Koin vs Dagger 2 vs Hilt: Which one should we use? ☕

Have you ever heard about Dependency Injection? If you haven't heard it before, let’s break down Dependency Injection (DI) in the simplest way possible.

Imagine you’re building a coffee machine. Instead of the machine creating its own coffee beans and water, you provide them from the outside. This way, you can easily swap out different types of beans or water sources without rebuilding the entire machine.

In coding, Dependency Injection (DI) works the same way. Instead of a class creating its own dependencies, they’re injected from the outside. This makes your code more flexible, testable, and easier to manage. Android frameworks like Dagger 2, Hilt, and Koin help automate this process, so you don’t have to manually pass everything around.

These three are popular DI frameworks used in Android development. They help manage object creation and dependency resolution, making code cleaner, more modular, and easier to maintain. Let's deep dive into among of these three and compare them by performance, usability, and community support.

Performance
When comparing Koin, Dagger 2, and Hilt for dependency injection in Android development, performance plays a crucial role. Dagger 2 is a compile-time dependency injection framework, meaning it generates code at build time, leading to optimal runtime performance with minimal overhead. Hilt, built on top of Dagger 2, maintains the same compile-time benefits while simplifying its setup. Koin, on the other hand, is a runtime dependency injection framework that uses reflection and service locators, making it slightly slower than Dagger 2 and Hilt, especially in large-scale applications. While the difference may not be significant for smaller apps, it can impact performance in more complex dependency graphs.

Let say we demonstrate a "hello world" app using among of them and this is the result:

from the illustration above we can conclude:

• Koin: Koin's compile-time is the fastest because it primarily relies on Kotlin's reflection and doesn't involve extensive code generation.

• Dagger 2: Dagger 2's compile-time is significantly longer due to the code generation process, even for a simple app.

• Hilt: Hilt, being built on Dagger 2, also involves code generation, but it's often more optimized for Android and might have slightly faster compile times than raw Dagger 2 in a very small project.

Usability
In terms of usability, Koin is the easiest to implement, requiring minimal boilerplate code with a simple DSL for defining dependencies. Dagger 2 is more complex due to its annotation-based approach, requiring knowledge of components, modules, and generated code. Hilt simplifies Dagger 2’s complexity by introducing annotations like @HiltAndroidApp and @Inject, making dependency injection easier to manage while still leveraging compile-time validation.

Community Support and Documentation
Regarding community support and documentation, Dagger 2 has been widely adopted in the Android ecosystem for years and has extensive documentation. Hilt, as an official AndroidX library, benefits from strong Google backing and comprehensive guides. Koin, while popular among Kotlin developers, has a smaller but growing community. Its documentation is clear but not as extensive as Google's offerings. Ultimately, Dagger 2 and Hilt are preferred for performance-sensitive and large-scale projects, while Koin is an excellent choice for developers seeking simplicity and faster integration.

Below are example implementations of Koin, Dagger 2, and Hilt:

Koin Implementation

// Define a module
val appModule = module {
    single { UserRepository() }
}

// Start Koin
class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        startKoin {
            modules(appModule)
        }
    }
}

// Inject dependency
class MyViewModel(private val repository: UserRepository)

Dagger 2 Implementation

// Define a module
@Module
class AppModule {
    @Provides
    fun provideUserRepository(): UserRepository {
        return UserRepository()
    }
}

// Define a component
@Component(modules = [AppModule::class])
interface AppComponent {
    fun inject(activity: MainActivity)
}

// Inject dependency
class MainActivity : AppCompatActivity() {
    @Inject lateinit var repository: UserRepository
}

Hilt Implementation

// Define a module
@InstallIn(SingletonComponent::class)
@Module
object AppModule {
    @Provides
    fun provideUserRepository(): UserRepository {
        return UserRepository()
    }
}

// Inject dependency
@HiltAndroidApp
class MyApplication : Application()

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
    @Inject lateinit var repository: UserRepository
}

Choose wisely what framework you want to use, these trio have pros and cons. You can choose and implement it based on your need. Happy coding :)

Documentation:
Dagger 2
Hilt
Koin