ActivityViewModelLazyKt

@MainThread
public static final @NonNull Lazy<@NonNull VM> <VM extends ViewModel> viewModels(
    @NonNull ComponentActivity receiver,
    Function0<@NonNull CreationExtras> extrasProducer,
    Function0<@NonNull ViewModelProvider.Factory> factoryProducer
)

Returns a Lazy delegate to access the ComponentActivity's ViewModel, if factoryProducer is specified then ViewModelProvider.Factory returned by it will be used to create ViewModel first time.

class MyComponentActivity : ComponentActivity() {
    val viewmodel: MyViewModel by viewModels()
}

This property can be accessed only after the Activity is attached to the Application, and access prior to that will result in IllegalArgumentException.