iOS推送通知:当app处于活动状态时，如何获得推送通知？

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { (granted, error) in
        if granted {
            DispatchQueue.main.async {
                application.registerForRemoteNotifications()
            }
        }
    }
    return true
}

import UserNotifications

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // 注册远程通知权限
        UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { (granted, error) in
            if granted {
                DispatchQueue.main.async {
                    application.registerForRemoteNotifications()
                }
            }
        }
        
        // 设置UNUserNotificationCenterDelegate
        UNUserNotificationCenter.current().delegate = self
        
        return true
    }
    
    // 处理前台收到的推送通知
    func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        // 在前台展示推送通知
        completionHandler([.alert, .sound, .badge])
    }
    
    // 处理后台或者应用程序关闭状态下点击推送通知的操作
    func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {
        // 处理推送通知的点击操作
        completionHandler()
    }
    
    // 注册远程通知成功时调用
    func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
        // 将设备的Device Token发送给服务器，用于推送通知
    }
    
    // 注册远程通知失败时调用
    func application(_ application: UIApplication, didFailToRegisterForRemoteNotificationsWithError error: Error) {
        // 注册远程通知失败的处理
    }
    
    // 处理接收到的远程通知
    func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any]) {
        // 处理接收到的远程通知
    }
}