Building macOS dark mode app on 10.13.6/Xcode 10

Question

I have a macOS app that uses some image assets specifically for the new dark mode on macOS 10.14. I noticed that when I build the app on Xcode 10 on macOS 10.14 beta, dark mode works correctly. However, when I build the same codebase on Xcode 10 on macOS 10.13.6 and copy it to a macOS 10.14 beta machine, the "Any" resources are used and the user interface looks incorrect.

I can confirm I'm using the same 10.14 SDK in both cases.

I took a look at my app bundles, and noticed that the one built on 10.13.6 has a smaller Contents/Resources/Assets.car file.

Can anyone reproduce this behaviour, and if so, is it expected that I will only be able to build apps supporting dark mode on 10.14? Because that does not make sense to me - Xcode 10 has all the same options for dark mode assets, and as I said I'm using the same SDK in both cases. And I would like to not have to use a beta macOS (and later this month, a brand new macOS) to build this app.

Answer 1

I was poking around in the build log, and I found this message:

"Varying images and colors by appearance requires building on macOS 10.14 or later"

So, I have my answer. This is expected behaviour, and you can only build apps with images specifically supporting dark mode on macOS 10.14 or later.