bounds of a UIView changes after viewDidLoad - ios

Question

I have a view with a number of subviews. The subviews all have size constraints, built in the storyboard.
part of viewDidLoad() is to programmatically add a number of buttons. And I'm using the subview's bounds to known where to add the buttons to take up available screen real estate. As a simplified example:
override func viewDidLoad()
{
super.viewDidLoad()
let bottom = buttonView.bounds.maxY
let right = buttonView.bounds.maxX
let button = UIButton()
button.frame = CGRect(x: CGFloat(0.0),
y: CGFloat(0.0),
width: CGFloat(right),
height: CGFloat(bottom))
button.addTarget(self, action: #selector(buttonPushed(_:)), for: .touchUpInside)
buttonView.addSubview(button)
print("buttonview frame = \(buttonView.frame)")
}
override func viewWillAppear()
{
super.viewWillAppear()
print("buttonview frame = \(buttonView.frame)")
}
What I see happen in the simulator (and on hardware) is that the views are all sized according to how I had it designed in the storyboard, matching the hardware I had designed it on (iPhone 11). When I run it on an iPhone 8, my subviews all run off screen, and the first print statement indicates a width of 414.0. The constraints are applied sometime before viewWillAppear, and the second print statement indicates a width of 375.0. But my button isn't resized to fit. It still continues off screen.
How do I programmatically add my button subviews (this example only has the 1, code has 20 being built in a loop) to adhere to the constraints of the superview bounds, after I know what they actually are?

Answer 1

you have to add constraint by code, for example.
1) first I will create the button.
lazy var closeButton : UIButton = {
let button = UIButton(type: .custom)
button.translatesAutoresizingMaskIntoConstraints = false
button.backgroundColor = .blue
button.addTarget(self, action: #selector(buttonAction), for: .touchUpInside)
return button
}()
2) with this code I will add the button to the main view, and set the constraint.
self.view.addSubview(closeButton)
NSLayoutConstraint.activate([
closeButton.heightAnchor.constraint(equalToConstant: 20),
closeButton.widthAnchor.constraint(equalToConstant: 20),
closeButton.trailingAnchor.constraint(equalTo: self.view.trailingAnchor, constant: -20),
closeButton.centerYAnchor.constraint(equalTo: self.view.centerYAnchor)]
but if you want to understand really how work this please the follow link
How to add constraints programmatically using Swift