What is Clean Architecture in iOS?

A signature proves who sent a payload but says nothing about when, so an attacker who captures a valid signed request can resend it verbatim and it will still verify.
Clean Architecture organises code into concentric layers where dependencies only point inward.
Timer and CADisplayLink cause memory leaks because the target-action API causes the active RunLoop to retain the timer, and the timer retains its target object until explicitly invalidated.
MVVM (Model-View-ViewModel) separates business logic from UI.

Answer: Clean Architecture organises code into concentric layers where dependencies only point inward. The inner layers have no knowledge of the outer layers.

[ UI / Presentation ]
       ↓
[ Use Cases / Interactors ]
       ↓
[ Domain / Entities ]
       ↑
[ Data / Repositories ]  (implements interfaces defined in Domain)

Key rule: The Domain layer has zero imports of UIKit, SwiftUI, or any framework.

Code Example:

// Domain — pure Swift, no framework imports
struct Article { let id: String; let title: String }

protocol ArticleRepository {
    func fetchAll() async throws -> [Article]
}

class FetchArticlesUseCase {
    private let repo: ArticleRepository
    init(repo: ArticleRepository) { self.repo = repo }
    func execute() async throws -> [Article] { try await repo.fetchAll() }
}

// Data layer — implements the protocol
class RemoteArticleRepository: ArticleRepository { ... }

// Presentation layer — uses the use case
class ArticleViewModel: ObservableObject {
    private let useCase: FetchArticlesUseCase
    @Published var articles: [Article] = []
    func load() async { articles = try await useCase.execute() }
}