[platform_channels] adds EventChannel Demo (#462)

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

@@ -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.
+
+package dev.flutter.platform_channels
+
+import android.hardware.Sensor
+import android.hardware.SensorEvent
+import android.hardware.SensorEventListener
+import android.hardware.SensorManager
+import io.flutter.plugin.common.EventChannel
+
+class AccelerometerStreamHandler(sManager: SensorManager, s: Sensor) : EventChannel.StreamHandler, SensorEventListener {
+    private val sensorManager: SensorManager = sManager
+    private val accelerometerSensor: Sensor = s
+    private lateinit var eventSink: EventChannel.EventSink
+
+    override fun onListen(arguments: Any?, events: EventChannel.EventSink?) {
+        if (events != null) {
+            eventSink = events
+            sensorManager.registerListener(this, accelerometerSensor, SensorManager.SENSOR_DELAY_UI)
+        }
+    }
+
+    override fun onCancel(arguments: Any?) {
+        sensorManager.unregisterListener(this)
+    }
+
+    override fun onAccuracyChanged(sensor: Sensor?, accuracy: Int) {}
+
+    override fun onSensorChanged(sensorEvent: SensorEvent?) {
+        if (sensorEvent != null) {
+            val axisValues = listOf(sensorEvent.values[0], sensorEvent.values[1], sensorEvent.values[2])
+            eventSink.success(axisValues)
+        }
+    }
+}

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

@@ -1,7 +1,15 @@
+// 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.
+
 package dev.flutter.platform_channels
 
+import android.content.Context
+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.EventChannel
 import io.flutter.plugin.common.MethodChannel
 
 class MainActivity : FlutterActivity() {
@@ -27,5 +35,10 @@ class MainActivity : FlutterActivity() {
                         }
                     }
                 }
+
+        val sensorManger: SensorManager = getSystemService(Context.SENSOR_SERVICE) as SensorManager
+        val accelerometerSensor: Sensor = sensorManger.getDefaultSensor(Sensor.TYPE_ACCELEROMETER)
+        EventChannel(flutterEngine.dartExecutor, "eventChannelDemo")
+                .setStreamHandler(AccelerometerStreamHandler(sensorManger, accelerometerSensor))
     }
 }

platform_channels/lib/main.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/material.dart';
+import 'package:platform_channels/src/event_channel_demo.dart';
 import 'package:platform_channels/src/method_channel_demo.dart';
 
 void main() {
@@ -15,6 +16,7 @@ class PlatformChannelSample extends StatelessWidget {
     return MaterialApp(
       routes: {
         '/methodChannelDemo': (context) => MethodChannelDemo(),
+        '/eventChannelDemo': (context) => EventChannelDemo(),
       },
       title: 'Platform Channel Sample',
       home: HomePage(),
@@ -33,9 +35,13 @@ class DemoInfo {
 
 List<DemoInfo> demoList = [
   DemoInfo(
-    'MethodChannelDemo',
+    'MethodChannel Demo',
     '/methodChannelDemo',
   ),
+  DemoInfo(
+    'EventChannel Demo',
+    '/eventChannelDemo',
+  )
 ];
 
 class HomePage extends StatelessWidget {

platform_channels/lib/src/accelerometer_event_channel.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/services.dart';
+
+/// This class includes the implementation for [EventChannel] to listen to value
+/// changes from the Accelerometer sensor from native side. It has a [readings]
+/// getter to provide a stream of [AccelerometerReadings].
+class Accelerometer {
+  static final _eventChannel = const EventChannel('eventChannelDemo');
+
+  /// Method responsible for providing a stream of [AccelerometerReadings] to listen
+  /// to value changes from the Accelerometer sensor.
+  static Stream<AccelerometerReadings> get readings {
+    return _eventChannel.receiveBroadcastStream().map(
+          (dynamic event) => AccelerometerReadings(
+            event[0] as double,
+            event[1] as double,
+            event[2] as double,
+          ),
+        );
+  }
+}
+
+class AccelerometerReadings {
+  /// Acceleration force along the x-axis.
+  final double x;
+
+  /// Acceleration force along the y-axis.
+  final double y;
+
+  /// Acceleration force along the z-axis.
+  final double z;
+
+  AccelerometerReadings(this.x, this.y, this.z);
+}

platform_channels/lib/src/event_channel_demo.dart

@@ -0,0 +1,58 @@
+// 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/accelerometer_event_channel.dart';
+
+/// Demonstrates how to use [EventChannel] to listen continuous values
+/// of Accelerometer Sensor from platform.
+///
+/// The widget uses a [StreamBuilder] to rebuild it's descendant whenever it
+/// listens a new value from the [Accelerometer.readings] stream. It has three
+/// [Text] widgets to display the value of [AccelerometerReadings.x],
+/// [AccelerometerReadings.y], and [AccelerometerReadings.z] respectively.
+class EventChannelDemo extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    final textStyle = Theme.of(context).textTheme.headline5;
+    return Scaffold(
+      appBar: AppBar(
+        title: Text('EventChannel Demo'),
+      ),
+      body: Center(
+        child: StreamBuilder<AccelerometerReadings>(
+          stream: Accelerometer.readings,
+          builder: (context, snapshot) {
+            if (snapshot.hasError) {
+              return Text(snapshot.error.toString());
+            } else if (snapshot.hasData) {
+              return Column(
+                mainAxisAlignment: MainAxisAlignment.center,
+                children: [
+                  Text(
+                    'x axis: ' + snapshot.data.x.toStringAsFixed(3),
+                    style: textStyle,
+                  ),
+                  Text(
+                    'y axis: ' + snapshot.data.y.toStringAsFixed(3),
+                    style: textStyle,
+                  ),
+                  Text(
+                    'z axis: ' + snapshot.data.z.toStringAsFixed(3),
+                    style: textStyle,
+                  )
+                ],
+              );
+            }
+
+            return Text(
+              'No Data Available',
+              style: textStyle,
+            );
+          },
+        ),
+      ),
+    );
+  }
+}

platform_channels/test/src/event_channel_demo_test.dart

@@ -0,0 +1,73 @@
+// 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/event_channel_demo.dart';
+
+void main() {
+  group('EventChannel Demo tests', () {
+    final sensorValues = [1.3556, 2.3, -0.12];
+    setUpAll(() {
+      // By default EventChannel uses StandardMethodCodec to communicate with
+      // platform.
+      const standardMethod = StandardMethodCodec();
+
+      // This function handles the incoming messages from the platform. It
+      // calls the BinaryMessenger.setMessageHandler registered for the EventChannel
+      // and add the incoming message to the StreamController used by the EventChannel
+      // after decoding the message with codec used by the EventChannel.
+      void emitValues(ByteData event) {
+        ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage(
+          'eventChannelDemo',
+          event,
+          (reply) {},
+        );
+      }
+
+      // Register a mock for EventChannel. EventChannel under the hood uses
+      // MethodChannel to listen and cancel the created stream.
+      ServicesBinding.instance.defaultBinaryMessenger
+          .setMockMessageHandler('eventChannelDemo', (message) async {
+        // Decode the message into MethodCallHandler.
+        final methodCall = standardMethod.decodeMethodCall(message);
+
+        if (methodCall.method == 'listen') {
+          // Emit new sensor values.
+          emitValues(standardMethod.encodeSuccessEnvelope(sensorValues));
+          emitValues(null);
+          return standardMethod.encodeSuccessEnvelope(null);
+        } else if (methodCall.method == 'cancel') {
+          return standardMethod.encodeSuccessEnvelope(null);
+        } else {
+          fail('Expected listen or cancel');
+        }
+      });
+    });
+
+    testWidgets('EventChannel AccelerometerReadings Stream test',
+        (tester) async {
+      await tester.pumpWidget(MaterialApp(
+        home: EventChannelDemo(),
+      ));
+
+      await tester.pumpAndSettle();
+
+      // Check the values of axis. The value is rounded to 3 decimal places.
+      expect(
+        find.text('x axis: ' + sensorValues[0].toStringAsFixed(3)),
+        findsOneWidget,
+      );
+      expect(
+        find.text('y axis: ' + sensorValues[1].toStringAsFixed(3)),
+        findsOneWidget,
+      );
+      expect(
+        find.text('z axis: ' + sensorValues[2].toStringAsFixed(3)),
+        findsOneWidget,
+      );
+    });
+  });
+}