[platform_channels] adds BasicMessageChannel Demo (#484)

platform_channels/android/app/build.gradle

@@ -60,4 +60,5 @@ flutter {
 
 dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
+    implementation 'com.google.code.gson:gson:2.8.6'
 }

platform_channels/android/app/src/main/kotlin/dev/flutter/platform_channels/MainActivity.kt

@@ -7,13 +7,13 @@ package dev.flutter.platform_channels
 import android.content.Context
 import android.hardware.Sensor
 import android.hardware.SensorManager
+import com.google.gson.Gson
+import com.google.gson.reflect.TypeToken
 import io.flutter.embedding.android.FlutterActivity
 import io.flutter.embedding.engine.FlutterEngine
-import io.flutter.plugin.common.BasicMessageChannel
+import io.flutter.plugin.common.*
-import io.flutter.plugin.common.EventChannel
-import io.flutter.plugin.common.MethodChannel
-import io.flutter.plugin.common.StandardMessageCodec
 import java.io.InputStream
+import java.nio.ByteBuffer
 
 class MainActivity : FlutterActivity() {
     override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
@@ -50,7 +50,38 @@ class MainActivity : FlutterActivity() {
                 .setMessageHandler { message, reply ->
                     if (message == "getImage") {
                         val inputStream: InputStream = assets.open("eat_new_orleans.jpg")
-                        reply.reply(inputStream.readBytes());
+                        reply.reply(inputStream.readBytes())
+                    }
+                }
+
+        val petList = mutableListOf<Map<String, String>>()
+        val gson = Gson()
+
+        // A BasicMessageChannel for sending petList to Dart.
+        val stringCodecChannel = BasicMessageChannel(flutterEngine.dartExecutor, "stringCodecDemo", StringCodec.INSTANCE)
+
+        // Registers a MessageHandler for BasicMessageChannel to receive pet details to be
+        // added in petList and send the it back to Dart using stringCodecChannel.
+        BasicMessageChannel(flutterEngine.dartExecutor, "jsonMessageCodecDemo", JSONMessageCodec.INSTANCE)
+                .setMessageHandler { message, reply ->
+                    petList.add(0, gson.fromJson(message.toString(), object : TypeToken<Map<String, String>>() {}.type))
+                    stringCodecChannel.send(gson.toJson(mapOf("petList" to petList)))
+                }
+
+        // Registers a MessageHandler for BasicMessageChannel to receive the index of pet
+        // details to be removed from the petList and send the petList back to Dart using
+        // stringCodecChannel. If the index is not in the range of petList, we send null
+        // back to Dart.
+        BasicMessageChannel(flutterEngine.dartExecutor, "binaryCodecDemo", BinaryCodec.INSTANCE)
+                .setMessageHandler { message, reply ->
+                    val index = String(message!!.array()).toInt()
+                    if (index >= 0 && index < petList.size) {
+                        petList.removeAt(index)
+                        val replyMessage = "Removed Successfully"
+                        reply.reply(ByteBuffer.allocateDirect(replyMessage.toByteArray().size).put(replyMessage.toByteArray()))
+                        stringCodecChannel.send(gson.toJson(mapOf("petList" to petList)))
+                    } else {
+                        reply.reply(null)
                     }
                 }
     }

platform_channels/lib/main.dart

@@ -3,6 +3,8 @@
 // found in the LICENSE file.
 
 import 'package:flutter/material.dart';
+import 'package:platform_channels/src/add_pet_details.dart';
+import 'package:platform_channels/src/pet_list_screen.dart';
 import 'package:platform_channels/src/event_channel_demo.dart';
 import 'package:platform_channels/src/method_channel_demo.dart';
 import 'package:platform_channels/src/platform_image_demo.dart';
@@ -19,6 +21,8 @@ class PlatformChannelSample extends StatelessWidget {
         '/methodChannelDemo': (context) => MethodChannelDemo(),
         '/eventChannelDemo': (context) => EventChannelDemo(),
         '/platformImageDemo': (context) => PlatformImageDemo(),
+        '/petListScreen': (context) => PetListScreen(),
+        '/addPetDetails': (context) => AddPetDetails(),
       },
       title: 'Platform Channel Sample',
       home: HomePage(),
@@ -47,6 +51,10 @@ List<DemoInfo> demoList = [
   DemoInfo(
     'Platform Image Demo',
     '/platformImageDemo',
+  ),
+  DemoInfo(
+    'BasicMessageChannel Demo',
+    '/petListScreen',
   )
 ];
 

platform_channels/lib/src/add_pet_details.dart

@@ -0,0 +1,86 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:platform_channels/src/pet_list_message_channel.dart';
+
+/// Demonstrates how to use [BasicMessageChannel] to send a message to platform.
+///
+/// The widget uses [TextField] and [RadioListTile] to take the [PetDetails.breed] and
+/// [PetDetails.petType] from the user respectively.
+class AddPetDetails extends StatefulWidget {
+  @override
+  _AddPetDetailsState createState() => _AddPetDetailsState();
+}
+
+class _AddPetDetailsState extends State<AddPetDetails> {
+  final breedTextController = TextEditingController();
+  String petType = 'Dog';
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text('Add Pet Details'),
+        actions: <Widget>[
+          IconButton(
+            icon: Icon(Icons.add),
+            onPressed: () {
+              PetListMessageChannel.addPetDetails(
+                PetDetails(
+                  petType: petType,
+                  breed: breedTextController.text,
+                ),
+              );
+
+              Navigator.pop(context);
+            },
+          )
+        ],
+      ),
+      body: Padding(
+        padding: const EdgeInsets.all(8.0),
+        child: Column(
+          children: [
+            SizedBox(
+              height: 8,
+            ),
+            TextField(
+              controller: breedTextController,
+              decoration: InputDecoration(
+                border: OutlineInputBorder(),
+                filled: true,
+                hintText: 'Breed of pet',
+                labelText: 'Breed',
+              ),
+            ),
+            SizedBox(
+              height: 8,
+            ),
+            RadioListTile<String>(
+              title: const Text('Dog'),
+              value: 'Dog',
+              groupValue: petType,
+              onChanged: (value) {
+                setState(() {
+                  petType = value;
+                });
+              },
+            ),
+            RadioListTile<String>(
+              title: const Text('Cat'),
+              value: 'Cat',
+              groupValue: petType,
+              onChanged: (value) {
+                setState(() {
+                  petType = value;
+                });
+              },
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

platform_channels/lib/src/pet_list_message_channel.dart

@@ -0,0 +1,84 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:convert';
+
+import 'package:flutter/services.dart';
+
+/// This class includes two methods [addPetDetails] and [removePet] which are used
+/// to add a new pet and remove a pet from the the list respectively.
+class PetListMessageChannel {
+  static final _jsonMessageCodecChannel =
+      BasicMessageChannel<dynamic>('jsonMessageCodecDemo', JSONMessageCodec());
+
+  static final _binaryCodecChannel =
+      BasicMessageChannel('binaryCodecDemo', BinaryCodec());
+
+  /// Method to add a new pet to the list.
+  ///
+  /// Demonstrates how to use [BasicMessageChannel] and [JSONMessageCodec] to
+  /// send more structured data to platform like a [Map] in this case.
+  static void addPetDetails(PetDetails petDetails) {
+    _jsonMessageCodecChannel.send(petDetails.toJson());
+  }
+
+  /// Method to remove a pet from the list.
+  ///
+  /// Demonstrates how to use [BasicMessageChannel] and [BinaryCodec] to
+  /// send [ByteData] to platform. If the reply received is null, then
+  /// we will throw a [PlatformException].
+  static Future<void> removePet(int index) async {
+    final uInt8List = utf8.encoder.convert(index.toString());
+    final reply = await _binaryCodecChannel.send(uInt8List.buffer.asByteData());
+    if (reply == null) {
+      throw PlatformException(
+        code: 'INVALID INDEX',
+        message: 'Failed to delete pet details',
+        details: null,
+      );
+    }
+  }
+}
+
+/// A model class that provides [petList] which is received from platform.
+class PetListModel {
+  PetListModel({
+    this.petList,
+  });
+
+  final List<PetDetails> petList;
+
+  /// Method that maps the incoming string of json object to List of [PetDetails].
+  factory PetListModel.fromJson(String jsonString) {
+    final jsonData = json.decode(jsonString) as Map<String, dynamic>;
+    return PetListModel(
+      petList: List.from((jsonData['petList'] as List).map<PetDetails>(
+        (dynamic petDetailsMap) => PetDetails.fromMap(
+          petDetailsMap as Map<String, dynamic>,
+        ),
+      )),
+    );
+  }
+}
+
+/// A simple model that provides pet details like [petType] and [breed] of pet.
+class PetDetails {
+  PetDetails({
+    this.petType,
+    this.breed,
+  });
+
+  final String petType;
+  final String breed;
+
+  factory PetDetails.fromMap(Map<String, dynamic> map) => PetDetails(
+        petType: map['petType'] as String,
+        breed: map['breed'] as String,
+      );
+
+  Map<String, String> toJson() => <String, String>{
+        'petType': petType,
+        'breed': breed,
+      };
+}

platform_channels/lib/src/pet_list_screen.dart

@@ -0,0 +1,91 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:platform_channels/src/pet_list_message_channel.dart';
+
+/// Demonstrates how to use [BasicMessageChannel] to send & receive the platform
+/// Message.
+class PetListScreen extends StatefulWidget {
+  @override
+  _PetListScreenState createState() => _PetListScreenState();
+}
+
+class _PetListScreenState extends State<PetListScreen> {
+  PetListModel petListModel;
+
+  @override
+  void initState() {
+    super.initState();
+    // Receives a string of json object from the platform and converts it
+    // to PetModel.
+    BasicMessageChannel('stringCodecDemo', StringCodec())
+        .setMessageHandler((message) async {
+      setState(() {
+        petListModel = PetListModel.fromJson(message);
+      });
+      return;
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text('Pet List'),
+      ),
+      floatingActionButton: FloatingActionButton(
+        child: Icon(Icons.add),
+        onPressed: () {
+          Navigator.pushNamed(context, '/addPetDetails');
+        },
+      ),
+      body: petListModel?.petList?.isEmpty ?? true
+          ? Center(child: Text('Enter Pet Details'))
+          : BuildPetList(petListModel.petList),
+    );
+  }
+}
+
+/// Shows list of [PetDetails].
+class BuildPetList extends StatelessWidget {
+  final List<PetDetails> petList;
+
+  BuildPetList(this.petList);
+
+  @override
+  Widget build(BuildContext context) {
+    return ListView.builder(
+      padding: EdgeInsets.all(8),
+      itemCount: petList.length,
+      itemBuilder: (context, index) {
+        return ListTile(
+          title: Text('Pet breed: ${petList[index].breed}'),
+          subtitle: Text(
+            'Pet type: ${petList[index].petType}',
+          ),
+          trailing: IconButton(
+            icon: Icon(Icons.delete),
+            onPressed: () async {
+              try {
+                await PetListMessageChannel.removePet(index);
+                showSnackBar('Removed successfully!', context);
+              } catch (error) {
+                showSnackBar(error.message.toString(), context);
+              }
+            },
+          ),
+        );
+      },
+    );
+  }
+
+  void showSnackBar(String message, BuildContext context) {
+    Scaffold.of(context).showSnackBar(SnackBar(
+      backgroundColor: Theme.of(context).primaryColor,
+      content: Text(message),
+    ));
+  }
+}

platform_channels/test/src/add_pet_details_test.dart

@@ -0,0 +1,37 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:platform_channels/src/add_pet_details.dart';
+
+void main() {
+  group('AddPetDetails tests', () {
+    var petList = <Map>[];
+
+    setUpAll(() {
+      BasicMessageChannel<dynamic>('jsonMessageCodecDemo', JSONMessageCodec())
+          .setMockMessageHandler((dynamic message) async {
+        petList.add(message as Map);
+      });
+    });
+
+    testWidgets('Enter pet details', (tester) async {
+      await tester.pumpWidget(MaterialApp(home: AddPetDetails()));
+
+      // Enter the breed of cat.
+      await tester.enterText(find.byType(TextField), 'Persian');
+      // Select cat from the pet type.
+      await tester.tap(find.text('Cat'));
+
+      // Initially the list will be empty.
+      expect(petList, isEmpty);
+      await tester.tap(find.byIcon(Icons.add));
+
+      expect(petList, isNotEmpty);
+      expect(petList.last['breed'], 'Persian');
+    });
+  });
+}

platform_channels/test/src/pet_list_screen_test.dart

@@ -0,0 +1,83 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:convert';
+
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:platform_channels/src/pet_list_message_channel.dart';
+import 'package:platform_channels/src/pet_list_screen.dart';
+
+void main() {
+  group('PetListScreen tests', () {
+    final basicMessageChannel =
+        BasicMessageChannel('stringCodecDemo', StringCodec());
+
+    var petList = [
+      {
+        'petType': 'Dog',
+        'breed': 'Pug',
+      }
+    ];
+
+    PetListModel petListModel;
+
+    setUpAll(() {
+      // Mock for the pet list received from the platform.
+      basicMessageChannel.setMockMessageHandler((message) async {
+        petListModel = PetListModel.fromJson(message);
+        return;
+      });
+
+      // Mock for the index received from the Dart to delete the pet details,
+      // and send the updated pet list back to Dart.
+      BasicMessageChannel('binaryCodecDemo', BinaryCodec())
+          .setMockMessageHandler((message) async {
+        // Convert the ByteData to String.
+        final index = utf8.decoder.convert(message.buffer
+            .asUint8List(message.offsetInBytes, message.lengthInBytes));
+
+        // Remove the pet details at the given index.
+        petList.removeAt(int.parse(index));
+
+        // Send the updated petList back.
+        final map = {'petList': petList};
+        await basicMessageChannel.send(json.encode(map));
+        return;
+      });
+    });
+
+    test('convert json message to PetListModel', () {
+      TestWidgetsFlutterBinding.ensureInitialized();
+
+      // Initially petListModel will be null.
+      expect(petListModel, isNull);
+
+      // Send the pet list using BasicMessageChannel.
+      final map = {'petList': petList};
+      basicMessageChannel.send(json.encode(map));
+
+      // Get the details of first pet.
+      final petDetails = petListModel.petList.first;
+      expect(petDetails.petType, 'Dog');
+      expect(petDetails.breed, 'Pug');
+    });
+
+    testWidgets('BuildPetList test', (tester) async {
+      await tester.pumpWidget(MaterialApp(
+        home: Scaffold(
+          body: BuildPetList(petListModel.petList),
+        ),
+      ));
+
+      expect(find.text('Pet type: Dog'), findsOneWidget);
+      expect(find.text('Pet breed: Pug'), findsOneWidget);
+
+      // Delete the pet details.
+      await tester.tap(find.byIcon(Icons.delete).first);
+      expect(petListModel.petList, isEmpty);
+    });
+  });
+}