iOS Theme

Theme.swift

import UIKit

enum Theme {
    case light
    case dark
}

extension Theme {
    var defaultTextColor: UIColor {
        switch self {
        case .light:
            return .black
        case .dark:
            return .white
        }
    }
}

let ThemeDidChangeNotificationThemeUserInfoKey = "theme"

extension Notification.Name {
    static let ThemeDidChange = Notification.Name("ThemeDidChange")
}

NotificationCenter.default.post(name: .ThemeDidChange, object: nil, userInfo: [
    ThemeDidChangeNotificationThemeUserInfoKey : Theme.dark,
    ])

class View: UIView {

    override init(frame: CGRect) {
        super.init(frame: frame)
        NotificationCenter.default.addObserver(self, selector: #selector(themeDidChange(_:)), name: .ThemeDidChange, object: nil)
    }

    @objc private func themeDidChange(_ notification: Notification) {
        self.theme = notification.userInfo![ThemeDidChangeNotificationThemeUserInfoKey] as! Theme
    }

    private var theme: Theme = .light {
        didSet {
            self.textLabel.textColor = self.theme.defaultTextColor
            // ...
        }
    }
}