Android

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

Get the code

Gradle Setup

Add the Koin Android dependency like below:

// Add Jcenter to your repositories if needed
repositories {
jcenter()
}
dependencies {
// Koin for Android
compile "org.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 presenter class, for consuming this data:

class MySimplePresenter(val repo: HelloRepository) {
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() }
// Simple Presenter Factory
factory { MySimplePresenter(get()) }
}

?> we declare our MySimplePresenter class as factory to have a create a new instance each time our Activity will need one.

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

class MySimpleActivity : AppCompatActivity() {
// Lazy injected MySimplePresenter
val firstPresenter: MySimplePresenter by inject()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
//...
}
}
info

The by inject() function allows us to retrieve Koin instances, in Android components runtime (Activity, fragment, Service...)

info

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