Detecting iOS Dark Mode Change

Question

I read through the documentation regarding: https://developer.apple.com/documentation/appkit/supporting_dark_mode_in_your_interface

When the user changes the system appearance, the system automatically asks each window and view to redraw itself. During this process, the system calls several well-known methods for both macOS and iOS, listed in the following table, to update your content.

In our legacy app we create our views as lazy variables in the init of each class. This means the views won't get drawn out with the correct color if the user goes into settings and switches to dark mode.

If you make appearance-sensitive changes outside of these methods, your app may not draw its content correctly for the current environment. The solution is to move your code into these methods.

Our application is quite big and a refactor will be done to support this in a better way in the future but I'm wondering if there is a way to detect this changes with the notification center like what can be done for Mac OS:

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

Answer 1

Swift 5:

traitCollectionDidChange also gets called a few times. This is how I detect DarkMode runtime change and setColors().

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)

        setColors()
    }

In setColors() func I update the colors. Detecting current colorScheme:

extension UIViewController {
    var isDarkMode: Bool {
        if #available(iOS 13.0, *) {
            return self.traitCollection.userInterfaceStyle == .dark
        }
        else {
            return false
        }
    }

}

I have colors defined like this (for iOS < 13):

enum ColorCompatibility {
    static var myOlderiOSCompatibleColorName: UIColor {
        if UIViewController().isDarkMode {
            return UIColor(red: 33, green: 35, blue: 37, alpha: 0.85)
        }
        else {
            return UIColor(hexString: "#F3F3F3", alpha: 0.85)
        }
    }
}

Example:

private func setColors() {
  myView.backgroundColor = ColorCompatibility.myOlderiOSCompatibleColorName
}

Also you might need to call setColors in ViewDidLoad/Will/DidAppear depending on your case like this:

viewDidLoad() {
...
setColors()
...
}

For iOS11+ you could use "named Colors", defined in Assets and much easier to use in IB.

Cheers

Answer 2

Just override method form iOS 13 to Detect dark light mode change swift 5.

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)

    if #available(iOS 13.0, *) {
        if self.traitCollection.hasDifferentColorAppearance(comparedTo: previousTraitCollection) {
            if traitCollection.userInterfaceStyle == .dark {
                //Dark
            }
            else {
                //Light
            }
        }
    } else {
        // Fallback on earlier versions
    }
}

traitCollectionDidChange is a method in ViewControllers and Views.

Answer 3

I think for colors is better to use

UIColor.init { (trait) -> UIColor in

    return trait.userInterfaceStyle == .dark ? .label : .black
}

because this way if the system change, the color change too automatically.

Answer 4

Objective-C version:

if (@available(iOS 12.0, *)) {

    if( self.traitCollection.userInterfaceStyle == UIUserInterfaceStyleDark ){
       //is dark
    }else{
        //is light

    }
}

Answer 5

in iOS Swift 5

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
  // Do sonthing
}

Answer 6

iOS 17+

As of iOS 17, the traitCollectionDidChange method has been deprecated. Apple now recommends observing trait changes via one of the registerForTraitChanges APIs. See the latest documentation for more info.

registerForTraitChanges([UITraitUserInterfaceStyle.self]) { (self: Self, previousTraitCollection: UITraitCollection) in
    if self.traitCollection.userInterfaceStyle == .dark {
        // Dark mode
    } else {
        // Light mode
    }
}

Answer 7

If anyone, the application is bothered by calling traitCollectionDidChange twice when it is thrown into the background, the following code block will help. Inactive state is first step for foreground(active) state. So you can handle theme changes at right time.

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)
    
    let userInterfaceStyle = traitCollection.userInterfaceStyle

    if UIApplication.shared.applicationState == .inactive {
        
        switch userInterfaceStyle {
        case .unspecified:
            print("unspecified")
        case .light:
            //Do something for light mode.
            print("Light Mode")
        case .dark:
            //Do something for dark mode.
            print("Dark Mode")
        @unknown default:
            break
        }
    }
}

Answer 8

 override public func tintColorDidChange() {
    super.tintColorDidChange()

    if traitCollection.userInterfaceStyle == .dark {
       ...
    } else {
       ...
    }
 }

Answer 9

I ended up moving all my color setup to layoutSubviews() function in all views and the viewDidLayoutSubviews() in the view controllers.