问题
I build an app with the 2nd beta of Xcode 11, using SwiftUI, and everything worked completely fine, but now, with the 3rd beta, the app isn't even build. I get errors like "Use of undeclared type 'View'", "Unknown attribute 'State'" etc. What can I do? Is the problem in my code or is it just a bug?
The problem is when I'm trying to build the app to run on my Mac (with UIKit for Mac)
@State var score = 0
The error is "Unknown attribute 'State'"
struct ContentView : View {
/*...*/
}
The error is "Use of undeclared type 'View'"
回答1:
This is from the Xcode 11 Beta 3 Release Notes.
Known Issues
- Xcode 11 doesn’t support working with SwiftUI in an iPad app brought to macOS. (41416222, 51201699)
I downloaded the Xcode 11 Beta 3 myself just to confirm the errors you mentioned, and I had the same issues when trying to build a SwiftUI project for Mac.
I would suggest going back to using Xcode Beta 2 if possible. Unfortunately, Apple doesn't provide download links to previous betas, so hopefully you have a Time Machine backup or Beta 2 still installed on your computer. Otherwise, you might be out of luck until the next beta is released.
回答2:
I was getting the same "Unknown attribute 'State'" issue in Beta 5. But I was doing "@state" and not "@State". Case matters. It's hard to notice because both ways are shown as purple.
回答3:
Got same issue on Xcode 11.2. Found out that the reason was that somewhere in same module I declared protocol State {}. This breaks compiler without any reasonable errors.
来源：https://stackoverflow.com/questions/56967198/xcode-11-beta-3-build-error-unknown-attribute-state-use-of-undeclared-typ