How to use dependency injection for injecting constructor in a ViewModel

Question

I am trying to implement the example on https://developer.android.com/jetpack/docs/guide. This explains how tan android app should be structured.

When I use the same

Answer 1

If you want to provide viewmodel with constructor as a dependency in your Fragment, there is a different method for it,

Lets suppose you have a viewmodel class as belows,

class SampleViewmModel(dataManager:DataManager):ViewModel(){
  //some logic
}

Then you will need to create a factory class to support above viewmodel like below,

class SampleFactory @Inject constructor(var dataManager:DataManager): ViewModelProvider.Factory {
override fun <T : ViewModel?> create(modelClass: Class<T>): T {
    if (modelClass.isAssignableFrom(SampleViewModel::class.java)) {
        return SampleViewModel(dataManager) as T
    }
    throw IllegalStateException()
}

}

Now in your module class, you can inject above classes as below, (Note-Datamanager class is injectible)

//Provide Factory
@Provides
fun provideFactory(dataManager:DataManager): SampleFactory {
    return SampleFactory(dataManager)
}

//Provide actual viewmodel
@Provides
fun provideViewModel(sampleFactory: SampleFactory): SampleViewModel {
    return ViewModelProviders.of(fragment, sampleFactory)[SampleViewModel::class]
}

No in your Fragment, you can inject your viewmodel just like any other dependency,

@Injetct
lateinit viewModel:SampleViewModel

Answer 2

You can use Koin as an alternative for Dagger. Koin have full support of Android Architecture ViewModel. It's extremely easy to use. I prefer it for small and mid-sized project.

// declared ViewModel using the viewModel keyword
val myModule : Module = module {
    viewModel { MyViewModel(get()) } 
    ...
}

// Just get it
class MyActivity() : AppCompatActivity() {

    // lazy inject MyViewModel
    val myViewModel : MyViewModel by viewModel()
}

insert-koin.io