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Injecting in Jetpack Compose and Android

This page describe how you can inject your dependencies for your Jetpack Compose app - https://developer.android.com/jetpack/compose

Starting Koin with Android Jetpack Compose - KoinApplication or KoinAndroidContext (since 1.1.0)​

Most of the time, startKoin function is used to start Koin in your application. This is done before running any Composable function. You need to setup Compose with your current Koin instance. Use KoinAndroidContext() to do so:

@Composable
fun App() {
    // Set current Koin instance to Compose context
    KoinAndroidContext() {

        MyScreen()
    }
}

Else if you want to start a new Koin instance from your Compose app, The function KoinApplication helps to create Koin application instance, as a Composable. This is a replacement of the classic startKoin application function.

@Composable
fun App() {
    KoinApplication(application = {
        // Koin configuration here
    }) {
        
    }
}
info

Difference between KoinAndroidContext and KoinContext:

  • KoinAndroidContext is looking into current Android app context for Koin instance
  • KoinContext is looking into current GlobalContext for Koin instances

Compose Preview with Koin​

The KoinApplication function is also interesting to start dedicated context for preview. This can be also used to helo with Compose preview:

@Composable
@Preview
fun App() {
    KoinApplication(application = {
        // your preview config here
        modules(previewModule)
    }) {
        // Compose to preview with Koin
    }
}

Injecting into a @Composable​

While writing your composable function, you gain access to the following Koin API:

  • koinInject() - fetch instance from Koin container
  • getKoin() - get current Koin instance

For a module that declares a 'MyService' component:

val androidModule = module {

    single { MyService() }
}

We can get your instance like that:

@Composable
fun App() {
    val myService = koinInject<MyService>()
}
note

To keep aligned on the functional aspect of Jetpack Compose, the best writing approach is to inject instances directly into functions properties. This way allow to have default implementation with Koin, but keep open to inject instances how you want.

@Composable
fun App(myService: MyService = koinInject()) {
}

ViewModel for @Composable​

The same way you have access to classical single/factory instances, you gain access to the following Koin ViewModel API:

  • koinViewModel() - fetch instance

For a module that declares a 'MyViewModel' component:

module {
    viewModel { MyViewModel() }
    // or constructor DSL
    viewModelOf(::MyViewModel)
}

We can get your instance like that:

@Composable
fun App() {
    val vm = koinViewModel<MyViewModel>()
}

We can get your instance in function parameters:

@Composable
fun App(vm : MyViewModel = koinViewModel()) {

}
danger

Lazy API is not supported with updates of jetpack Compose 1.1+