Inject ViewModel using Dagger 2 + Kotlin + ViewModel

Question

class SlideshowViewModel : ViewModel() {

@Inject lateinit var mediaItemRepository : MediaItemRepository

fun init() {
    What goes here?
}

So I\'m tr

Answer 1

You can enable constructor injection for your ViewModels. You can check out Google samples to see how to do it in Java. (Update: looks like they converted the project to Kotlin so this URL no longer works)

Here is how to do a similar thing in Kotlin:

Add ViewModelKey annotation:

import android.arch.lifecycle.ViewModel

import java.lang.annotation.Documented
import java.lang.annotation.ElementType
import java.lang.annotation.Retention
import java.lang.annotation.RetentionPolicy
import java.lang.annotation.Target

import dagger.MapKey
import kotlin.reflect.KClass

@Suppress("DEPRECATED_JAVA_ANNOTATION")
@Documented
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@MapKey
internal annotation class ViewModelKey(val value: KClass)

Add ViewModelFactory:

import android.arch.lifecycle.ViewModel
import android.arch.lifecycle.ViewModelProvider

import javax.inject.Inject
import javax.inject.Provider
import javax.inject.Singleton

@Singleton
class ViewModelFactory @Inject constructor(
    private val creators: Map, @JvmSuppressWildcards Provider>
) : ViewModelProvider.Factory {

    @Suppress("UNCHECKED_CAST")
    override fun  create(modelClass: Class): T {
        var creator: Provider? = creators[modelClass]

        if (creator == null) {
            for ((key, value) in creators) {
                if (modelClass.isAssignableFrom(key)) {
                    creator = value
                    break
                }
            }
        }

        if (creator == null) {
            throw IllegalArgumentException("unknown model class " + modelClass)
        }

        try {
            return creator.get() as T
        } catch (e: Exception) {
            throw RuntimeException(e)
        }
    }
}

Add ViewModelModule:

import dagger.Module
import android.arch.lifecycle.ViewModel
import dagger.multibindings.IntoMap
import dagger.Binds
import android.arch.lifecycle.ViewModelProvider
import com.bubelov.coins.ui.viewmodel.EditPlaceViewModel

@Module
abstract class ViewModelModule {
    @Binds
    @IntoMap
    @ViewModelKey(EditPlaceViewModel::class) // PROVIDE YOUR OWN MODELS HERE
    internal abstract fun bindEditPlaceViewModel(editPlaceViewModel: EditPlaceViewModel): ViewModel

    @Binds
    internal abstract fun bindViewModelFactory(factory: ViewModelFactory): ViewModelProvider.Factory
}

Register your ViewModelModule in your component

Inject ViewModelProvider.Factory in your activity:

@Inject lateinit var modelFactory: ViewModelProvider.Factory
private lateinit var model: EditPlaceViewModel

Pass your modelFactory to each ViewModelProviders.of method:

model = ViewModelProviders.of(this, modelFactory)[EditPlaceViewModel::class.java]

Here is the sample commit which contains all of the required changes: Support constructor injection for view models