Update Android part of flutter_view to use the new platform message c… (#8729)

* update Android part of flutter_view to use the new platform message channel.

* addressed comments

* addressed comments

examples/flutter_view/android/app/src/main/java/com/example/view/MainActivity.java

@@ -6,6 +6,10 @@ import android.support.design.widget.FloatingActionButton;
 import android.support.v7.app.AppCompatActivity;
 import android.view.View;
 import android.widget.TextView;
+import io.flutter.plugin.common.FlutterMessageChannel;
+import io.flutter.plugin.common.FlutterMessageChannel.MessageHandler;
+import io.flutter.plugin.common.FlutterMessageChannel.Reply;
+import io.flutter.plugin.common.StringMessageCodec;
 import io.flutter.view.FlutterMain;
 import io.flutter.view.FlutterView;
 import java.util.ArrayList;
@@ -15,6 +19,8 @@ public class MainActivity extends AppCompatActivity {
     private int counter;
     private static final String CHANNEL = "increment";
     private static final String EMPTY_MESSAGE = "";
+    private static final String PING = "ping";
+    private FlutterMessageChannel messageChannel;
 
     private String[] getArgsFromIntent(Intent intent) {
         // Before adding more entries to this list, consider that arbitrary
@@ -51,11 +57,15 @@ public class MainActivity extends AppCompatActivity {
         flutterView = (FlutterView) findViewById(R.id.flutter_view);
         flutterView.runFromBundle(FlutterMain.findAppBundlePath(getApplicationContext()), null);
 
-        flutterView.addOnMessageListener(CHANNEL,
-            new FlutterView.OnMessageListener() {
+        messageChannel =
+            new FlutterMessageChannel<String>(flutterView, CHANNEL, StringMessageCodec.INSTANCE);
+        messageChannel.
+            setMessageHandler(new MessageHandler<String>() {
                 @Override
-                public String onMessage(FlutterView view, String message) {
-                    return onFlutterIncrement();
+                public void onMessage(String s, Reply<String> reply) {
+                    onFlutterIncrement();
+                    reply.send(EMPTY_MESSAGE);
+
                 }
             });
 
@@ -69,15 +79,14 @@ public class MainActivity extends AppCompatActivity {
     }
 
     private void sendAndroidIncrement() {
-        flutterView.sendToFlutter(CHANNEL, EMPTY_MESSAGE, null);
+        messageChannel.send(PING);
     }
 
-    private String onFlutterIncrement() {
+    private void onFlutterIncrement() {
         counter++;
         TextView textView = (TextView) findViewById(R.id.button_tap);
         String value = "Flutter button tapped " + counter + (counter == 1 ? " time" : " times");
         textView.setText(value);
-        return EMPTY_MESSAGE;
     }
 
     @Override

examples/flutter_view/lib/main.dart

@@ -31,29 +31,32 @@ class MyHomePage extends StatefulWidget {
 
 class _MyHomePageState extends State<MyHomePage> {
   static const String _channel = "increment";
+  static const String _pong = "pong";
   static const String _emptyMessage = "";
+  static const PlatformMessageChannel<String> platform =
+      const PlatformMessageChannel<String>(_channel, const StringCodec());
 
   int _counter = 0;
 
-  Future<String> handlePlatformIncrement(String message) async {
-    _incrementCounter();
-    return _emptyMessage;
+  @override
+  void initState() {
+    super.initState();
+    platform.setMessageHandler(_handlePlatformIncrement);
   }
 
-  void _incrementCounter() {
+  Future<String> _handlePlatformIncrement(String message) async {
     setState(() {
       _counter++;
     });
+    return _emptyMessage;
   }
 
   void _sendFlutterIncrement() {
-    PlatformMessages.sendString(_channel, _emptyMessage);
+    platform.send(_pong);
   }
 
   @override
   Widget build(BuildContext context) {
-    PlatformMessages.setStringMessageHandler(_channel,
-                                             handlePlatformIncrement);
     return new Scaffold(
       body: new Column(
         crossAxisAlignment: CrossAxisAlignment.start,