Container Views: Values (SwiftUI)

Container values pass data from a child view up to its custom container, the way environment values pass data down. The container reads them off each Subview or SectionConfiguration and changes its layout, so callers tag content instead of relying on positional order.

Define a value with @Entry

Extend ContainerValues with the @Entry macro and a default. Set it on any view or section with containerValue(_:_:), and wrap that in a View extension for a cleaner call site.

extension ContainerValues {
  @Entry var isFeatured = false
}

extension View {
  func featured(_ isFeatured: Bool = true) -> some View {
    containerValue(\.isFeatured, isFeatured)
  }
}

Tag content at the call site

Magazine {
  Section(header: Text("Favorites")) {
    Color.red
    Color.orange
  }

  Section {
    Color.green
    Color.yellow
  }
  .featured()
}

Without container values the container must hard-code positions, for example "the first section is prominent". The tag makes the choice explicit and order-independent.

Read values inside the container

Both Subview and SectionConfiguration expose containerValues. Filter on the value to recompose the hierarchy.

Group(sections: content) { sections in
  let featured = sections.filter(\.containerValues.isFeatured)
  ForEach(featured) { section in
    section.content.frame(minHeight: 100)
  }

  let rest = sections.filter { !$0.containerValues.isFeatured }
  ForEach(rest) { section in
    section.header
    // horizontal rail per section
    section.footer
  }
}

Container values propagate like environment values: every view inside a featured section reads isFeatured as true.