Flutter 即学即用系列博客——09 EventChannel 实现原生与 Flutter 通信（一）

String _chargingStatus = 'Battery status: unknown.';Text(_chargingStatus),

static const EventChannel eventChannel = EventChannel('samples.flutter.io/charging');

  @override  void initState() {    super.initState();    eventChannel.receiveBroadcastStream().listen(_onEvent, onError: _onError);  }
  void _onEvent(Object event) {    setState(() {      _chargingStatus =      "Battery status: ${event == 'charging' ? '' : 'dis'}charging.";    });  }
  void _onError(Object error) {    setState(() {        PlatformException exception = error;        _chargingStatus = exception?.message ?? 'Battery status: unknown.';    });  }

PlatformException exception = error;

private static final String CHARGING_CHANNEL = "samples.flutter.io/charging";

new EventChannel((FlutterView) flutterView, CHARGING_CHANNEL).setStreamHandler(        new EventChannel.StreamHandler() {
            @Override            public void onListen(Object arguments, EventChannel.EventSink events) {            }
            @Override            public void onCancel(Object arguments) {            }        });

new EventChannel((FlutterView)flutterView, CHARGING_CHANNEL).setStreamHandler(        new EventChannel.StreamHandler() {            private BroadcastReceiver chargingStateChangeReceiver;            @Override            public void onListen(Object arguments, EventChannel.EventSink events) {                chargingStateChangeReceiver = createChargingStateChangeReceiver(events);                registerReceiver(                        chargingStateChangeReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));            }
            @Override            public void onCancel(Object arguments) {                unregisterReceiver(chargingStateChangeReceiver);                chargingStateChangeReceiver = null;            }        });
private BroadcastReceiver createChargingStateChangeReceiver(final EventChannel.EventSink events) {    return new BroadcastReceiver() {        @Override        public void onReceive(Context context, Intent intent) {            int status = intent.getIntExtra(BatteryManager.EXTRA_STATUS, -1);
            if (status == BatteryManager.BATTERY_STATUS_UNKNOWN) {                events.error("UNAVAILABLE", "Charging status unavailable", null);            } else {                boolean isCharging = status == BatteryManager.BATTERY_STATUS_CHARGING ||                        status == BatteryManager.BATTERY_STATUS_FULL;                events.success(isCharging ? "charging" : "discharging");            }        }    };}

PlatformException({  @required this.code,  this.message,  this.details,}) : assert(code != null);

Stream<dynamic> receiveBroadcastStream([dynamic arguments]) {    final MethodChannel methodChannel = MethodChannel(name, codec);    StreamController<dynamic> controller;    controller = StreamController<dynamic>.broadcast(onListen: () async {      BinaryMessages.setMessageHandler(name, (ByteData reply) async {        if (reply == null) {          controller.close();        } else {          try {            controller.add(codec.decodeEnvelope(reply));          } on PlatformException catch (e) {            controller.addError(e);          }        }        return null;      });      try {        await methodChannel.invokeMethod('listen', arguments);      } catch (exception, stack) {        FlutterError.reportError(FlutterErrorDetails(          exception: exception,          stack: stack,          library: 'services library',          context: 'while activating platform stream on channel $name',        ));      }    }, onCancel: () async {      BinaryMessages.setMessageHandler(name, null);      try {        await methodChannel.invokeMethod('cancel', arguments);      } catch (exception, stack) {        FlutterError.reportError(FlutterErrorDetails(          exception: exception,          stack: stack,          library: 'services library',          context: 'while de-activating platform stream on channel $name',        ));      }    });    return controller.stream;  }