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Hammed Abass
fd4fff2c86
Added a comprehensive collection of Compose development guidelines, best practices, and skill definitions in the .codex directory. Co-authored-by: Junie <junie@jetbrains.com>
83 lines
4.0 KiB
Markdown
83 lines
4.0 KiB
Markdown
# Dependency Injection in Compose Projects
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Shared DI guidance for Jetpack Compose and Compose Multiplatform. For framework-specific setup, see [Koin](koin.md) or [Hilt](hilt.md).
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References:
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- [Koin](koin.md) — Koin setup, modules, Nav 3 integration, scopes, testing
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- [Hilt](hilt.md) — Hilt setup, modules, scopes, instrumented testing
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## When to Use Hilt vs Koin
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| Criterion | Hilt | Koin |
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| Platform | Android-only | Multiplatform (Android, iOS, Desktop, Web) |
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| Dependency resolution | Compile-time | Runtime (DSL) or compile-time (Koin Annotations + KSP) |
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| Error detection | Build-time | Runtime — use `verify()` in tests; KSP annotations add compile-time checks |
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| Setup complexity | Higher (Gradle plugins, annotations) | Lower (DSL modules); annotations optional |
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| Compose Multiplatform | Not supported | Full support |
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| Navigation 3 | `hiltViewModel()` in `entry<T>` blocks; multibinding entry providers — see [navigation-3-di.md](navigation-3-di.md) | `navigation<T>` DSL + `koinEntryProvider()` — see [navigation-3-di.md](navigation-3-di.md) |
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| Navigation 2 | `hiltViewModel()` in composable destinations; graph-scoped VMs — see [navigation-2-di.md](navigation-2-di.md) | `koinViewModel()`, `koinNavViewModel()`, `sharedKoinViewModel()` — see [navigation-2-di.md](navigation-2-di.md) |
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**Default recommendation:**
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- **Android-only projects**: Hilt is the default recommendation. Koin is also valid if the team prefers it or the project may become multiplatform later.
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- **Compose Multiplatform projects**: Use Koin — Hilt does not support non-Android targets.
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For detailed setup, modules, scoping, and testing, see the dedicated references: [koin.md](koin.md) and [hilt.md](hilt.md). This file stays focused on the framework decision — do not duplicate implementation details here.
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## Shared DI Concepts
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These principles apply regardless of framework choice:
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### Constructor injection as the default
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Always inject dependencies through the constructor. Field injection (`@Inject lateinit var`) couples the class to the DI framework and makes testing harder.
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### Interface-based design
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Bind interfaces to implementations — repositories, data sources, and platform services should be defined as interfaces. This enables swapping implementations in tests without mocking the DI framework.
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```kotlin
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// Define interface
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interface UserRepository {
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suspend fun getUser(id: String): User
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}
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// Bind implementation via DI
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// Koin: single<UserRepository> { UserRepositoryImpl(get()) }
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// Hilt: @Binds abstract fun bind(impl: UserRepositoryImpl): UserRepository
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```
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### Scope lifecycle alignment
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| Scope | When to use | Examples |
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| Singleton | Lives for app lifetime | API client, database, analytics |
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| Activity-retained | Survives config changes | User session, auth state |
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| ViewModel-scoped | Tied to a feature screen | Feature-specific calculators, validators |
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| Factory (new each time) | Stateless or short-lived | Formatters, mappers |
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Over-scoping wastes memory; under-scoping creates redundant instances. Match the scope to the dependency's actual lifetime.
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### Module organization
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Organize DI modules by feature, not by type. Each feature module declares its own dependencies:
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```text
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feature-product/
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ProductModule → repository, calculator, validator, ViewModel
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feature-settings/
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SettingsModule → repository, ViewModel
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core/
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CoreModule → API client, database, platform bindings
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```
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Combine feature modules in the app module. Platform-specific bindings go in platform modules (`androidMain`, `iosMain`).
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### Testing principle
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Swap real implementations with fakes via DI configuration — don't mock the DI framework itself. Both Koin and Hilt support module replacement in tests:
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- **Koin**: `appModule.verify()` for graph verification, module overrides in tests
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- **Hilt**: `@TestInstallIn` to replace modules, `hilt-android-testing` for instrumented tests
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For ViewModel unit testing (framework-agnostic), see [testing.md](testing.md).
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