https://github.com/joecks/android-architecture/blob/dev-todo-mvvm-single-live/todoapp/app/src/main/java/com/example/android/architecture/blueprints/todoapp/main/MainViewModel.kt

MainViewModel.kt

class MainViewModel : BaseReactViewModel<Data>(), TasksActions, AddEditActions {

    override val initialViewData = TasksData

    override fun onSaveTask() {
        updateViewData(TasksData)
    }

    override fun onTaskDetails(taskId: String) {
        updateViewData(EditTaskData(taskId))
    }

    override fun onNewTask() {
        updateViewData(NewTaskData)
    }

    fun onBackPress(): Boolean {
        return when (viewData.value) {
            NewTaskData, is EditTaskData -> {
                updateViewData(TasksData)
                true
            }
            else -> false
        }
    }
}