DI with Koin - Introduction and Implementation

 What is Koin ?

It is a smart Kotlin Dependency Injection Library. 

Its features are: 

• Light weight 
• Easy to learn 

Terminology: 

• module - it creates a module in Koin which would be used by Koin to provide all the dependencies.
• single - it creates a singleton that can be used across the app as a singular instance.
• factory - it provides a bean definition, which will create a new instance each time it is injected.
• get() - it is used in the constructor of a class to provide the required dependency.

Implementation:

Gradle Setup: 

// koin
// Koin main features for Android (Scope,ViewModel ...)
implementation "io.insert-koin:koin-android:${koin_version}"
// Koin Android - experimental builder extensions
implementation "io.insert-koin:koin-android-ext:${koin_version}"
// Koin for Jetpack WorkManager
implementation "io.insert-koin:koin-androidx-workmanager:${koin_version}"

// Current version
koin_version= "3.0.1-beta-2"

Create Your Components: 

Service 

interface KoinService {
    fun provideService(): String
}

Repository 

class KoinRepository : KoinService {
    override fun provideService(): String = "Provide Koin Service 1"
}

ViewModel 

class KoinViewModel(val repo: KoinRepository) : ViewModel(){
    fun doSomethingWithService() = repo.provideService()
}

Declare the Koin Module: 

val appModule = module {

    // single instance of KoinRepository
    single<KoinService> { KoinRepository() }

    // KoinViewModel
    viewModel { KoinViewModel(get()) }
}

Start Koin From your Application Class: 

class MyApp : Application() {


    override fun onCreate() {
        super.onCreate()

        startKoin {
            androidLogger()
            androidContext(this@NotifyMeApp)
            modules(appModule)
        }
    }

}

Finally you can Inject the Dependency and use it: 

class KoinActivity : AppCompatActivity() {

    //lazy inject viewmodel
    val myViewModel: KoinViewModel by viewModel()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_first)
        // use your viewmodel here
        myViewModel.doSomethingWithService()
    }
}

N.K.