[platform_channels] adds Platform Image demo (#475)

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

@@ -9,8 +9,11 @@ import android.hardware.Sensor
 import android.hardware.SensorManager
 import io.flutter.embedding.android.FlutterActivity
 import io.flutter.embedding.engine.FlutterEngine
+import io.flutter.plugin.common.BasicMessageChannel
 import io.flutter.plugin.common.EventChannel
 import io.flutter.plugin.common.MethodChannel
+import io.flutter.plugin.common.StandardMessageCodec
+import java.io.InputStream
 
 class MainActivity : FlutterActivity() {
     override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
@@ -40,5 +43,15 @@ class MainActivity : FlutterActivity() {
         val accelerometerSensor: Sensor = sensorManger.getDefaultSensor(Sensor.TYPE_ACCELEROMETER)
         EventChannel(flutterEngine.dartExecutor, "eventChannelDemo")
                 .setStreamHandler(AccelerometerStreamHandler(sensorManger, accelerometerSensor))
+
+        // Registers a MessageHandler for BasicMessageChannel to receive a message from Dart and send
+        // image data in reply.
+        BasicMessageChannel(flutterEngine.dartExecutor, "platformImageDemo", StandardMessageCodec())
+                .setMessageHandler { message, reply ->
+                    if (message == "getImage") {
+                        val inputStream: InputStream = assets.open("eat_new_orleans.jpg")
+                        reply.reply(inputStream.readBytes());
+                    }
+                }
     }
 }

platform_channels/lib/main.dart

@@ -5,6 +5,7 @@
 import 'package:flutter/material.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';
 
 void main() {
   runApp(PlatformChannelSample());
@@ -17,6 +18,7 @@ class PlatformChannelSample extends StatelessWidget {
       routes: {
         '/methodChannelDemo': (context) => MethodChannelDemo(),
         '/eventChannelDemo': (context) => EventChannelDemo(),
+        '/platformImageDemo': (context) => PlatformImageDemo(),
       },
       title: 'Platform Channel Sample',
       home: HomePage(),
@@ -41,6 +43,10 @@ List<DemoInfo> demoList = [
   DemoInfo(
     'EventChannel Demo',
     '/eventChannelDemo',
+  ),
+  DemoInfo(
+    'Platform Image Demo',
+    '/platformImageDemo',
   )
 ];
 

platform_channels/lib/src/image_basic_message_channel.dart

@@ -0,0 +1,28 @@
+// 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:typed_data';
+
+import 'package:flutter/services.dart';
+
+/// This class manages a [BasicMessageChannel] that can return an image loaded
+/// from a native asset. The [BasicMessageChannel] uses [StandardMessageCodec]
+/// since it supports [Uint8List], which is used to transport the image data.
+class PlatformImageFetcher {
+  static final _basicMessageChannel = const BasicMessageChannel<dynamic>(
+      'platformImageDemo', StandardMessageCodec());
+
+  /// Method responsible for providing the platform image.
+  static Future<Uint8List> getImage() async {
+    final reply = await _basicMessageChannel.send('getImage') as Uint8List;
+    if (reply == null) {
+      throw PlatformException(
+        code: 'Error',
+        message: 'Failed to load Platform Image',
+        details: null,
+      );
+    }
+    return reply;
+  }
+}

platform_channels/lib/src/platform_image_demo.dart

@@ -0,0 +1,76 @@
+// 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:typed_data';
+
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:platform_channels/src/image_basic_message_channel.dart';
+
+/// Demonstrates how to use [BasicMessageChannel] to get an image from platform.
+///
+/// The widget uses [Image.memory] to display the image obtained from the
+/// platform.
+class PlatformImageDemo extends StatefulWidget {
+  @override
+  _PlatformImageDemoState createState() => _PlatformImageDemoState();
+}
+
+class _PlatformImageDemoState extends State<PlatformImageDemo> {
+  Future<Uint8List> imageData;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text('Platform Image Demo'),
+      ),
+      body: Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            Flexible(
+              child: FractionallySizedBox(
+                widthFactor: 1,
+                heightFactor: 0.6,
+                child: FutureBuilder<Uint8List>(
+                  future: imageData,
+                  builder: (context, snapshot) {
+                    if (snapshot.connectionState == ConnectionState.none) {
+                      return Placeholder();
+                    } else if (snapshot.hasError) {
+                      return Center(
+                        child: Text(snapshot.error.toString()),
+                      );
+                    } else if (snapshot.connectionState ==
+                        ConnectionState.done) {
+                      return Image.memory(
+                        snapshot.data,
+                        fit: BoxFit.fill,
+                      );
+                    }
+                    return CircularProgressIndicator();
+                  },
+                ),
+              ),
+            ),
+            SizedBox(
+              height: 16,
+            ),
+            RaisedButton(
+              onPressed: imageData != null
+                  ? null
+                  : () {
+                      setState(() {
+                        imageData = PlatformImageFetcher.getImage();
+                      });
+                    },
+              child: Text('Get Image'),
+            )
+          ],
+        ),
+      ),
+    );
+  }
+}

platform_channels/pubspec.yaml

@@ -20,3 +20,5 @@ dev_dependencies:
 
 flutter:
   uses-material-design: true
+  assets:
+    - assets/

platform_channels/test/src/platform_image_demo_test.dart

@@ -0,0 +1,38 @@
+// 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/platform_image_demo.dart';
+
+void main() {
+  group('Platform Image Demo tests', () {
+    setUpAll(() {
+      // Register a mock for MessageHandler.
+      BasicMessageChannel<dynamic>('platformImageDemo', StandardMessageCodec())
+          .setMockMessageHandler((dynamic message) async {
+        var byteData = await rootBundle.load('assets/eat_new_orleans.jpg');
+        return byteData.buffer.asUint8List();
+      });
+    });
+
+    testWidgets('Platform Image test', (tester) async {
+      await tester.pumpWidget(MaterialApp(
+        home: PlatformImageDemo(),
+      ));
+
+      // Initially a PlaceHolder is displayed when imageData is null.
+      expect(find.byType(Placeholder), findsOneWidget);
+      expect(find.byType(Image), findsNothing);
+
+      // Tap on RaisedButton to get Image.
+      await tester.tap(find.byType(RaisedButton));
+      await tester.pumpAndSettle();
+
+      expect(find.byType(Placeholder), findsNothing);
+      expect(find.byType(Image), findsOneWidget);
+    });
+  });
+}