在swift中创建秒表

import UIKit

class ViewController: UIViewController {
    var timer: Timer?
    var startTime: Date?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let startButton = UIButton(frame: CGRect(x: 100, y: 100, width: 100, height: 50))
        startButton.setTitle("Start", for: .normal)
        startButton.setTitleColor(.blue, for: .normal)
        startButton.addTarget(self, action: #selector(startButtonTapped), for: .touchUpInside)
        view.addSubview(startButton)
        
        let stopButton = UIButton(frame: CGRect(x: 100, y: 200, width: 100, height: 50))
        stopButton.setTitle("Stop", for: .normal)
        stopButton.setTitleColor(.red, for: .normal)
        stopButton.addTarget(self, action: #selector(stopButtonTapped), for: .touchUpInside)
        view.addSubview(stopButton)
    }
    
    @objc func startButtonTapped() {
        startTime = Date()
        timer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: #selector(updateTimer), userInfo: nil, repeats: true)
    }
    
    @objc func stopButtonTapped() {
        timer?.invalidate()
        timer = nil
    }
    
    @objc func updateTimer() {
        if let startTime = startTime {
            let currentTime = Date()
            let elapsedTime = currentTime.timeIntervalSince(startTime)
            
            let minutes = Int(elapsedTime / 60)
            let seconds = Int(elapsedTime.truncatingRemainder(dividingBy: 60))
            let milliseconds = Int((elapsedTime * 100).truncatingRemainder(dividingBy: 100))
            
            print(String(format: "%02d:%02d:%02d", minutes, seconds, milliseconds))
        }
    }
}