iOS 在一段时间不活动后执行操作（无用户交互）

如何在 iOS 应用中实现一段时间不活动后执行操作

swift
import UIKit
class ViewController: UIViewController {
    var timer: Timer?
    override func viewDidLoad() {
        super.viewDidLoad()
        
        NotificationCenter.default.addObserver(self, selector: #selector(willResignActive), name: UIApplication.willResignActiveNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(didBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
    }
    @objc func willResignActive() {
        timer?.invalidate()
        timer = Timer.scheduledTimer(withTimeInterval: 60.0, repeats: false, block: { (_) in
            self.showAlert()
        })
    }
    
    @objc func didBecomeActive() {
        timer?.invalidate()
    }
    
    func showAlert() {
        let alert = UIAlertController(title: "提示", message: "您已经一段时间没有操作了，请注意休息。", preferredStyle: .alert)
        let okAction = UIAlertAction(title: "确定", style: .default, handler: nil)
        alert.addAction(okAction)
        present(alert, animated: true, completion: nil)
    }
    
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
}