UILabel isn't Displaying at Center of View - Xcode Playground - swift

Question

I have the following code running on Xcode Playground. However, even though I specify that the label is centered at the center of the view, it doesn't appear there.
import UIKit
import PlaygroundSupport
class TestViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = UIColor.white
let label = UILabel(frame: CGRect(x: 0, y: 0, width: 100, height: 20))
label.center = CGPoint(x: view.frame.width / 2, y: view.frame.height / 2)
label.text = "Hello World!"
label.textColor = UIColor.black
view.addSubview(label)
}
}
PlaygroundPage.current.liveView = TestViewController()

Answer 1

The view controller's view's frame is not final in viewDidLoad.
You either need to set the label's autoresizingMask or apply constraints to keep it in the center.
And since you made the label wider than the text, you also need to set the label's textAlignment to center.
let label = UILabel(frame: CGRect(x: 0, y: 0, width: 100, height: 20))
label.center = view.center
label.text = "Hello World!"
label.textColor = .black
label.textAlignment = .center // or call label.sizeToFit()
label.autoresizingMask = [ .flexibleTopMargin, .flexibleBottomMargin, .flexibleLeftMargin, .flexibleRightMargin, ]
view.addSubview(label)

Answer 2

view frame is not finalized when viewDidLoad is triggered, you need to set the frame of the label inside the method viewDidLayoutSubviews as this method is being invoked when view bound was finalized.
Try
class TestViewController: UIViewController {
let label = UILabel(frame: CGRect(x: 0, y: 0, width: 100, height: 20))
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = UIColor.white
label.text = "Hello World!"
label.textColor = UIColor.black
self.view.addSubview(label)
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
self.label.center = self.view.center
}
}