hilt-di

Hilt Dependency Injection

10 rules that fix what AI agents consistently get wrong with Hilt.

Setup — required before any injection works

// MyApplication.kt — REQUIRED, must be declared in AndroidManifest
@HiltAndroidApp
class MyApplication : Application()

// AndroidManifest.xml
<application android:name=".MyApplication" ...>

// build.gradle.kts — use KSP, never kapt
plugins {
    alias(libs.plugins.ksp)
    alias(libs.plugins.hilt)
}
dependencies {
    implementation(libs.hilt.android)
    ksp(libs.hilt.compiler)                          // ← ksp, not kapt
    implementation(libs.androidx.hilt.navigation.compose)
}

Rule 1: @Binds over @Provides for interface binding

// ✅ @Binds — zero runtime overhead, compiler-verified
@Module
@InstallIn(SingletonComponent::class)
abstract class RepositoryModule {
    @Binds
    @Singleton
    abstract fun bindItemRepository(impl: ItemRepositoryImpl): ItemRepository

    @Binds
    @Singleton
    abstract fun bindUserRepository(impl: UserRepositoryImpl): UserRepository
}

// ❌ @Provides for interface — works but is less efficient
@Module
@InstallIn(SingletonComponent::class)
object RepositoryModule {
    @Provides
    @Singleton
    fun provideItemRepository(impl: ItemRepositoryImpl): ItemRepository = impl
}

Rule 2: @Provides for third-party / constructed objects

// ✅ @Provides when you control construction
@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {
    @Provides
    @Singleton
    fun provideOkHttpClient(): OkHttpClient =
        OkHttpClient.Builder()
            .addInterceptor(HttpLoggingInterceptor().apply { level = Level.BODY })
            .connectTimeout(30, TimeUnit.SECONDS)
            .build()

    @Provides
    @Singleton
    fun provideRetrofit(okHttpClient: OkHttpClient): Retrofit =
        Retrofit.Builder()
            .baseUrl(BuildConfig.BASE_URL)
            .client(okHttpClient)
            .addConverterFactory(Json.asConverterFactory("application/json".toMediaType()))
            .build()

    @Provides
    @Singleton
    fun provideItemApiService(retrofit: Retrofit): ItemApiService =
        retrofit.create(ItemApiService::class.java)
}