Swift 闭包回调报错： C function pointer cannot be formed from a closure that captures context

最近在写 flutter 跟 ios swift 原生通信的 demo，遇到一个问题，报这个错：

C function pointer cannot be formed from a closure that captures context

代码如下：

 @UIApplicationMain @objc class AppDelegate: FlutterAppDelegate { override func application( _ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? ) -> Bool { GeneratedPluginRegistrant.register(with: self) let controller: FlutterViewCOntroller= window?.rootViewController as! FlutterViewController CFNotificationCenterAddObserver(center, Unmanaged.passUnretained(self).toOpaque(), { (center, observer, name, object, userInfo) in NSLog("Notify received") CustomChannel.sendMessageToFlutter(controller: controller) 

public struct CustomChannel { static func sendMessageToFlutter(controller: FlutterViewController){ let channel = FlutterMethodChannel( name: "paymentview", binaryMessenger: controller.binaryMessenger ) DispatchQueue.main.async { channel.invokeMethod("authorized", arguments: nil) } } } 

swift 现在是边学边写，这个闭包看起来有点看不懂。