How does _AppStorage interoperate with SwiftUI AppStorage?

[Zeta611]

The following does not properly inject values:

withDependencies {
  $0.userDefaults = .ephemeral()
  $0.userDefaults.set("hello", forKey: "myKey")
} operation: {
  MyView()
  }

where MyView has

@AppStorage("myKey") var myKey = "init"

It works when I replace @AppStorage("myKey") with @Dependency.AppStorage("myKey") though.

However, README says that they should interoperate when they have the same keys, and yet it doesn't seem to work the way I expected.
How are they supposed to interoperate?

Thank you!

[tgrapperon]

Hey @Zeta611! Sorry if this wasn't clear: they interoperate only with the default live implementation. In your case, you're using the ephemeral storage, but the SwiftUI variant doesn't know anything about that. They interoperate when you don't override userDefault storage (or use the same UserDefaults instance), because they're writing to the same place, in the same fashion, and they both observe changes to this storage. It means that you can create a Settings model that writes to @Dependency.AppStorage, and pop this preference in any View elsewhere in the hierarchy using SwiftUI's @AppStorage for example.

It is partly working here because you defined your View in a withDependency block, but @Dependency.AppStorage will not invalidate the view if its value change. In a general manner, I wouldn't use @Dependency stuff in view, excepted very locally for previews (but as I said earlier, ephemeral() app storage wouldn't interoperate with SwiftUI's AppStorage).

I'll think about rephrasing this to make it clearer. I'll also think if I could make ephemeral work in a View, but I'm not sure this is possible.

[Zeta611]

Thank you for the clarification!
I have one more follow up question to clarify: If I don't explicitly set $0.userDefaults = .liveValue, @Dependency.AppStorage does not interoperate with @AppStorage in a preview. So is .previewValue used automatically in the context of a PreviewProvider?

[tgrapperon]

Yes previewValue is automatically used in a PreviewProvider, that's its main feature.
As previews are considered discardable, I've opted to default userDefault to ephemeral for them, so you always know how with what you're starting with. I may add an additional closure that would allow to define initial values though.

[Zeta611]

Thank you very much for the prompt reply!