Initial Commit for PlaformChannel Sample App (#453)

platform_channels/lib/src/method_channel_demo.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:platform_channels/src/counter_method_channel.dart';
+
+/// The widget demonstrates how to use [MethodChannel] to invoke platform methods.
+/// It has two [RaisedButton]s to increment and decrement the value of
+/// [count], and a [Text] widget to display its value.
+class MethodChannelDemo extends StatefulWidget {
+  @override
+  _MethodChannelDemoState createState() => _MethodChannelDemoState();
+}
+
+class _MethodChannelDemoState extends State<MethodChannelDemo> {
+  int count = 0;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('MethodChannel Demo'),
+      ),
+      body: Builder(
+        builder: (context) {
+          return Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: [
+              Text(
+                'Value of count is $count',
+                style: Theme.of(context).textTheme.headline5,
+              ),
+              SizedBox(
+                height: 16,
+              ),
+              Row(
+                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+                children: [
+                  // Whenever users press the RaisedButton, it invokes
+                  // Counter.increment method to increment the value of count.
+                  RaisedButton.icon(
+                    onPressed: () async {
+                      try {
+                        final value =
+                            await Counter.increment(counterValue: count);
+                        setState(() => count = value);
+                      } catch (error) {
+                        showErrorMessage(
+                          context,
+                          error.message as String,
+                        );
+                      }
+                    },
+                    icon: Icon(Icons.add),
+                    label: Text('Increment'),
+                  ),
+
+                  // Whenever users press the RaisedButton, it invokes
+                  // Counter.decrement method to decrement the value of count.
+                  RaisedButton.icon(
+                    onPressed: () async {
+                      try {
+                        final value =
+                            await Counter.decrement(counterValue: count);
+                        setState(() => count = value);
+                      } catch (error) {
+                        showErrorMessage(
+                          context,
+                          error.message as String,
+                        );
+                      }
+                    },
+                    icon: Icon(Icons.remove),
+                    label: Text('Decrement'),
+                  )
+                ],
+              )
+            ],
+          );
+        },
+      ),
+    );
+  }
+
+  void showErrorMessage(BuildContext context, String errorMessage) {
+    Scaffold.of(context).showSnackBar(SnackBar(
+      content: Text(errorMessage),
+    ));
+  }
+}