Updating multiple UI Elements inside Timer.scheduledTimer doesn't work - ios

Question

I am trying to make an image "move down" every second while also showing a time counter. I have a scheduledTimer where I change the image's Y center and update the timer. The timer label updates but the image does not move. Strangely I can get the image to move down if I comment the line where I update the timer's UILabel. So apparently I can't update both.
I have tried adding the Timer to RunLoop, using a DispatchQueue and creating a Timer that takes a selector but nothing works.
class ViewController: UIViewController {
let starImage = UIImageView(image: UIImage(systemName: "star.fill"))
let timerLabel = UILabel()
var counter = 0
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .black
setupViews()
gameEngine()
}
private func setupViews() {
view.addSubview(starImage)
starImage.tintColor = .systemYellow
starImage.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(timerLabel)
timerLabel.tintColor = .white
timerLabel.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
starImage.heightAnchor.constraint(equalToConstant: 100),
starImage.widthAnchor.constraint(equalToConstant: 100),
starImage.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
starImage.centerXAnchor.constraint(equalTo: view.centerXAnchor),
timerLabel.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 20),
timerLabel.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20),
])
}
// PROBLEM HERE
private func gameEngine() {
Timer.scheduledTimer(withTimeInterval: 1, repeats: true) {
[weak self] _ in
self?.counter += 1
self?.timerLabel.text = "Timer: \(self!.counter)"
self?.starImage.center.y += 10
}
}
}
I got it to work by using UIView.animate as Rob suggested it in the comments.
I replaced the line where I updated the Y value with this:
UIView.animate(withDuration: 1, animations: {
[weak self] in
self?.starImage.transform = CGAffineTransform(translationX: 0, y: CGFloat(self!.counter*100))
})

Answer 1

There are 2 issues:
Instead
timerLabel.tintColor = .white you need to use timerLabel.textColor = .white
2.To move starImage you need update constraint:
class ViewController: UIViewController {
let starImage = UIImageView(image: UIImage(systemName: "star.fill"))
let timerLabel = UILabel()
var counter = 0
var topConstraint: NSLayoutConstraint?
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .black
setupViews()
gameEngine()
}
private func setupViews() {
view.addSubview(starImage)
starImage.tintColor = .systemYellow
starImage.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(timerLabel)
timerLabel.tintColor = .white
timerLabel.textColor = .white
timerLabel.translatesAutoresizingMaskIntoConstraints = false
topConstraint = starImage.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor)
NSLayoutConstraint.activate([
starImage.heightAnchor.constraint(equalToConstant: 100),
starImage.widthAnchor.constraint(equalToConstant: 100),
topConstraint!,
starImage.centerXAnchor.constraint(equalTo: view.centerXAnchor),
timerLabel.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 20),
timerLabel.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20),
])
}
// PROBLEM HERE
private func gameEngine() {
Timer.scheduledTimer(withTimeInterval: 1, repeats: true) {
[weak self] _ in
self?.counter += 1
self?.timerLabel.text = "Timer: \(self!.counter)"
self!.topConstraint?.constant += 10
}
}
}