android-dependency-injection

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name: android-dependency-injection description: Dependency injection with Hilt/Dagger — setup, scoping, multi-module, testing. user-invocable: true

Android Dependency Injection

Cross-cutting skill — always activates alongside the project-type-specific skill.

Hard Rules

• Use Hilt as the default DI framework for Android projects.
• Annotate Application class with @HiltAndroidApp.
• Annotate all Activities and Fragments that use injection with @AndroidEntryPoint.
• Scope dependencies correctly — @Singleton for app-wide, @ViewModelScoped for ViewModel lifetime.
• Never inject Activity or Fragment context into @Singleton-scoped objects — use @ApplicationContext.
• Define bindings in @Module classes — use @Binds for interface-to-implementation, @Provides for construction.
• Use @Qualifier annotations to distinguish same-type bindings — not named strings.
• Keep modules focused — one module per feature boundary.
• Use constructor injection over field injection wherever possible.
• Never use Dagger directly when Hilt is available — Hilt reduces boilerplate.

Core Patterns

• @InstallIn(SingletonComponent::class) for app-wide singletons.
• @InstallIn(ViewModelComponent::class) for ViewModel-scoped dependencies.
• Use @AssistedInject for WorkManager Workers and other assisted construction.
• Define interface in feature-api, implementation binding in feature-impl module.
• Use @EntryPoint for injecting into classes Hilt doesn't manage (ContentProvider, etc.).
• Wrap third-party SDK initialization in @Provides methods for testability.

References

• references/hilt_setup.md
• references/scoping.md
• references/multi_module_di.md
• references/testing_di.md
• references/common_mistakes.md
• references/advanced_patterns.md