如何在swift中从剩余时间运行coutdown时间？

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var countdownLabel: UILabel!
    
    var countdownTimer: Timer?
    var remainingTime: TimeInterval = 60 // 设置倒计时的总时间
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        startCountdown()
    }
    
    func startCountdown() {
        countdownTimer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(updateCountdown), userInfo: nil, repeats: true)
    }
    
    @objc func updateCountdown() {
        if remainingTime > 0 {
            remainingTime -= 1
            countdownLabel.text = formatTime(remainingTime)
        } else {
            countdownTimer?.invalidate()
            countdownTimer = nil
            countdownLabel.text = "倒计时结束"
        }
    }
    
    func formatTime(_ time: TimeInterval) -> String {
        let minutes = Int(time) / 60
        let seconds = Int(time) % 60
        return String(format: "%02d:%02d", minutes, seconds)
    }
}