ios-theme.md

iOS theme code

enum Theme: Int {
  //1
  case `default`, dark, graphical

  //2
  private enum Keys {
    static let selectedTheme = "SelectedTheme"
  }

  //3
  static var current: Theme {
    let storedTheme = UserDefaults.standard.integer(forKey: Keys.selectedTheme)
    return Theme(rawValue: storedTheme) ?? .default
  }


  var mainColor: UIColor {
    switch self {
    case .default:
      return UIColor(red: 87.0/255.0, green: 188.0/255.0, blue: 95.0/255.0, alpha: 1.0)
    case .dark:
      return UIColor(red: 255.0/255.0, green: 115.0/255.0, blue: 50.0/255.0, alpha: 1.0)
    case .graphical:
      return UIColor(red: 10.0/255.0, green: 10.0/255.0, blue: 10.0/255.0, alpha: 1.0)
    }
  }

  func apply() {
    //1
    UserDefaults.standard.set(rawValue, forKey: Keys.selectedTheme)
    UserDefaults.standard.synchronize()

    //2
    UIApplication.shared.delegate?.window??.tintColor = mainColor

    UINavigationBar.appearance().barStyle = barStyle
    UINavigationBar.appearance().setBackgroundImage(navigationBackgroundImage, for: .default)

    UINavigationBar.appearance().backIndicatorImage = UIImage(named: "backArrow")
    UINavigationBar.appearance().backIndicatorTransitionMaskImage = UIImage(named: "backArrowMaskFixed")

    UITabBar.appearance().barStyle = barStyle
    UITabBar.appearance().backgroundImage = tabBarBackgroundImage

    let tabIndicator = UIImage(named: "tabBarSelectionIndicator")?.withRenderingMode(.alwaysTemplate)
    let tabResizableIndicator = tabIndicator?.resizableImage(
      withCapInsets: UIEdgeInsets(top: 0, left: 2.0, bottom: 0, right: 2.0))
    UITabBar.appearance().selectionIndicatorImage = tabResizableIndicator

    let controlBackground = UIImage(named: "controlBackground")?
      .withRenderingMode(.alwaysTemplate)
      .resizableImage(withCapInsets: UIEdgeInsets(top: 3, left: 3, bottom: 3, right: 3))

    let controlSelectedBackground = UIImage(named: "controlSelectedBackground")?
      .withRenderingMode(.alwaysTemplate)
      .resizableImage(withCapInsets: UIEdgeInsets(top: 3, left: 3, bottom: 3, right: 3))

    UISegmentedControl.appearance().setBackgroundImage(controlBackground,
                                                       for: .normal,
                                                       barMetrics: .default)
    UISegmentedControl.appearance().setBackgroundImage(controlSelectedBackground,
                                                       for: .selected,
                                                       barMetrics: .default)

    UIStepper.appearance().setBackgroundImage(controlBackground, for: .normal)
    UIStepper.appearance().setBackgroundImage(controlBackground, for: .disabled)
    UIStepper.appearance().setBackgroundImage(controlBackground, for: .highlighted)
    UIStepper.appearance().setDecrementImage(UIImage(named: "fewerPaws"), for: .normal)
    UIStepper.appearance().setIncrementImage(UIImage(named: "morePaws"), for: .normal)

    UISlider.appearance().setThumbImage(UIImage(named: "sliderThumb"), for: .normal)
    UISlider.appearance().setMaximumTrackImage(UIImage(named: "maximumTrack")?
      .resizableImage(withCapInsets:UIEdgeInsets(top: 0, left: 0.0, bottom: 0, right: 6.0)), for: .normal)

    UISlider.appearance().setMinimumTrackImage(UIImage(named: "minimumTrack")?
      .withRenderingMode(.alwaysTemplate)
      .resizableImage(withCapInsets:UIEdgeInsets(top: 0, left: 6.0, bottom: 0, right: 0)), for: .normal)

    UISwitch.appearance().onTintColor = mainColor.withAlphaComponent(0.3)
    UISwitch.appearance().thumbTintColor = mainColor

    UITableViewCell.appearance().backgroundColor = backgroundColor
    UILabel.appearance(whenContainedInInstancesOf: [UITableViewCell.self]).textColor = textColor

  }

  var barStyle: UIBarStyle {
    switch self {
    case .default, .graphical:
      return .default
    case .dark:
      return .black
    }
  }

  var navigationBackgroundImage: UIImage? {
    return self == .graphical ? UIImage(named: "navBackground") : nil
  }

  var tabBarBackgroundImage: UIImage? {
    return self == .graphical ? UIImage(named: "tabBarBackground") : nil
  }

  var backgroundColor: UIColor {
    switch self {
    case .default, .graphical:
      return UIColor.white
    case .dark:
      return UIColor(white: 0.4, alpha: 1.0)
    }
  }

  var textColor: UIColor {
    switch self {
    case .default, .graphical:
      return UIColor.black
    case .dark:
      return UIColor.white
    }
  }


}

Reference: https://www.raywenderlich.com/156036/uiappearance-tutorial-getting-started