freshchat库重载了原生ios函数（userNotificationCenter），我们只是添加了对父构造函数的调用
超级用户通知中心（中心，将呈现：将显示，带有完成处理程序：使用完成处理程序）
下面的代码（AppDelegate.swift）

import Flutter
import Firebase
import UserNotifications

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    FirebaseApp.configure()
    GeneratedPluginRegistrant.register(with: self)

    let viewController = UIApplication.shared.windows.first!.rootViewController as! UIViewController
    window = FreshchatSdkPluginWindow(frame: UIScreen.main.bounds)
    window.rootViewController = viewController

    UNUserNotificationCenter.current().delegate = self    
    UNUserNotificationCenter.current().requestAuthorization(options:[.badge, .alert, .sound]){ (granted, error) in }
    UIApplication.shared.registerForRemoteNotifications()

    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }

  override func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
    FreshchatSdkPlugin().setPushRegistrationToken(deviceToken)
  }

  //@available(iOS 10.0, *)
  override func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent: UNNotification, withCompletionHandler: @escaping (UNNotificationPresentationOptions)->()) {
    let freshchatSdkPlugin = FreshchatSdkPlugin()
    if freshchatSdkPlugin.isFreshchatNotification(willPresent.request.content.userInfo) {
      freshchatSdkPlugin.handlePushNotification(willPresent.request.content.userInfo)
    } else {
      super.userNotificationCenter(center, willPresent: willPresent, withCompletionHandler: withCompletionHandler)
    }
  }

  //@available(iOS 10.0, *)
  override func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive: UNNotificationResponse, withCompletionHandler: @escaping ()->()) {
    let freshchatSdkPlugin = FreshchatSdkPlugin()
    if freshchatSdkPlugin.isFreshchatNotification(didReceive.notification.request.content.userInfo) {
      freshchatSdkPlugin.handlePushNotification(didReceive.notification.request.content.userInfo) //Handled for freshchat notifications
      withCompletionHandler()
    } else {
      super.userNotificationCenter(center, didReceive: didReceive, withCompletionHandler: withCompletionHandler)
    }
  }
}```