蹭个热门：Flutter Plugin数据传递通信实例梳理

今天突然翻到放置大概4个月的Flutter笔记--Flutter Plugin数据传递通信实例梳理

插件与Native通信

1. Flutter向native发送通信(分析实例： SharedPreferences)

Flutter通过Dart与Native发送数据通信请求是通过MethodChannel 调用invokeMethod 来实现

const MethodChannel _kChannel = const MethodChannel('plugins.flutter.io/shared_preferences');

使用Dart语言调用,获取数据

获取preferences数据：

final Map<Object, Object> fromSystem = await _kChannel.invokeMethod('getAll');

通过Dart向Native发送数据，并获得返回结果

Future<bool> _setValue(String valueType, String key, Object value) { final Map<String, dynamic> params = <String, dynamic>{ 'key': '$_prefix$key', }; if (value == null) { _preferenceCache.remove(key); return _kChannel .invokeMethod('remove', params) .then<bool>((dynamic result) => result); } else { _preferenceCache[key] = value; params['value'] = value; return _kChannel .invokeMethod('set$valueType', params) .then<bool>((dynamic result) => result); } }

数据通信在Flutter中定义是Plugin，因此iOS需要遵循Plugin协议``` FlutterPlugin ``` Android实现```MethodCallHandler```

，通信过程中是根据Dart中设置的ChannelName来区分对应的Plugin

对于跨平台来说流程是统一的，我们通过iOS来说通信流程，然后在此基础上稍微梳理一下Android的流程

通信基本流程

1. 注册Plugin

2. Channel与messager进行匹配

3. 通信

iOS：

声明出一个Plugin

#import <Flutter/Flutter.h> @interface FLTSharedPreferencesPlugin : NSObject<FlutterPlugin> @end

1. 注册

对于每一个遵循```FlutterPlugin```的类都会在系统创建plugin时实现注册方法```+ (void)registerWithRegistrar:(NSObject<FlutterPluginRegistrar> *)registrar```

2. 匹配

在系统的注册方法中需要将通信的Channel与regster所携带来的messager进行匹配绑定

FlutterMethodChannel *channel = [FlutterMethodChannel methodChannelWithName:CHANNEL_NAME binaryMessenger:registrar.messenger];

3. 通信

通信是相互的，flutter向native发送数据通信之后，native需要通过回调向flutter做出反馈

Channel通过handler来处理平台之间的数据沟通 [channel setMethodCallHandler:^(FlutterMethodCall *call, FlutterResult result) {} 拿 getAll 作说明： NSString *method = [call method]; NSDictionary *arguments = [call arguments]; if ([method isEqualToString:@"getAll"]) { result(getAllPrefs()); } 1. 对于通信方法的区分是采用字符串匹配的方式来达到平台的兼容 2. arguments中携带的是flutter传递给native的数据 3. 采用回调的当时进行数据结果的反馈

下面是iOS具体的通信过程

[channel setMethodCallHandler:^(FlutterMethodCall *call, FlutterResult result) { NSString *method = [call method]; NSDictionary *arguments = [call arguments]; if ([method isEqualToString:@"getAll"]) { result(getAllPrefs()); } else if ([method isEqualToString:@"setBool"]) { NSString *key = arguments[@"key"]; NSNumber *value = arguments[@"value"]; [[NSUserDefaults standardUserDefaults] setBool:value.boolValue forKey:key]; result(@YES); } else if ([method isEqualToString:@"setInt"]) { NSString *key = arguments[@"key"]; NSNumber *value = arguments[@"value"]; // int type in Dart can come to native side in a variety of forms // It is best to store it as is and send it back when needed. // Platform channel will handle the conversion. [[NSUserDefaults standardUserDefaults] setValue:value forKey:key]; result(@YES); } else if ([method isEqualToString:@"setDouble"]) { NSString *key = arguments[@"key"]; NSNumber *value = arguments[@"value"]; [[NSUserDefaults standardUserDefaults] setDouble:value.doubleValue forKey:key]; result(@YES); } else if ([method isEqualToString:@"setString"]) { NSString *key = arguments[@"key"]; NSString *value = arguments[@"value"]; [[NSUserDefaults standardUserDefaults] setValue:value forKey:key]; result(@YES); } else if ([method isEqualToString:@"setStringList"]) { NSString *key = arguments[@"key"]; NSArray *value = arguments[@"value"]; [[NSUserDefaults standardUserDefaults] setValue:value forKey:key]; result(@YES); } else if ([method isEqualToString:@"commit"]) { // synchronize is deprecated. // "this method is unnecessary and shouldn't be used." result(@YES); } else if ([method isEqualToString:@"remove"]) { [[NSUserDefaults standardUserDefaults] removeObjectForKey:arguments[@"key"]]; result(@YES); } else if ([method isEqualToString:@"clear"]) { NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; for (NSString *key in getAllPrefs()) { [defaults removeObjectForKey:key]; } result(@YES); } else { result(FlutterMethodNotImplemented); } }];

Android待后续梳理