I can't build even a simple SwiftUI file in my project without running into an error in the Preview pane, which says "Cannot preview this file - not building -Onone".
When I tap the little info button, it shows me this message:
Can anyone help me figure this out? Thanks.
When I tap the little info button, it shows me this message:
This is with Xcode11.5. My project file has been around for quite a while, but I keep updating it frequently, so I'm not sure what setting I've missed. The code compiles file, but I can't see any live previews with SwiftUI.OptimizationLevelError: not building -Onone
"CJDashboard.app" needs -Onone Swift optimization level to use previews
Can anyone help me figure this out? Thanks.
This is driven by the "Optimization Level" setting in the build settings for the target that contains the file you're editing. One of two things is happening…
That value accidentally got set to something other than Onone for your debug build
The scheme you're using has a configuration set that isn't your debug one. By default, projects come with a "Debug" and "Release" config. The "Debug" config is configured to build Onone, which means without optimizations. And the "Release" config is configured to build with optimizations. You just need to double check the build configuration selected for your scheme is your debug (usually "Debug") one.
