要实现本地通知与倒计时功能，可以使用以下步骤：

1. 导入相关的库

   import UIKit
   import UserNotifications
   

2. 请求用户授权通知权限

   UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { (granted, error) in
       if granted {
           print("用户授权通知权限")
       }
   }
   

3. 创建本地通知

   func createLocalNotification(withTitle title: String, andBody body: String, afterDelay delay: TimeInterval) {
       let content = UNMutableNotificationContent()
       content.title = title
       content.body = body
       content.sound = UNNotificationSound.default
       
       let trigger = UNTimeIntervalNotificationTrigger(timeInterval: delay, repeats: false)
       let request = UNNotificationRequest(identifier: "LocalNotification", content: content, trigger: trigger)
       
       UNUserNotificationCenter.current().add(request) { (error) in
           if let error = error {
               print("创建本地通知失败：\(error.localizedDescription)")
           }
       }
   }
   

4. 创建倒计时功能

   var countdownTimer: Timer?
   var remainingTime = 60
   
   func startCountdown() {
       countdownTimer?.invalidate()
       countdownTimer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(updateCountdown), userInfo: nil, repeats: true)
   }
   
   @objc func updateCountdown() {
       if remainingTime > 0 {
           remainingTime -= 1
           print("倒计时剩余时间：\(remainingTime)")
       } else {
           countdownTimer?.invalidate()
           print("倒计时结束")
       }
   }
   

5. 调用上述方法

   // 创建本地通知并在5秒后发送
   createLocalNotification(withTitle: "本地通知", andBody: "这是一个本地通知示例", afterDelay: 5)
   
   // 启动倒计时
   startCountdown()
   

上述代码示例了如何创建本地通知并在指定的延迟时间后发送，以及如何创建一个倒计时功能。你可以根据自己的需求进行修改和扩展。