Apple has officially released macOS Catalina. It’s time to upgrade if you want to fully explore SwiftUI. Without upgrading to the latest version of macOS, even if you’re using Xcode 11, you won’t be able to use the instant preview when developing with the SwiftUI framework.
Thanks for your interest in our upcoming book on SwiftUI. We’re hard at work writing the book and re-testing all demo code. It should be ready before end Oct. You will receive an update on that later this month.