Flutter与Native交换主要是使用PlatformChannel功能

PlatformChannel

Platformchannle分为三种类型

• BasicMessageChannel
• MethodChannel
• EventChannel

BasicMessageChannel

用于传递数据。Flutter与原生项目的资源是不共享的，可以通过BasicMessageChannel 来获取Native项目的图标等资源

MethodChannel

传递方法调用。Flutter主动调用Native的方法，并获取相应的返回值。比如获取系统电量，发起Toast等系统API，可以通过这个完成。

EventChannel

传递事件。Native将时间通知到Flutter。比如Flutter需要监听网络情况。EventChannel可以将Flutter的一个监听器交给Native，Native去做网络广播的监听，当收到广播之后借助 EventChannel调用Flutter注册的监听，完成对Flutter的事件通知。

具体实现

BasicMessageChannel

• Flutter

  static const messageChannel = const BasicMessageChannel('samples.flutter.io/message', StandardMessageCodec());
  
  static const messageChannel2 = const BasicMessageChannel('smaples.flutter.io/message2', StandardMessageCodec());
  
  Future<String> sendMessage() async {
      String reply = await messageChannel.send('发送给Native的数据');
      print('reply: $reply');
      return reply;
  }
  
  void receiveMessage() {
      messageChannel2.setMessageHandler((message) async {
         print('message : $message');
          return '从Native端返回来的数据'；
      });
  }
  
  @Override
  void initState() {
      super.initState();
      receiveMessage();
      sendMessage();
  }
  

• iOS 先不动

• Android

  BasicMessageChanngl messageChannel = new BasicMessageChannel<Object>(getFlutterView(), "samples.flutter.io/message2", StandardMessageCodes.INSTANCE);
  
  // 接收来自Flutter的消息
  messageChannel.setMessageHandler(new BasicMessageChannel.MessageHandler<Object>() {
      @Override
      public void onMessage(object o, BasicMessageChannel.Reply<Object> reply) {
          Log.d("jimbray", "OnMessage" + o);
          reply.reply("返回给Flutter的数据");
      }
  });
  
  // 发送数据给Flutter
  BasicMessageChannel messageChannel2 = new BasicMessageChannel<Object>(
  getFlutterView(), "samples.flutter.io/message2", StandardMessageCodec.INSTANCE);
  
  // 发送消息到Flutter
  messageChannel2.send("发送到Flutter的消息", new BasicMessageChannel.Reply<Object>() {
     @Override
      public void reply(Object o) {
          Log.d("jimbray", "onReply: " + o);
      }
  });
  

MethodChannel

• Flutter

  static const platform = const MethodChannel('samples.flutter.io/battery');
  
  Future<Null> _getBatteryLevel() async {
      String batteryLevel;
      try {
        final int result = awai platform.invokeMethod('getBatteryLevel');
        batteryLevel = 'BatteryLevel at $result %';
      } on PlatformException catch(e) {
          batterylevel = 'Failed to get battery levet: "${e.message}".';
      }
      
      setState(（） {
          _batteryLevel = batterLevel;
      })；
  }
  

• iOS先不动

• Android

  new MethodChannel(getFlutterView(), "samples.flutter.io/battery").setMethodCallHandler(new MethodCallHandler() {
      @Override
      public void onMethodCall(MethodCall call, Result result) {
          if (call.method.equals("getBatteryLevel")) {
              int batteryLevel = _getBatteryLevel();
              
              if (batteryLevel != -1) {
                  result.success(batteryLevel);
              } else {
                  result.error("UNAVAILABLE", "Battery level is not available.", null);
              }
          } else {
              result.notImplemented();
          }
      }
  });
  
  private int getBatterylevel() {
      // 实现Android平台的 getBatteryLevel 代码即可
  }
  

EventChannel

• Flutter

  static const EventChannel _eventChannel = const EventChannel('samples.flutter.io/test');
  
  void _onEvent(Object event) {
      print('从Native发送过来的消息内容: $event');
  }
  
  void _onError(Object error) {
      print('从Native发送过来的错误')；
  }
  
  @Override
  void initState() {
      super.initState();
      _eventChannel.receiveBroadcastStream().listen(_onEvent, onError: _onError);
  }
  

• iOS先不动

• Android

  new EventChannel(getFlutterView(), "samples.flutter.io/test").setStreanHandler(
  new EventChannel.StreamHandler() {
      @Override
      public void onListen(Object o, EventChannel.EventSink eventSink) {
          this.eventSink = eventSink;
      }
      
      @Override
      public void onCancel(Object o) {
          
      }
      
      
  });
  
  private EventChannel.EventSink eventSink;
  private int count = 0;
  
  private Handler handler = new Handler() {
      @Override
      public void handleMessage(Message msg) {
          super.handleMessage();
          eventSink.success((count++) + "主动发送消息到Flutter")；
      }
  }