Challenge: View Reuse |

This is a companion discussion topic for the original entry at

Hey Jessy,

After doing this challenge I’ve ended up refactoring the Book view to a reusable component so it allows me to show a book for both the list view and the detailed view using a single component. This is what I came up with:
Screen Shot 2020-11-24 at 09.11.48

However, there’s an error in the code that tells me that the asPreview property is being used before initialization inside the initializer function itself and that is a little confusing. I’m sure that if I just remove the initializer function it should work, but I want to know if it’s possible to use default parameters in this case.


The error is incorrect; the compiler doesn’t know how to properly deal with you attempting to assign a UIImage? to what is actually a State<UIImage?>.

To do that, you need to choose one of these options:

  1. Change your line to this:
_image = .init(initialValue: image)
  1. Move the line to the end of the initializer. That will generate the equivalent of the following, for you, which you can then overwrite:
_image = .init(initialValue: nil)

As for why the second option works, it looks like a property wrapper-related compiler bug to me, and I recommend sending it over to

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All right, no problem, here’s the ticket if you want to check it out: [SR-13896] Confusing error message when assigning an optional UIImage as a state property · Issue #57 · apple/swift-xcode-playground-support · GitHub

Initializing using _image did the trick! Thanks!

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Hey, I’m having a weird issue - as far as I can tell the detail view displays correctly, but the spacer I put in the VStack doesn’t seem to have an effect when I look at the detail in the live preview. Here’s what it looks like in the DetailView Preview: image

And here’s the live preview, after navigating from the list view:image

You can see it’s centered on the screen here, where the one above has it at the top, where it should be.

This is super super minor, but at 3:50 you say you changed the alignment to leading using “Command, Control, Click”, but I believe the shortcut is “Control, Option, Click”