iOS Dependency Injection Standards

Priority: P0

Implementation Guidelines

Protocol-Based DI (Manual)

• Initializer Injection: Preferred method. Pass dependencies through init.
• Abstractions: Inject protocols instead of concrete classes to facilitate testing (Mocks/Stubs).

Modern Property Wrappers (Factory/Resolver)

• Factory: Use the Factory library for lightweight, type-safe navigation-friendly DI.
• Swinject: Use for enterprise-grade container-based DI in large modular projects.
• Injected: Use @Injected property wrappers for cleaner syntax in ViewModels.

Scoping

• Singleton: Use for app-wide services (Auth, Network, Database).
• Unique/Transient: Default for ViewModels and temporary workers.
• Graph/Cached: Use for shared data within a specific feature flow (Coordinator scope).

Anti-Patterns

• Singletitis: **No global Shared singleton access everywhere**: Inject the service via initializer.
• Service Locator: **No Resolver.resolve() inside logic**: Pass dependency via constructor or property wrapper.
• Concrete Dependency: **No direct class instantiation**: Depend on protocols for testability.

References

• Manual & Library DI Setup