At what stage of code execution do you define and apply constraints?

Constraints in iOS development are usually defined and applied during the user interface building phase, that is, during the setup and layout of views.

This can occur:

• In Interface Builder (Storyboard or XIB), where constraints are set visually.
• In code, typically in viewDidLoad methods or during view initialization, where NSLayoutConstraint objects are created and activated.

Constraints are applied before the interface is displayed so that the system can correctly calculate the sizes and positions of elements when layout procedures are called.

Example of creating and activating constraints in code:

let button = UIButton()
button.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(button)
NSLayoutConstraint.activate([
    button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
    button.centerYAnchor.constraint(equalTo: view.centerYAnchor),
    button.widthAnchor.constraint(equalToConstant: 100),
    button.heightAnchor.constraint(equalToConstant: 50)
])