Protocols & Delegation in Swift (Sample)

MenuViewController.swift

protocol Customizable {
  func hideMenu()
  func isDarkModeActive()
  func setDarkMode(_ mode: Bool)
}

class MenuViewController: NSViewController {
  weak var delegate: Customizable?
  
  override func viewDidLoad() {
    super.viewDidLoad()
    let mode = delegate?.isDarkModeActive()
    delegate?.setDarkMode(mode)
  }
  
  @IBAction func closeMenuAction(_ sender: NSButton) {
    delegate?.hideMenu()
  }
  ...
}

ViewController.swift

class ViewController: NSViewController, Customizable {
  
  @IBOutlet var menuView: NSView!
  let menuController = MenuViewController()
  
  override func viewDidLoad() {
    super.viewDidLoad()
    menuController.delegate = self
  }
  
  func hideMenu() {
    menuView.isHidden = true
  }
  
  func setDarkMode(_ mode: Bool) {
    let darkMode = NSAppearance(named: .darkAqua)
    let lightMode = NSAppearance(named: .aqua)
    
    if mode { NSApplication.shared.appearance = darkMode }
    else { NSApplication.shared.appearance = lightMode }
  }
  
  func isDarkModeActive() -> Bool {
    if InterfaceStyle() == .Dark { return true }
    else { return false }
  }
  ...
}