How to detect your iOS app is running on macOS Catalyst

Swift version: 5.10

Paul Hudson @twostraws October 4th 2019

Although Catalyst does a good job of making UIKit work on macOS, you will quickly realize that some things that worked great on iOS just aren’t great fits for macOS.

So, if you want to detect when your iOS app is running on macOS using Catalyst, you can add an #if targetEnvironment check to provide alternative functionality, like this:

#if targetEnvironment(macCatalyst)
    print("UIKit running on macOS")
#else
    print("Your regular code")
#endif

If that file also happens to support other platforms such as watchOS and tvOS, you can add further checks as needed like this:

#if targetEnvironment(macCatalyst)
    print("UIKit running on macOS")
#elseif os(watchOS)
    print("Running on watchOS")
#else
    print("Your regular code")
#endif

Detecting Catalyst is particularly useful when removing behavior that, while appropriate on iOS itself, doesn’t look great on macOS. For example, having screens full of information slide onto a UINavigationController looks great on iPhone, OK on iPad, but downright ugly on macOS, so you might want to push view controllers without animation when running on Catalyst.