🧑🏻‍💻 When a Module Is Not Required: Concrete Classes

In Hilt/Dagger, concrete classes with an @Inject constructor can be injected automatically.

class ApiClient @Inject constructor()

class UserRepository @Inject constructor(
    private val api: ApiClient
)

Point:
If the class can be instantiated directly, a Module is not required.

 

🧑🏻‍💻 When a Module Is Required (1): Interfaces

When injecting an interface, Hilt cannot determine which implementation to use.

You need to specify it explicitly using @Binds inside a Module.

interface Logger { 
    fun log(msg: String) 
}

class ConsoleLogger @Inject constructor() : Logger

@Module
@InstallIn(SingletonComponent::class)
interface LoggerModule {
    @Binds
    fun bindLogger(impl: ConsoleLogger): Logger
}

Point:
Interfaces always require a Module.

 

🧑🏻‍💻 When a Module Is Required (2): External Libraries

External libraries typically do not have @Inject constructor.

You must provide the creation logic inside a Module.

@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {
    @Provides
    fun provideClient(): OkHttpClient = OkHttpClient.Builder().build()
}

Point:
You make external classes injectable by defining how to create them in a Module.

 

🧑🏻‍💻 Summary

• Your own concrete classes → auto-injectable
• Interfaces & external libraries → Module required
• Multiple implementations or singleton handling → use @Qualifier, @Named, @Singleton

👉 Dagger/HiltでModuleが必要か一目でわかるようにパターン化する

Related Categories :  Android・Developmemt・Recommended