Getting started with Android Architetcure & ViewModel

Let’s start with Koin on a Android app with ViewModel feature

About

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

Get the code

Checkout the project directly on Github or download the zip file

Gradle Setup

Add the Koin Android dependency like below:

// Add Jcenter to your repositories if needed
repositories {
    jcenter()    
}
dependencies {
    // Koin for Android - Scope feature
    // include koin-android-scope & koin-android
    compile 'org.koin:koin-android-viewmodel:1.0.2'
}

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()) }
}

Note: 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(this, listOf(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)

        //...
    }
}

What’s Next?

You have finished this starting tutorial. Below are some topics for further reading:

Also other Android getting started project: