iOS Timer 구현하기

class ViewController: UIViewController {
	let timerLabel = UILabel()
	var timer: Timer!
	var seconds = 1000

	override func viewDidLoad() {
		super.viewDidLoad()
		self.initialize()
	}

	override func viewWillAppear(_ animater: Bool) {
		super.viewWillAppear(animated)
		
		self.timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in
			if self.seconds > 0 {
				self.seconds -=1
			}

			let minute = self.seconds / 60
			let second = self.seconds % 60
			let minuteString = "\(minute < 10 ? "0" : "")\(minute)"
			let secondString = "\(second < 10 ? "0" : "")\(second)"
			self.timerLabel.text = "\(minuteString):\(secondString)"
		}
		self.timer.fire() // timer 시작
	}
	// 다른 뷰가 나타났을 때 타이머를 없애주기 위해
	override func viewWillDisappear(_ animated: Bool) {
		super.viewWillDisappear(animated)
		self.timer = nil
	}
}

func initialize() {
	timerLabel.text = "00:00"
	timerLabel.font = UIFont.systemFont(ofSize: 40.0)
	timerLabel.textColor = .black
	timerLabel.sizeToFit() // 자동으로 Label의 모양이 글씨 크기에 맞춰진다.
	timerLabel.center = CGPoint(
		x: UIScreen.main.bounds.width / 2,
		y: UIScreen.main.bounds.height / 2
	)
	self.view.addSubview(timerLabel)
}