SWIFT

swift add programmatically constraint to view

// Swift3+
let imageView = UIImageView()
imageView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
  imageView.widthAnchor.constraint(equalToConstant: 16),
  imageView.heightAnchor.constraint(equalToConstant: 16),
])
self.addSubview(self.imageView)

swift edit constraint programmatically

yourHeightConstraintOutlet.constant = someValue
yourView.layoutIfNeeded()