What is the UIAppearance proxy?

Swift version: 5.4

Paul Hudson @twostraws May 28th 2019

If you need to make broad changes to UIKit components, the UIAppearance proxy is your friend: you can treat it like an instance of any given UIKit type, except the changes you make there apply to all new instances of that type. Note: it applies to new instances of that, and won’t change any existing instances you have created.

For example, if you want all navigation bars to have a red background color regardless of where they appear in your app, you could put this into the didFinishLaunching method of your app delegate:

UINavigationBar.appearance().barTintColor = .red

For more precise changes you can use appearance(whenContainedInInstancesOf:) and specify a container appearance proxy. For example, you might want to make bar button items one color when they appear in navigation bars and another color when they appear in toolbars:

UIBarButtonItem.appearance(whenContainedInInstancesOf: [UINavigationBar.self]).tintColor = .green
UIBarButtonItem.appearance(whenContainedInInstancesOf: [UIToolbar.self]).tintColor = .red

While that’s easy to do, I hope you at least choose better colors!