Flutter与android原生通信

Flutter 与 Android/iOS 之间信息交互通过 Platform Channel 进行桥接； Flutter 定义了三种不同的 Channel；但无论是传递方法还是传递事件，其本质上都是数据的传递；

1. MethodChannel：用于传递方法调用；
2.  EventChannel：用于数据流信息通信;
3. BasicMessageChannel：用于传递字符串和半结构化的信息；

每种 Channel 均包含三个成员变量；

1. name：代表 Channe 唯一标识符，Channel 可以包含多个，但 name 为唯一的；
2. messager：代表消息发送与接收的工具 BinaryMessenger；
3. codec：代表消息的编解码器

1、MethodChannel:

flutter代码：

// 调用原生方法
static const methodChannel = const MethodChannel('flutter_and_native_101');

static Future<dynamic> invokNative(String method, {Map arguments}) async {
  if (arguments == null) {
    return await methodChannel.invokeMethod(method);
  } else {
    return await methodChannel.invokeMethod(method, arguments);
  }
}

// 监听原生返回
Future<dynamic> nativeMessageListener() async {
    methodChannel.setMethodCallHandler((resultCall) {
      MethodCall call = resultCall;
      String method = call.method;
      Map arguments = call.arguments;

      int code = arguments["code"];
      String message = arguments["message"];
      setState(() {
        recive += " code $code message $message and method $method \n";
        print(recive);
      });
      return null;
    });
  }

// 调用
onPressed: () {
    invokNative("test")
    ..then((result) {
        int code = result["code"];
        String message = result["message"];
        setState(() {
        	recive = "invokNative 中的回调 code $code message $message ";
        });
    });
}

android代码：

private void methodChannelFunction() {
    mMethodChannel = new MethodChannel(getFlutterView(), "flutter_and_native_101");
    //设置监听
    mMethodChannel.setMethodCallHandler(
            new MethodChannel.MethodCallHandler() {
                @Override
                public void onMethodCall(MethodCall call, MethodChannel.Result result) {
                    String lMethod = call.method;

                    if (lMethod.equals("test")) {
                        Toast.makeText(mContext, "flutter 调用到了 android test", Toast.LENGTH_SHORT).show();
                        Map<String, Object> resultMap = new HashMap<>();
                        resultMap.put("message", "result.success 返回给flutter的数据");
                        resultMap.put("code", 300);
                        result.success(resultMap);

                    } else if (lMethod.equals("test2")) {
                        //Toast.makeText(mContext, "flutter 调用到了 android test", Toast.LENGTH_SHORT).show();
                        Map<String, Object> resultMap = new HashMap<>();
                        resultMap.put("message", "android 主动调用 flutter test 方法");
                        resultMap.put("code", 301);
                        mMethodChannel.invokeMethod("test", resultMap);

                        mHandler.postDelayed(new Runnable() {
                            @Override
                            public void run() {
                                Map<String, Object> resultMap2 = new HashMap<>();
                                resultMap2.put("message", "android 主动调用 flutter test 方法 delay 2000ms");
                                resultMap2.put("code", 302);
                                mMethodChannel.invokeMethod("test2", resultMap2);
                            }
                        }, 2000);
                    } else if (lMethod.equals("test3")) {
                        //测试通过Flutter打开Android Activity
                        Toast.makeText(mContext, "flutter 调用到了 android test3", Toast.LENGTH_SHORT).show();
                        Intent lIntent = new Intent(MainActivity.this, TestMethodChannelActivity.class);
                        MainActivity.this.startActivity(lIntent);
                    } else {
                        result.notImplemented();
                    }
                }
            }
    );
}

通过 flutter_and_native_101 唯一标识将flutter和andorid之间的 channel 连接起来。flutter 传递对应的方法名称在native 接受方法后解析名称，在对比调用不同逻辑。

2、EventChannel:相当于接收来自native的通知

只能是原生发送消息给Flutter端，例如监听手机电量变化，网络变化，传感器等。

flutter 端：

//EventChannel（ 用于数据流（event streams）的通信）
static const EventChannel _eventChannel = const EventChannel('flutter_and_native_102');

Future<dynamic> nativeMessageListener() async {
  _eventChannel.receiveBroadcastStream().listen((arguments) {
    int code = arguments["code"];
    String message = arguments["message"];
    setState(() {
      recive +=
          " code $code message $message \n";
      print(recive);
    });
  }, onError: (event) {
    print(event);
  });
}

android原生：

/**
 * 此方法适用于android 系统有通知通知到flutter的场景
 *
 * */
private void eventChannelFunction() {
    EventChannel lEventChannel = new EventChannel(getFlutterView(), "flutter_and_native_102");
    lEventChannel.setStreamHandler(
            new EventChannel.StreamHandler() {
                @Override
                public void onListen(Object o, EventChannel.EventSink eventSink) {
                    mEventSink = eventSink;
                    Log.d("zxzx","event sink = " + o);
                    mHandler.post(new Runnable() {
                        @Override
                        public void run() {
                            Map<String, Object> resultMap = new HashMap<>();
                            resultMap.put("message", "注册成功");
                            resultMap.put("code", 400);
                            eventSink.success(resultMap);
                        }
                    });
                }

                @Override
                public void onCancel(Object o) {

                }
            }
    );
}

同理，flutter注册监听，监听 flutter_and_native_102 channel来的广播。

3、BasicMessageChannel ：

它是可以双端通信的，flutter端可以给Android发送消息，Android也可以给Flutter发送消息。

flutter 端：

static const messageChannel = const BasicMessageChannel( 'flutter_and_native_100', StandardMessageCodec());

  //发送消息
  Future<Map> sendMessage(Map json) async {
    Map reply = await messageChannel.send(json);

    //解析 原生发给 Flutter 的参数
    int code = reply["code"];
    String message = reply["message"];

    setState(() {
      recive = "code:$code message:$message";
    });
    return reply;
  }

  //接收消息监听
  void receiveMessage() {
    messageChannel.setMessageHandler((result) async {
      //解析 原生发给 Flutter 的参数
      int code = result["code"];
      String message = result["message"];

      setState(() {
        recive = "receiveMessage: code:$code message:$message";
      });
      return 'Flutter 已收到消息';
    });
  }

android端：

private void messageChannelFunction() {
        //消息接收监听
        //BasicMessageChannel （主要是传递字符串和一些半结构体的数据）
        mMessageChannel = new BasicMessageChannel<Object>(getFlutterView(), "flutter_and_native_100", StandardMessageCodec.INSTANCE);
        // 接收消息监听
        mMessageChannel.setMessageHandler(new BasicMessageChannel.MessageHandler<Object>() {
            @Override
            public void onMessage(Object o, BasicMessageChannel.Reply<Object> reply) {

                System.out.println("onMessage: " + o.toString());
                Map lJSONObject = null;
                //解析Flutter 传递的参数
                lJSONObject = (HashMap) o;
                //方法名标识
                Object lMethod = lJSONObject.get("method");
                Log.d("MainActivity","lmethod = " + lMethod);
                //测试 reply.reply()方法 发消息给Flutter
                if (lMethod.equals("test")) {
                    Toast.makeText(mContext, "flutter 调用到了 android test", Toast.LENGTH_SHORT).show();
                    Map<String, Object> resultMap = new HashMap<>();
                    resultMap.put("message", "reply.reply 返回给flutter的数据");
                    resultMap.put("code", 200);
                    reply.reply(resultMap);
                } else if (lMethod.equals("test2")) {
                    //测试 mMessageChannel.send 发消息给Flutter
                    channelSendMessage();
                } else if (lMethod.equals("test3")) {
                    //测试通过Flutter打开Android Activity
                    Toast.makeText(mContext, "flutter 调用到了 android test3", Toast.LENGTH_SHORT).show();
                    Intent lIntent = new Intent(MainActivity.this, TestBasicMessageActivity.class);
                    MainActivity.this.startActivity(lIntent);
                }
            }
        });
    }

    private void channelSendMessage() {
        Toast.makeText(mContext, "flutter 调用到了 android test", Toast.LENGTH_SHORT).show();
        Map<String, Object> resultMap = new HashMap<>();
        resultMap.put("message", "message Channel.reply 返回给flutter的数据");
        resultMap.put("code", 201);

        mMessageChannel.send(resultMap, new BasicMessageChannel.Reply<Object>() {
            @Override
            public void reply(Object o) {
                Log.d("MainActivity", "mMessageChannel send 回调 " + o);
            }
        });
    }

具体的使用哪种通信方式，看具体的使用场景。