Docs don't mention that previews only work in debug builds

[CraigSiemens]

I was curious if I'd be able to show the gallery in the TestFlight build of our app to simplify sharing it with designers. I suspected it wouldn't work since Xcode should be removing the previews as part of the optimization, but this tool has enough magic in it, I wasn't 100% sure. I couldn't find it mentioned in the readme one way or the other.

I made a release build and ran it on the simulator and confirmed that no previews were shown in the gallery.

It would be a nice improvement if the readme mentioned that it the gallery only works for debug builds. Also potentially including instructions for removing this as a dependency for release builds since it's not useable and potentially leads to a larger app size.

[noahsmartin]

Hey @CraigSiemens this depends on exactly how you write your previews and what build settings you use. For example you could do this:

#if DEBUG
struct MyPreviews: PreviewProvider { ... }
#endif

And then it would only be included when DEBUG=1 but you could also replace DEBUG with something like ALPHA and have a config that enables them.

Alternatively you could use dead code stripping to remove previews, then you can create a new build config that turns off dead code stripping but has whatever other settings you need. I've heard from other users that a common setup is to have debug/alpha build configs that include previews and other internal-only features, and then an App Store config that only has production features.

[CraigSiemens]

After experimenting with the DemoApp some more, it appears that previews are removed with the following build settings. All I changed was the scheme's run build configuration to Release.

These are the settings that seems to control removing the previews. Changing either one will cause the previews to be present again.

SWIFT_COMPILATION_MODE = wholemodule
SWIFT_OPTIMIZATION_LEVEL = -O

None of the previews are in a #if DEBUG so that doesn't have any effect.

It also appears like DEAD_CODE_STRIPPING is set to NO in the DemoApp, so the previews are removed without it being enabled.