Add charging status to Swift version of Platform Channel example (#9436)

examples/platform_channel/platform_channel.iml

@@ -11,5 +11,6 @@
     <orderEntry type="sourceFolder" forTests="false" />
     <orderEntry type="library" name="Dart SDK" level="project" />
     <orderEntry type="library" name="Dart Packages" level="project" />
+    <orderEntry type="library" name="Dart SDK" level="application" />
   </component>
 </module>
\ No newline at end of file

examples/platform_channel_swift/ios/Runner/AppDelegate.swift

@@ -6,7 +6,8 @@ import UIKit
 import Flutter
 
 @UIApplicationMain
-@objc class AppDelegate: FlutterAppDelegate {
+@objc class AppDelegate: FlutterAppDelegate, FlutterStreamHandler {
+  private var eventReceiver: FlutterEventReceiver?;
 
   override func application(
     _ application: UIApplication,
@@ -17,17 +18,20 @@ import Flutter
     batteryChannel.setMethodCallHandler({
       (call: FlutterMethodCall, result: FlutterResultReceiver) -> Void in
       if ("getBatteryLevel" == call.method) {
-          receiveBatteryLevel(result: result);
+        self.receiveBatteryLevel(result: result);
       } else {
         result(FlutterMethodNotImplemented);
       }
       }
     );
+
+    let chargingChannel = FlutterEventChannel.init(name: "samples.flutter.io/charging",
+                                                   binaryMessenger: controller);
+    chargingChannel.setStreamHandler(self);
     return true
   }
-}
 
-private func receiveBatteryLevel(result: FlutterResultReceiver) {
+  private func receiveBatteryLevel(result: FlutterResultReceiver) {
     let device = UIDevice.current;
     device.isBatteryMonitoringEnabled = true;
     if (device.batteryState == UIDeviceBatteryState.unknown) {
@@ -37,4 +41,47 @@ private func receiveBatteryLevel(result: FlutterResultReceiver) {
     } else {
       result(Int(device.batteryLevel * 100));
     }
+  }
+
+  public func onListen(withArguments arguments: Any?,
+                       eventReceiver: @escaping FlutterEventReceiver) -> FlutterError? {
+    self.eventReceiver = eventReceiver;
+    UIDevice.current.isBatteryMonitoringEnabled = true;
+    NotificationCenter.default.addObserver(
+      self,
+      selector: #selector(onBatteryStateDidChange),
+      name: NSNotification.Name.UIDeviceBatteryStateDidChange,
+      object: nil)
+    return nil;
+  }
+
+  @objc private func onBatteryStateDidChange(notification: NSNotification) {
+    if (eventReceiver == nil) {
+      return;
+    }
+
+    let state = UIDevice.current.batteryState;
+    switch state {
+    case UIDeviceBatteryState.full:
+      eventReceiver!("charging");
+      break;
+    case UIDeviceBatteryState.charging:
+      eventReceiver!("charging");
+      break;
+    case UIDeviceBatteryState.unplugged:
+      eventReceiver!("discharging");
+      break;
+    default:
+      eventReceiver!(FlutterError.init(code: "UNAVAILABLE",
+                                       message: "Charging status unavailable",
+                                       details: nil));
+      break;
+    }
+  }
+
+  public func onCancel(withArguments arguments: Any?) -> FlutterError? {
+    NotificationCenter.default.removeObserver(self);
+    eventReceiver = nil;
+    return nil;
+  }
 }

examples/platform_channel_swift/lib/main.dart

@@ -13,36 +13,67 @@ class PlatformChannel extends StatefulWidget {
 }
 
 class _PlatformChannelState extends State<PlatformChannel> {
-  static const PlatformMethodChannel platform = const PlatformMethodChannel('samples.flutter.io/battery');
-  String _batteryLevel = '';
+  static const PlatformMethodChannel methodChannel =
+      const PlatformMethodChannel('samples.flutter.io/battery');
+  static const PlatformEventChannel eventChannel =
+      const PlatformEventChannel('samples.flutter.io/charging');
+
+  String _batteryLevel = 'Battery level: unknown.';
+  String _chargingStatus = 'Battery status: unknown.';
 
   Future<Null> _getBatteryLevel() async {
     String batteryLevel;
     try {
-      final int result = await platform.invokeMethod('getBatteryLevel');
-      batteryLevel = 'Battery level at $result % .';
-    } on PlatformException catch (e) {
-      batteryLevel = "Failed to get battery level: '${e.message}'.";
+      final int result = await methodChannel.invokeMethod('getBatteryLevel');
+      batteryLevel = 'Battery level: $result%.';
+    } on PlatformException {
+      batteryLevel = "Failed to get battery level.";
     }
     setState(() {
       _batteryLevel = batteryLevel;
     });
   }
 
+  @override
+  void initState() {
+    super.initState();
+    eventChannel.receiveBroadcastStream().listen(_onEvent, onError: _onError);
+  }
+
+  void _onEvent(String event) {
+    setState(() {
+      _chargingStatus =
+          "Battery status: ${event == 'charging' ? '' : 'dis'}charging.";
+    });
+  }
+
+  void _onError(PlatformException error) {
+    setState(() {
+      _chargingStatus = "Battery status: unknown.";
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return new Material(
-      child: new Center(
       child: new Column(
         mainAxisAlignment: MainAxisAlignment.spaceEvenly,
         children: <Widget>[
-            new RaisedButton(
-              child: const Text('Get Battery Level'),
+          new Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              new Text(_batteryLevel, key: const Key('Battery level label')),
+              new Padding(
+                padding: const EdgeInsets.all(16.0),
+                child: new RaisedButton(
+                  child: const Text('Refresh'),
                   onPressed: _getBatteryLevel,
                 ),
-            new Text(_batteryLevel, key: const Key('Battery level label')),
+              ),
             ],
           ),
+          new Text(_chargingStatus),
+        ],
       ),
     );
   }

examples/platform_channel_swift/platform_channel_swift.iml

@@ -10,6 +10,7 @@
     </content>
     <orderEntry type="sourceFolder" forTests="false" />
     <orderEntry type="library" name="Dart SDK" level="project" />
+    <orderEntry type="library" name="Dart SDK" level="application" />
     <orderEntry type="library" name="Dart Packages" level="project" />
   </component>
 </module>
\ No newline at end of file