Flutter开发进阶之Package

通常我们在Flutter开发中需要将部分功能与整体项目隔离，一般有两种方案Plugin和Package，Application是作为主体项目，Module是作为原生项目接入Flutter模块。
Flutter开发进阶
当独立模块不需要与原生项目通讯只需要Plugin就可以，但是当需要与原生通讯就需要Package。

一、创建Package

cd /Users/kevin/Desktop/My

flutter create --org com.kevin --template=plugin --platforms=android,ios -a kotlin -i swift  package_demo

创建Package必须指定平台：
android、ios、web、linux、macos 和 windows。
命令中-a后是指定Android的开发语言，-i是指定iOS的开发语言。
Package

二、通讯

Package会自动创建MethodChannel，还可以根据需要创建BasicMessageChannel和EventChannel。

Flutter

class MethodChannelPackageDemo extends PackageDemoPlatform {
  /// The method channel used to interact with the native platform.
  @visibleForTesting
  final methodChannel = const MethodChannel('package_demo_method');
  final messageChannel = const BasicMessageChannel('package_demo_message', 
      StandardMessageCodec());
  final eventChannel = const EventChannel('package_demo_event');

  MethodChannelPackageDemo() {
    methodChannel.setMethodCallHandler((call) async {
      /// 方法
      return call.method;
    });
    messageChannel.setMessageHandler((message) async {
      /// 字符串和半结构化
      return message;
    });
    eventChannel.receiveBroadcastStream().listen((event) {
      /// 事件流
    }, onError: (error) {
      ///
    }, cancelOnError: true,);

  }
  
  @override
  Future<String?> getPlatformVersion() async {
    final version = await methodChannel.invokeMethod<String>('getPlatformVersion');
    return version;
  }
}

iOS

public class PackageDemoPlugin: NSObject, FlutterPlugin {
  public static func register(with registrar: FlutterPluginRegistrar) {
    let methodChannel = FlutterMethodChannel(name: "package_demo_method", binaryMessenger: registrar
    .messenger())
    let instance = PackageDemoPlugin()
    registrar.addMethodCallDelegate(instance, channel: methodChannel)
  }

  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
    switch call.method {
    case "getPlatformVersion":
      result("iOS " + UIDevice.current.systemVersion)
    default:
      result(FlutterMethodNotImplemented)
    }
  }
}

Android

class PackageDemoPlugin: FlutterPlugin, MethodCallHandler {
  /// The MethodChannel that will the communication between Flutter and native Android
  ///
  /// This local reference serves to register the plugin with the Flutter Engine and unregister it
  /// when the Flutter Engine is detached from the Activity
  private lateinit var methodChannel : MethodChannel

  override fun onAttachedToEngine(flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
    methodChannel = MethodChannel(flutterPluginBinding.binaryMessenger, "package_demo_method")
    methodChannel.setMethodCallHandler(this)
  }

  override fun onMethodCall(call: MethodCall, result: Result) {
    if (call.method == "getPlatformVersion") {
      result.success("Android ${android.os.Build.VERSION.RELEASE}")
    } else {
      result.notImplemented()
    }
  }

  override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {
    channel.setMethodCallHandler(null)
  }
}

三、调用原生控件

Flutter

class PackageView extends StatelessWidget {
  const PackageView({super.key});

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    if (Platform.isAndroid) {
      return AndroidView(
        viewType: 'package_demo/android',
        onPlatformViewCreated: (id) {},
        creationParams: const {'type': 'android'},
        creationParamsCodec: const StandardMessageCodec(),
      );
    } else if (Platform.isIOS) {
      return UiKitView(
        viewType: 'package_demo/ios',
        onPlatformViewCreated: (id) {},
        creationParams: const {'type': 'ios'},
        creationParamsCodec: const StandardMessageCodec(),
      );
    }
    return const SizedBox();
  }
}

iOS

public class PackageDemoPlugin: NSObject, FlutterPlugin {
  public static func register(with registrar: FlutterPluginRegistrar) {
    let methodChannel = FlutterMethodChannel(name: "package_demo_method", binaryMessenger: registrar
    .messenger())
    let instance = PackageDemoPlugin()
    registrar.addMethodCallDelegate(instance, channel: methodChannel)
    registrar.register(PackageViewFactory(), withId: "package_demo/ios")
  }

  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
    switch call.method {
    case "getPlatformVersion":
      result("iOS " + UIDevice.current.systemVersion)
    default:
      result(FlutterMethodNotImplemented)
    }
  }
}

class PackageViewFactory: NSObject, FlutterPlatformViewFactory {
    
    func create(withFrame frame: CGRect, viewIdentifier viewId: Int64, arguments args: Any?) -> FlutterPlatformView {
        return PackageView()
    }
    
    func createArgsCodec() -> FlutterMessageCodec & NSObjectProtocol {
        return FlutterStandardMessageCodec.sharedInstance()
    }
    
}

class PackageView: NSObject, FlutterPlatformView {
    
    func view() -> UIView {
        return UIView()
    }
    
}

Android

class PackageDemoPlugin: FlutterPlugin, MethodCallHandler {
  /// The MethodChannel that will the communication between Flutter and native Android
  ///
  /// This local reference serves to register the plugin with the Flutter Engine and unregister it
  /// when the Flutter Engine is detached from the Activity
  private lateinit var methodChannel : MethodChannel

  override fun onAttachedToEngine(flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
    methodChannel = MethodChannel(flutterPluginBinding.binaryMessenger, "package_demo_method")
    methodChannel.setMethodCallHandler(this)
    flutterPluginBinding.platformViewRegistry.registerViewFactory("package_demo/android", PackageViewFactory());
  }

  override fun onMethodCall(call: MethodCall, result: Result) {
    if (call.method == "getPlatformVersion") {
      result.success("Android ${android.os.Build.VERSION.RELEASE}")
    } else {
      result.notImplemented()
    }
  }

  override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {
    methodChannel.setMethodCallHandler(null)
  }
}

class PackageViewFactory: PlatformViewFactory(StandardMessageCodec.INSTANCE){

    override fun create(context: Context?, viewId: Int, args: Any?): PlatformView {
        return PackageView(context)
    }

}

class PackageView internal constructor(context: Context?): PlatformView{

    override fun getView(): View? {
        TODO("Not yet implemented")
    }

    override fun dispose() {
        TODO("Not yet implemented")
    }

}