this, MyReactActivity.class);
+						startActivity(intent);
+						break;
+					default:
+						result.notImplemented();
+				}
+				}
+			}
+		);
+
+		GeneratedPluginRegistrant.registerWith(this);
+	}
+
+	@Override
+	protected void onActivityResult(int requestCode, int resultCode, Intent data) {
+		if (requestCode == OVERLAY_PERMISSION_REQ_CODE) { // Only for development 
+			if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+				if (!Settings.canDrawOverlays(this)) {
+					Toast.makeText(this, "SYSTEM_ALERT_WINDOW permission not granted", Toast.LENGTH_LONG).show();
+					// SYSTEM_ALERT_WINDOW permission not granted
+				}
+			}
+		}
+		//mReactInstanceManager.onActivityResult( this, requestCode, resultCode, data );
+	}
 }

src/android/app/src/main/java/com/example/rnflutter/MyReactActivity.java

@@ -0,0 +1,91 @@
+package com.example.rnflutter;
+
+import android.app.Activity;
+import android.os.Bundle;
+import android.view.KeyEvent;
+
+import com.facebook.react.ReactInstanceManager;
+import com.facebook.react.ReactRootView;
+import com.facebook.react.common.LifecycleState;
+import com.facebook.react.modules.core.DefaultHardwareBackBtnHandler;
+import com.facebook.react.shell.MainReactPackage;
+
+public class MyReactActivity extends Activity implements DefaultHardwareBackBtnHandler {
+
+    private ReactRootView mReactRootView;
+    private ReactInstanceManager mReactInstanceManager;
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+
+        mReactRootView = new ReactRootView(this);
+        mReactInstanceManager = ReactInstanceManager.builder()
+                .setApplication(getApplication())
+                .setCurrentActivity(this)
+                .setBundleAssetName("index.android.bundle")
+                .setJSMainModulePath("index")
+                .addPackage(new MainReactPackage())
+                .setUseDeveloperSupport(BuildConfig.DEBUG)
+                .setInitialLifecycleState(LifecycleState.RESUMED)
+                .build();
+        // The string here (e.g. "MyReactNativeApp") has to match
+        // the string in AppRegistry.registerComponent() in index.js
+        mReactRootView.startReactApplication(mReactInstanceManager, "RNFlutter", null);
+
+        setContentView(mReactRootView);
+    }
+
+    @Override
+    public void invokeDefaultOnBackPressed() {
+        super.onBackPressed();
+    }
+
+    @Override
+    protected void onPause() {
+        super.onPause();
+
+        if (mReactInstanceManager != null) {
+            mReactInstanceManager.onHostPause(this);
+        }
+    }
+
+    @Override
+    protected void onResume() {
+        super.onResume();
+
+        if (mReactInstanceManager != null) {
+            mReactInstanceManager.onHostResume(this, this);
+        }
+    }
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+
+        if (mReactInstanceManager != null) {
+            mReactInstanceManager.onHostDestroy(this);
+        }
+        if (mReactRootView != null) {
+            mReactRootView.unmountReactApplication();
+        }
+    }
+
+    @Override
+    public void onBackPressed() {
+        if (mReactInstanceManager != null) {
+            mReactInstanceManager.onBackPressed();
+        } else {
+            super.onBackPressed();
+        }
+    }
+
+    @Override
+    public boolean onKeyUp(int keyCode, KeyEvent event) {
+        if (keyCode == KeyEvent.KEYCODE_MENU && mReactInstanceManager != null) {
+            mReactInstanceManager.showDevOptionsDialog();
+            return true;
+        }
+        return super.onKeyUp(keyCode, event);
+    }
+}

src/index.js

@@ -0,0 +1,26 @@
+import React from "react";
+import {AppRegistry, StyleSheet, Text, View} from "react-native";
+
+class RNFlutter extends React.Component {
+  render() {
+	return (
+	  <View style={styles.container}>
+		<Text style={styles.hello}>Hello from React Native and Flutter!</Text>
+	  </View>
+	);
+  }
+}
+
+var styles = StyleSheet.create({
+  container: {
+	flex: 1,
+	justifyContent: "center",
+  },
+  hello: {
+	fontSize: 20,
+	textAlign: "center",
+	margin: 10,
+  },
+});
+
+AppRegistry.registerComponent("RNFlutter", () => RNFlutter);

src/lib/main.dart

@@ -1,23 +1,14 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 
 void main() => runApp(MyApp());
 
 class MyApp extends StatelessWidget {
-  // This widget is the root of your application.
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
       title: 'Flutter Demo',
       theme: ThemeData(
-        // This is the theme of your application.
-        //
-        // Try running your application with "flutter run". You'll see the
-        // application has a blue toolbar. Then, without quitting the app, try
-        // changing the primarySwatch below to Colors.green and then invoke
-        // "hot reload" (press "r" in the console where you ran "flutter run",
-        // or simply save your changes to "hot reload" in a Flutter IDE).
-        // Notice that the counter didn't reset back to zero; the application
-        // is not restarted.
         primarySwatch: Colors.blue,
       ),
       home: MyHomePage(title: 'Flutter Demo Home Page'),
@@ -27,68 +18,31 @@ class MyApp extends StatelessWidget {
 
 class MyHomePage extends StatefulWidget {
   MyHomePage({Key key, this.title}) : super(key: key);
-
-  // This widget is the home page of your application. It is stateful, meaning
-  // that it has a State object (defined below) that contains fields that affect
-  // how it looks.
-
-  // This class is the configuration for the state. It holds the values (in this
-  // case the title) provided by the parent (in this case the App widget) and
-  // used by the build method of the State. Fields in a Widget subclass are
-  // always marked "final".
-
   final String title;
 
   @override
   _MyHomePageState createState() => _MyHomePageState();
 }
 
 class _MyHomePageState extends State<MyHomePage> {
+
   int _counter = 0;
+  static const MethodChannel _channel = const MethodChannel("main_channel");
 
   void _incrementCounter() {
     setState(() {
-      // This call to setState tells the Flutter framework that something has
-      // changed in this State, which causes it to rerun the build method below
-      // so that the display can reflect the updated values. If we changed
-      // _counter without calling setState(), then the build method would not be
-      // called again, and so nothing would appear to happen.
       _counter++;
     });
   }
 
   @override
   Widget build(BuildContext context) {
-    // This method is rerun every time setState is called, for instance as done
-    // by the _incrementCounter method above.
-    //
-    // The Flutter framework has been optimized to make rerunning build methods
-    // fast, so that you can just rebuild anything that needs updating rather
-    // than having to individually change instances of widgets.
     return Scaffold(
       appBar: AppBar(
-        // Here we take the value from the MyHomePage object that was created by
-        // the App.build method, and use it to set our appbar title.
         title: Text(widget.title),
       ),
       body: Center(
-        // Center is a layout widget. It takes a single child and positions it
-        // in the middle of the parent.
         child: Column(
-          // Column is also layout widget. It takes a list of children and
-          // arranges them vertically. By default, it sizes itself to fit its
-          // children horizontally, and tries to be as tall as its parent.
-          //
-          // Invoke "debug painting" (press "p" in the console, choose the
-          // "Toggle Debug Paint" action from the Flutter Inspector in Android
-          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
-          // to see the wireframe for each widget.
-          //
-          // Column has various properties to control how it sizes itself and
-          // how it positions its children. Here we use mainAxisAlignment to
-          // center the children vertically; the main axis here is the vertical
-          // axis because Columns are vertical (the cross axis would be
-          // horizontal).
           mainAxisAlignment: MainAxisAlignment.center,
           children: <Widget>[
             Text(
@@ -98,14 +52,30 @@ class _MyHomePageState extends State<MyHomePage> {
               '$_counter',
               style: Theme.of(context).textTheme.display1,
             ),
+            MaterialButton(
+                    child: const Text('Open Screen'),
+                    elevation: 5.0,
+                    color: Colors.blue,
+                    textColor: Colors.white,
+                    onPressed: () {
+                      _getNewActivity();
+                    }),
           ],
         ),
       ),
       floatingActionButton: FloatingActionButton(
         onPressed: _incrementCounter,
         tooltip: 'Increment',
         child: Icon(Icons.add),
-      ), // This trailing comma makes auto-formatting nicer for build methods.
+      ),
     );
   }
+
+  _getNewActivity() async {
+    try {
+      await _channel.invokeMethod('startRNActivity');
+    } on PlatformException catch (e) {
+      print(e.message);
+    }
+  }
 }