How do I add constraints programmatically to my UILabel - swift

Question

Is there a way in swift to have a label and make constraints for it programmatically. For example on all devices to 'Pin to the top' or 'Pin to the right side' so that on all devices it just pins to whatever device is being used.
It's because I've created a label programmatically, so I want to make constraints for it.
If you need more info, just let me know. Thanks :)

Answer 1

override func viewDidLoad() {
super.viewDidLoad()
let label = UILabel()
self.view.addSubview(label)
label.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
label.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
label.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
label.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true
}
This will bind the item to all the edges, making it as big as the screen. Anchor is used to refer to an point in game. which is either its superview or some view on the same level as your current view. You can use references as i did self.view.trailingAnchor, and you can also add offsets and insets view.leadingAnchor.constraint(equalTo: self.view.leadingAnchor, constant: 8).isActive = true. Or you can name the direct size of something label.heightAnchor.constraint(equalToConstant: CGFloat).isActive = true. Good luck

Answer 2

You can easily add Constraints programatically using NSLayoutConstraints. Below is the code sample for it. I have used centering constraint , you can use leading and top constraints with height and width.
func addLabel(){
let newView =UILabel()
self.view.addSubview(newView)
newView.translatesAutoresizingMaskIntoConstraints = false
let horizontalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0)
let verticalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0)
let widthConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100)
let heightConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100)
NSLayoutConstraint.activate([horizontalConstraint, verticalConstraint, widthConstraint, heightConstraint])
}

Answer 3

the code below, will stick your label to top-right as you want, on all d devices,
let aLabel = UILabel()
self.view.addSubview(aLabel)
aLabel.backgroundColor = UIColor.gray
aLabel.text = " i am a label"
aLabel.textAlignment = .center
aLabel.translatesAutoresizingMaskIntoConstraints = false
let horizontalConstraint = NSLayoutConstraint(item: aLabel, attribute: NSLayoutAttribute.trailing, relatedBy: NSLayoutRelation.equal, toItem: view, attribute:NSLayoutAttribute.trailing, multiplier: 1, constant: 0)
let verticalConstraint = NSLayoutConstraint(item: aLabel, attribute: NSLayoutAttribute.top, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.top, multiplier: 1, constant: 0)
NSLayoutConstraint.activate([horizontalConstraint, verticalConstraint])
self.view.layoutIfNeeded()