Android Koin Get Started

What is Koin?

Koin is simple dependency injection support using DSL by Kotlin. (A programatic lightweight dependency injection framework)

These days, DI is popular in Android, (Dagger2 etc..) Koin is simple and easy to use

What to cover in this sample

• General Inject
• View Model Inject

Preparation

To use Koin, we need to add gradle description (Use version 2.1.3)

implementation 'org.koin:koin-android:2.1.3'
// Koin Android Scope feature
implementation "org.koin:koin-android-scope:2.1.3"
// Koin Android ViewModel feature
implementation "org.koin:koin-android-viewmodel:2.1.3"

Scope is not required in this sample. ViewModel is for ViewModel injection

Let’s start sample

General Inject

The first is simple example.

Prepare following codes

• HelloRepository
• HelloRepositoryImpl
• HelloSimplePresenter
• modules.kt
• MyApplication
• MainActivity
• AndroidManifest.xml

HelloRepository.kt

interface HelloContextRepository {
    fun getName() : String
}

HelloRepositoryImpl.kt

This is implementation of above interface

class HelloRepositoryImpl() : HelloRepository {
    override fun giveHello() = "Hello Koin"
}

HelloSimplePresenter

This is factory class

class HelloSimplePresenter(val repo: HelloRepository) {

    fun sayHello() = "${repo.giveHello()} from $this"
}

modules.kt

Prepare module import to use

import org.koin.android.ext.koin.androidContext
import org.koin.android.viewmodel.dsl.viewModel
import org.koin.core.qualifier.named
import org.koin.dsl.module

val appModule = module {
    single<HelloRepository> { HelloRepositoryImpl() }

    factory { HelloSimplePresenter(get()) }

    // This is for next ViewModel inject
    single<HelloViewModelRepository> { HelloViewModelRepositoryImpl()}
    viewModel { HelloViewModel(get()) }
}

MyApplication

Use startKoin to import module list and some setup (context, logger etc…, Only modules are required, others are not mandatory)

class MyApplication : Application() {

    override fun onCreate() {
        super.onCreate()

        // Start Koin
        startKoin {
            // use AndroidLogger as Koin Logger - default Level.INFO
            // The androidLogger() function makes it possible to receive logs from Koin
            androidLogger()

            // use the Android context given there
            androidContext(this@MyApplication)

            // load properties from assets/koin.properties file
            androidFileProperties()

            modules(appModule)
        }
    }
}

MainActivity

Test to use (both general and view model)

class MainActivity : AppCompatActivity() {

    val firstPresenter: HelloSimplePresenter by inject()

    val myViewModel: HelloViewModel by viewModel()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val greeting = firstPresenter.sayHello()
        print(greeting)
        // Hello Koin from
        val presenter : HelloSimplePresenter = get()
        val greetintg2 = presenter.sayHello()
        print(greetintg2)
        // Hello Koin from
        val greeting3 = myViewModel.sayHello()
        // Hello ViewModel Koin from 
        print(greeting3)
    }
}

View Model Inject

• HelloViewModel
• HelloViewModelRepository
• HelloViewModelRepositoryImpl

HelloViewModel

class HelloViewModel(val repo: HelloViewModelRepository) : ViewModel() {

    fun sayHello() = "${repo.giveHello()} from $this"
}

HelloViewModelRepository

interface HelloViewModelRepository {
    fun giveHello(): String
}

HelloViewModelRepositoryImpl

class HelloViewModelRepositoryImpl() : HelloViewModelRepository {

    override fun giveHello()= "Hello ViewModel Koin"
}

ViewModel and general inject is almost all same