Leverage Dependency Injection as an Android Developer

🔹 Introduction

As your mobile application grows, managing dependencies becomes essential. Good architecture isn't just about writing working code — it's about writing modular, testable, and maintainable code.
That’s where Dependency Injection (DI) comes in.

🔹 What is Dependency Injection?

Dependency Injection is a design principle where a class receives its dependencies from the outside instead of creating them internally.

🔧 A dependency is any other class a component needs to function (e.g. UserRepository inside UserViewModel).

❌ Bad practice: direct instantiation

class UserViewModel {
    val repository = UserRepository() // Strong coupling
}

✅ Good practice: constructor injection

class UserViewModel(private val repository: UserRepository)

This allows better separation of concerns and testability.

🔹 Benefits of Dependency Injection

• ✅ Decouples components

• ✅ Reusability across contexts

• ✅ Easy unit testing with mock injections

• ✅ Flexibility for switching implementations

🔹 Manual DI in Android with Kotlin

💡 Simple manual injection

class UserRepository
class UserViewModel(private val repository: UserRepository)

fun main() {
    val repo = UserRepository()
    val viewModel = UserViewModel(repo)
}

Works for small apps — but becomes a mess in real-world, large-scale applications.

🔹 Limitations of manual DI

• ❌ Repetitive and boilerplate-heavy

• ❌ No lifecycle awareness (e.g. ViewModel vs singleton)

• ❌ Not scalable

• ❌ Harder to maintain and test in big teams

🔹 Overcome limitations with Koin or Dagger Hilt

✅ With Koin (Kotlin-first, lightweight)

val appModule = module {
    single { UserRepository() }
    viewModel { UserViewModel(get()) }
}

✅ With Dagger Hilt

@Module
@InstallIn(SingletonComponent::class)
object AppModule {
    @Provides fun provideRepository() = UserRepository()
}

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
    @Inject lateinit var viewModel: UserViewModel
}

🔹 Conclusion

Dependency Injection isn’t just “clean code.” It’s a must-have practice for building modular, testable, and maintainable Android apps.
With tools like Koin or Hilt, it becomes easier than ever to adopt DI in your architecture — no excuses!

If you want to build solid, scalable Android apps, DI is the way to go.