[platform_channels] adds BasicMessageChannel Demo (#484)

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),
+    ));
+  }
+}