swift programmatically add constraints code example

Example 1: swift set constraint programmatically

override func viewDidLoad() {
    let newView = UIView()
    newView.backgroundColor = UIColor.red
    view.addSubview(newView)

    newView.translatesAutoresizingMaskIntoConstraints = false
    NSLayoutConstraint(item: newView, attribute: NSLayoutConstraint.Attribute.centerX, relatedBy: NSLayoutConstraint.Relation.equal, toItem: view, attribute: NSLayoutConstraint.Attribute.centerX, multiplier: 1, constant: 0).isActive = true
    NSLayoutConstraint(item: newView, attribute: NSLayoutConstraint.Attribute.centerY, relatedBy: NSLayoutConstraint.Relation.equal, toItem: view, attribute: NSLayoutConstraint.Attribute.centerY, multiplier: 1, constant: 0).isActive = true
    NSLayoutConstraint(item: newView, attribute: NSLayoutConstraint.Attribute.width, relatedBy: NSLayoutConstraint.Relation.equal, toItem: nil, attribute: NSLayoutConstraint.Attribute.notAnAttribute, multiplier: 1, constant: 100).isActive = true
    NSLayoutConstraint(item: newView, attribute: NSLayoutConstraint.Attribute.height, relatedBy: NSLayoutConstraint.Relation.equal, toItem: nil, attribute: NSLayoutConstraint.Attribute.notAnAttribute, multiplier: 1, constant: 100).isActive = true
}

Example 2: swift constraints programmatically

import UIKit

class ViewController: UIViewController {

override func viewDidLoad() {
super.viewDidLoad()

let myImageView:UIImageView = UIImageView()
myImageView.backgroundColor = UIColor.red
myImageView.image = UIImage(named:"sample_dog")!
myImageView.translatesAutoresizingMaskIntoConstraints = false
myImageView.layer.borderColor = UIColor.red.cgColor
myImageView.layer.borderWidth = 10
self.view.addSubview(myImageView)
        
view.removeConstraints(view.constraints)


view.addConstraint(NSLayoutConstraint(
item: myImageView,
attribute: .top,
relatedBy: .equal,
toItem: view,
attribute: .top,
multiplier: 1,
constant:100)
    
)

view.addConstraint(NSLayoutConstraint(
item: myImageView,
attribute: .centerX,
relatedBy: .equal,
toItem: view,
attribute: .centerX,
multiplier: 1,
constant:0)
)
    
view.addConstraint(NSLayoutConstraint(
item: myImageView,
attribute: .height,
relatedBy: .equal,
toItem: view,
attribute: .width,
multiplier: 0.5,
constant:40))
    
view.addConstraint(NSLayoutConstraint(
item: myImageView,
attribute: .width,
relatedBy: .equal,
toItem: view,
attribute: .width,
multiplier: 0.5,
constant:40))
    
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}
}