How to detect switch between macOS default & dark mode using Swift 3

Swift 5, Xcode 10.2.1, macOS 10.14.4

Great stuff. My two cents around @Jeffrey's answer:

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

So one could (instead of rawValue):

func listenToInterfaceChangesNotification() { DistributedNotificationCenter.default.addObserver( self, selector: #selector(interfaceModeChanged), name: .AppleInterfaceThemeChangedNotification, object: nil ) } 

Remember the @objc attribute:

@objc func interfaceModeChanged() { // Do stuff. } 

So, my little additions as well:

enum InterfaceStyle: String { case Light case Dark case Unspecified } extension Notification.Name { static let AppleInterfaceThemeChangedNotification = Notification.Name("AppleInterfaceThemeChangedNotification") } extension NSViewController { var interfaceStyle: InterfaceStyle { let type = UserDefaults.standard.string(forKey: "AppleInterfaceStyle") ?? "Unspecified" return InterfaceStyle(rawValue: type) ?? InterfaceStyle.Unspecified } } 

and somewhere in a NSViewController:

 DistributedNotificationCenter.default.addObserver(forName: .AppleInterfaceThemeChangedNotification, object: nil, queue: OperationQueue.main) { [weak weakSelf = self] (notification) in // add an observer for a change in interface style weakSelf?.setAppearance(toStyle: weakSelf!.interfaceStyle) } 

where setAppearance reacts on the change of style.

If you simply need to update icon images for dark mode, you can do this without notifications by creating a dynamic image that updates automatically.

From Apple's documentation:

To create an image that draws its content dynamically, use the init(size:flipped:drawingHandler:) method to initialize your image with a custom drawing handler block. AppKit calls your handler block whenever the system appearance changes, giving you a chance to redraw the image using the new appearance.