如何在app打开时使推送通知出现在前台

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // 注册远程推送通知
    UNUserNotificationCenter.current().delegate = self
    UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { (granted, error) in
        if granted {
            DispatchQueue.main.async {
                application.registerForRemoteNotifications()
            }
        }
    }
    return true
}

extension AppDelegate: UNUserNotificationCenterDelegate {
    func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        // 自定义推送通知的展示方式
        completionHandler([.alert, .sound, .badge])
    }
}

UNUserNotificationCenter.current().getDeliveredNotifications { (notifications) in
    for notification in notifications {
        // 处理推送通知
    }
}