Can you explain how the Dependency Injection library Koin works in Android applications?

Koin is a library for Dependency Injection (DI) in Android using Kotlin, which simplifies dependency management without the use of complex frameworks.

The main principle of Koin:

1. Defining modules — dependencies that Koin will provide are described.
2. Starting Koin — initializing the DI container in the application.
3. Injecting dependencies — obtaining the required objects through Koin.

Example:

// Define a module with dependencies
val appModule = module {
    single { Repository() } // singleton
    factory { ViewModel(get()) } // a new instance each time, gets Repository
}

// In the Application class
class MyApp : Application() {
    override fun onCreate() {
        super.onCreate()
        startKoin {
            androidContext(this@MyApp)
            modules(appModule)
        }
    }
}

// In Activity or Fragment
class MyActivity : AppCompatActivity() {
    private val viewModel: ViewModel by inject()
}

Thus, Koin automatically creates and passes the required objects, making testing and maintaining the code easier.