ProgrammaticUIKitSnippets.swift

// programmatic view controller
/*
 usage:
 
 override func viewDidLoad() {
     super.viewDidLoad()
     
     let newViewController = NewViewController(string: "Hello")
     addChildViewController(newViewController, in: view)
 }
 */
class NewViewController: UIViewController {
    var string: String
    
    init(string: String) {
        self.string = string
        super.init(nibName: nil, bundle: nil)
    }
    
    override func loadView() {
        view = UIView()
    }
    
    // you can add other methods like `viewDidLoad` here
    
    // this method is boilerplate code but you always need to include it
    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

// useful extensions, including `addChildViewController`
extension UIViewController {
    // add a view controller as a *subview*
    func addChildViewController(_ childViewController: UIViewController, in view: UIView) {
        addChild(childViewController)
        view.addSubview(childViewController.view)
        
        /// Configure child view
        childViewController.view.frame = view.bounds
        childViewController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        
        /// Notify child view controller
        childViewController.didMove(toParent: self)
    }
    
    func removeChildViewController(_ childViewController: UIViewController) {
        /// Notify child view controller
        childViewController.willMove(toParent: nil)
        
        /// Remove child view from superview
        childViewController.view.removeFromSuperview()
        
        /// Notify child view controller again
        childViewController.removeFromParent()
    }
}

// lifesaver extension for pinning a view to its parent
extension UIView {
    func pinEdgesToSuperview() {
        guard let superview = superview else { return }
        self.translatesAutoresizingMaskIntoConstraints = false // always remember this!
        NSLayoutConstraint.activate([
            self.topAnchor.constraint(equalTo: superview.topAnchor),
            self.rightAnchor.constraint(equalTo: superview.rightAnchor),
            self.bottomAnchor.constraint(equalTo: superview.bottomAnchor),
            self.leftAnchor.constraint(equalTo: superview.leftAnchor)
        ])
    }
}

// useful for debugging
extension UIView {
    /// add a border to a view
    /// usage: `view.addDebugBorders(.red)`
    func addDebugBorders(_ color: UIColor, width: CGFloat = 0.75) {
        backgroundColor = color.withAlphaComponent(0.2)
        layer.borderColor = color.cgColor
        layer.borderWidth = width
    }
}