WWDC19

Table of Contents

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

• Mastering Xcode Previews - Thursday
  • PreviewProvider Protocol
  • Development Assets

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