How to force a view controller to use light or dark mode

Swift version: 5.6

Paul Hudson @twostraws June 3rd 2019

By default all instances of UIViewController are set to automatically adapt their color appearance to match the user’s system preferences, but if you want you can force some or all of your app to use light or dark mode by setting the overrideUserInterfaceStyle property of your view controller to .light or .dark.

For example:

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        overrideUserInterfaceStyle = .dark    
    }
}

This setting exists on other containers, such as UIWindow and UIView, and the value of this property cascades to everything inside the thing you change. So, if you set your main UIWindow to always have dark mode, then all view controllers and views inside it will always have dark mode.