Xcode 11 beta swift ui preview not showing : <p>Just playing with Swift UI basic app and the preview canvas is not showing even though I'm in canvas mode. App runs, and I have this little snippet what am I missing?</p>

<pre><code>#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
       ContentView()
    }
}
#endif
</code></pre>
