Android ViewModel

This tutorial lets you write an Android/Kotlin application and use Koin inject and retrieve your ViewModel components.

Get the code

info

The source code is available at on Github

Gradle Setup

Add the Koin Android dependency like below:

// Add Maven Central to your repositories if needed

repositories {

mavenCentral()

}

dependencies {

// Koin for Android

implementation "io.insert-koin:koin-android:$koin_version"

}

Our components

Let's create a HelloRepository to provide some data:

interface HelloRepository {

fun giveHello(): String

}

class HelloRepositoryImpl() : HelloRepository {

override fun giveHello() = "Hello Koin"

}

Let's create a ViewModel class, for consuming this data:

class MyViewModel(val repo : HelloRepository) : ViewModel() {

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

}

Writing the Koin module

Use the module function to declare a module. Let's declare our first component:

val appModule = module {

// single instance of HelloRepository

single<HelloRepository> { HelloRepositoryImpl() }

// MyViewModel ViewModel

viewModel { MyViewModel(get()) }

}

info

we declare our MyViewModel class as a viewModel in a module. Koin will give a MyViewModel to the lifecycle ViewModelFactory and help bind it to the current component.

Start Koin

Now that we have a module, let's start it with Koin. Open your application class, or make one (don't forget to declare it in your manifest.xml). Just call the startKoin() function:

class MyApplication : Application(){

override fun onCreate() {

super.onCreate()

// Start Koin

startKoin{

androidLogger()

androidContext(this@MyApplication)

modules(appModule)

}

}

}

Injecting dependencies

The MyViewModel component will be created with HelloRepository instance. To get it into our Activity, let's inject it with the by viewModel() delegate injector:

class MyViewModelActivity : AppCompatActivity() {

// Lazy Inject ViewModel

val myViewModel: MyViewModel by viewModel()

override fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState)

setContentView(R.layout.activity_simple)

//...

}

}

info

The by viewModel() function allows us to retrieve a ViewModel instance from Koin, linked to the Android ViewModelFactory.

The getViewModel() function is here to retrieve directly an instance (non lazy)