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mastering_xcode_previews.md

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WWDC19

Table of Contents

=================

Mastering Xcode Previews - Thursday

Session materials: https://developer.apple.com/videos/play/wwdc2019/233/

  • Xcode builds a preview of the current view separately and injects the view with dynamic replacement to show in the preview mode

PreviewProvider Protocol

# if DEBUG
public enum SomePreviews: PreviewProvider {
  public static var previews: some View {
    Group {
      SomeView()
      .device() // Different devices to be shown in the preview
      .previewLayout(.sizeThatFits) // Just shows the specific view with the intrinsic size it gets,

      SomeView()
      .environment(|.sizeCategory, .extraLarge) // To simulate dynamic text sizes on the preview
      .previewDisplayName() // to show the selected preview option in the preview mode
    }
  }
}
#endif
  • Wrap previewable views into forEach to simulate different cases of an iterable like dynamic font types

Development Assets

  • Target settings -> General -> Development Assets

Populate The Preview with Fixtures (JSON)

  • Parse a given JSON with a simple decoder to have a variety of data to be able to check different cases on the preview UI

  • Pinning a preview will make it sticky across other views to make it visible everywhere

Create a New Preview File for an Existing View Controller

  • A separate previews file
// Implement following two protocols to make the vc previewable
PreviewProvider
static var previews

UIViewControllerRepresentable
func makeUIViewController() {
  // load from storyboard or instantiate
}

func updateUIViewController() {}
  • Make your apps scene aware

Image