How to add constraints programmatically using Swift

Question

I\'m trying to figure this out since last week without going any step further. Ok, so I need to apply some constraints programmatically

Answer 1

Constraints for multiple views in playground.

swift 3+

  var yellowView: UIView!
    var redView: UIView!

    override func loadView() {

        // UI

        let view = UIView()
        view.backgroundColor = .white

        yellowView = UIView()
        yellowView.backgroundColor = .yellow
        view.addSubview(yellowView)

        redView = UIView()
        redView.backgroundColor = .red
        view.addSubview(redView)

        // Layout
        redView.translatesAutoresizingMaskIntoConstraints = false
        yellowView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            yellowView.topAnchor.constraint(equalTo: view.topAnchor, constant: 20),
            yellowView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 20),
            yellowView.widthAnchor.constraint(equalToConstant: 80),
            yellowView.heightAnchor.constraint(equalToConstant: 80),

            redView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -20),
            redView.trailingAnchor.constraint(equalTo: view.trailingAnchor,constant: -20),
            redView.widthAnchor.constraint(equalToConstant: 80),
            redView.heightAnchor.constraint(equalToConstant: 80)
            ])

        self.view = view
    }

In my opinion xcode playground is the best place for learning adding constraints programmatically.