Microapps Architecture: Resources and Localization (Swift)

Part three of the microapps series moves resources and translations into the modules that use them. The compiler generates a bundle per module with resources, reachable as Bundle.module, and forgetting the bundle parameter is the classic missing-image bug.

Module Bundles

Image("image") looks in the running target's bundle, so a resource that lives in a package module needs .module spelled out. Xcode auto-bundles asset catalogs, Core Data models, Storyboards, NIBs, and localization files; Bundle.module exists only for modules that contain resources. Wrap the lookup in a type-safe factory so feature modules cannot mistype names:

// DesignSystem module
extension UIImage {
  public enum Icon: String {
    case trash
    case star
    case plus
  }

  public static func get(_ icon: Icon) -> UIImage {
    .init(named: icon.rawValue, in: .module, compatibleWith: .current)!
  }
}

Other file types must be declared in Package.swift. process lets Xcode apply platform-specific compression; copy keeps files and sub-directory structure verbatim.

.target(
  name: "DesignSystem",
  resources: [
    .copy("Resources/Fonts"),
    .process("Resources/PNGs")
  ]
)

Localization per Feature Module

Each feature module carries its own Localizable.strings, so it can build and run as a standalone microapp. Set defaultLocalization: "en" on the package, add en.lproj and other <locale>.lproj folders inside the module, and always pass the bundle when reading a string:

Text("helloMessage", bundle: .module)

A shared view that displays localized text from other modules must accept the bundle in its public initializer, because otherwise it can only see its own strings:

// DesignSystem module
public struct PlaceholderView: View {
  let text: LocalizedStringKey
  let bundle: Bundle?
  let systemImage: String

  public init(_ text: LocalizedStringKey, bundle: Bundle? = nil, systemImage: String) {
    self.text = text
    self.bundle = bundle
    self.systemImage = systemImage
  }

  public var body: some View {
    Label {
      Text(text, bundle: bundle)
    } icon: {
      Image(systemName: systemImage)
    }
  }
}

// Search feature module
PlaceholderView("emptySearchPlaceholder", bundle: .module, systemImage: "magnifyingglass")

Two rules keep the separation clean: a resource lives only in the module that uses it, and shared resources get a type-safe public API.