flutter与Native交互是必不可少的，今天梳理一下，flutter监听native消息

大致流程

1. flutter注册EventChannel
2. flutter EventChannel监听native消息
3. native通过EventChannel发送消息

代码梳理

1 flutter Event监听

const EventChannel("App/Event/Channel", const StandardMethodCodec());

//开始监听
@override
  void initState() {
    // TODO: implement initState
    super.initState();
    _eventChannel
        .receiveBroadcastStream("init")
        .listen(_onEvent, onError: _onError);
  }

// 数据接收
  void _onEvent(Object value) {
    print(value);
}
// 错误处理
  void _onError(dynamic) {}

说明：对于receiveBroadcastStream建议添加名称作为native中传递数据的参数使用
2 native 通过Event广播数据
2.1 初始化

FlutterEventChannel *eventChannel = [FlutterEventChannel eventChannelWithName:@"App/Event/Channel" binaryMessenger:flutterViewController];

    [eventChannel setStreamHandler:self];

2.2 数据代理 FlutterStreamHandler

- (FlutterError* _Nullable)onListenWithArguments:(id _Nullable)arguments
                                       eventSink:(FlutterEventSink)events {}//此处的arguments可以转化为刚才receiveBroadcastStream("init")的名称，这样我们就可以一个event来监听多个方法实例
- (FlutterError* _Nullable)onCancelWithArguments:(id _Nullable)arguments {}

传递数据实例：

#pragma mark - <FlutterStreamHandler>
// // 这个onListen是Flutter端开始监听这个channel时的回调，第二个参数 EventSink是用来传数据的载体。
- (FlutterError* _Nullable)onListenWithArguments:(id _Nullable)arguments
                                       eventSink:(FlutterEventSink)events {
    
    // arguments flutter给native的参数
    // 回调给flutter， 建议使用实例指向，因为该block可以使用多次
    if (events) {
        NSMutableDictionary * params = [NSMutableDictionary dictionaryWithCapacity:0];
        [params setValue:mReferNo forKey:@"ataNo"];
        [params setValue:mDocType forKey:@"docType"];
        [params setValue:self.aircraftNo forKey:@"aircraftNo"];
//        [params setValue:[[NetworkingTools networkHeaders]   modelToJSONString] forKey:@"headers"];
//        [params setValue:[NetworkingTools networkHeaders] forKey:@"headers"];
        [params setValue:@"我是标题" forKey:@"title"];
        [params addEntriesFromDictionary:[NetworkingTools networkHeaders] ];
        events([params modelToJSONString]);
    }
    return nil;
}

/// flutter不再接收
- (FlutterError* _Nullable)onCancelWithArguments:(id _Nullable)arguments {
    // arguments flutter给native的参数
    return nil;
}

最后是native端调用

  FlutterViewController * flutterViewController = [[FlutterViewController alloc] init];
    [flutterViewController setInitialRoute:@"App"];
    
    flutterViewController.view.backgroundColor = [UIColor whiteColor];
    FlutterEventChannel *eventChannel = [FlutterEventChannel eventChannelWithName:@"App/Event/Channel" binaryMessenger:flutterViewController];
 
    [eventChannel setStreamHandler:self];

通过以上梳理我们基本就可以进行native反向主动给flutter发送数据

问题踩坑

native发送数据是NSDictionry不要进行内部嵌套：@{@"key":@{}}这样是不通过的

channel命名建议

1. Android采用 packagename + eventType + channelname
2. iOS 采用 bundleidentifier + event type + channelname