title: Xcode Canvas for SwiftUI previews does not show up
body: <p>I´m trying to get the new Canvas feature from Xcode 11 running, but the Canvas won´t show up. What am I doing wrong?</p>
  <p>This new Xcode feature should show a live preview of my SwiftUI views without running the app.</p>
  <blockquote>
  <p>When you create a custom View with SwiftUI, Xcode can display a preview of the view’s content that stays up to date as you make changes to the view’s code. You define a structure that conforms to the PreviewProvider protocol to tell Xcode what to display. Xcode shows the preview in a canvas beside your code.</p>
  <p><a href="https://developer.apple.com/documentation/swiftui/previews-in-xcode" rel="nofollow noreferrer">https://developer.apple.com/documentation/swiftui/previews-in-xcode</a></p>
  </blockquote>
  <p>I just created a new default project (single view app), compiled it and activated 'Editor &gt; Editor and Canvas'. I can navigate to each file in the project, nothing shows up.</p>
  <p>What else does need to be done?</p>