Why doesn't my UILabel change when I press the button? - swift

Question

By pressing a button in my app, the value of a variable falls by 3. While this happens without any issues, the label which uses string interpolation to show that variable as its text (label.text) does not reflect the change.
How can I make it so pressing the button changes the value of the UILabel?
import UIKit
class ViewController: UIViewController {
var token = 5
let theButton: UIButton = {
let button = UIButton(type: .system)
button.setTitle("button", for: .normal)
button.backgroundColor = .systemPink
button.addTarget(self, action: #selector(theButtonPressed), for: .touchUpInside)
button.translatesAutoresizingMaskIntoConstraints = false
return button
}()
#objc func theButtonPressed() {
if token >= 3 {
token -= 3
print("ok done")
} else {
print("nope")
}
}
lazy var tokenLabel: UILabel = {
let label = UILabel()
label.text = "\(token)"
label.translatesAutoresizingMaskIntoConstraints = false
return label
}()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .systemBlue
view.addSubview(tokenLabel)
view.addSubview(theButton)
theButton.heightAnchor.constraint(equalToConstant: 100).isActive = true
theButton.widthAnchor.constraint(equalToConstant: 200).isActive = true
theButton.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
theButton.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
tokenLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: 60).isActive = true
tokenLabel.heightAnchor.constraint(equalToConstant: 300).isActive = true
tokenLabel.widthAnchor.constraint(equalToConstant: 200).isActive = true
tokenLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
}
}

Answer 1

You need to update the label's text when the button is pressed.
#objc func theButtonPressed() {
if token >= 3 {
token -= 3
print("ok done")
tokenLabel.text = "\(token)" // <- update
} else {
print("nope")
}
}
Or, you can observe the property token and change the label when a new value is set.
var token = 5 {
didSet {
tokenLabel.text = "\(token)"
}
}
#objc func theButtonPressed() {
if token >= 3 {
token -= 3
print("ok done")
} else {
print("nope")
}
}