swift – The right way to use occasion methodology as callback for operate which takes solely func or literal closure in ios flutter

I’m engaged on the flutter_downloader iOS configuration and I’ve no data of swift. I get an error however I do not know methods to clear up it. Please recommend how can I format my code so it begins working correctly. Under is my code of AppDelegate.swift:

 import UIKit
import Flutter
import FirebaseCore
import Firebase
import flutter_downloader

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate, MessagingDelegate {
  override func utility(
    _ utility: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    FirebaseApp.configure()
    GeneratedPluginRegistrant.register(with: self)
     FlutterDownloaderPlugin.setPluginRegistrantCallback(registerPlugins)
     Messaging.messaging().delegate = self
        if #out there(iOS 10.0, *) {
            // For iOS 10 show notification (despatched through APNS)
  UNUserNotificationCenter.present().delegate = self as? UNUserNotificationCenterDelegate
            let authOptions: UNAuthorizationOptions = [.alert, .badge, .sound]
            UNUserNotificationCenter.present().requestAuthorization(
                    choices: authOptions,
                    completionHandler: {_, _ in })
        }
        utility.registerForRemoteNotifications()
    return tremendous.utility(utility, didFinishLaunchingWithOptions: launchOptions)
  }

  non-public func registerPlugins(registry: FlutterPluginRegistry) {
    if (!registry.hasPlugin("FlutterDownloaderPlugin")) {
       FlutterDownloaderPlugin.register(with: registry.registrar(forPlugin: "FlutterDownloaderPlugin")!)
    }
}}