[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;
+                });
+              },
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}