I have a sample SwiftUI iOS app. As shown in the screenshot below, my project has three configurations: Debug, MyDebug, Release.
If I select the Debug or MyDebug scheme, I get a preview. But if I select the Release scheme, I get an error that says the following.
”***.app” needs -Onone Swift optimization level to use previews (current setting is -O)
, where *** is the app name.
It probably has nothing to do with the Preview error, but the Info.plist has a dictionary such that the key name is devMode, and the value is $(DEVMODE). And I have a user-defined setting as shown below.
My ContentView has the following.
import SwiftUI
struct ContentView: View {
@State private var state: String = ""
var body: some View {
VStack {
Text("Hello, world!: \(state)")
}
.onAppear {
if let devMode = Bundle.main.object(forInfoDictionaryKey: "devMode") as? String {
print("Development mode: \(devMode)")
state = devMode
}
if let path = Bundle.main.path(forResource: "Info", ofType: "plist") {
if let dict = NSDictionary(contentsOfFile: path) {
print("**** \(dict)")
}
}
#if DEBUG
print("Debug")
#elseif MYDEBUG
print("MyDebug")
#else
print("Que?")
#endif
}
}
}
#Preview {
ContentView()
}
So my question is how I get the preview for all three build schemes? Muchos thankos.
Hi @Tomato,
This error is informing you that Previews cannot work with optimizations turned on. Release build uses -0 in the Swift compiler and other optimizations, like dead code stripping, in the linker. These are incompatible while running under Previews. You can only preview in a configuration like Debug that does not optimize the build.
Cheers,
Paris X Pinkney | WWDR | DTS Engineer
