viewModel.kt

class TestViewModel(application: Application) : AndroidViewModel(application) {

    private var dataLiveData = MutableLiveData<Int>()

    var data = dataLiveData as LiveData<Int>

    private val roomDb = RoomDb.getInstance(application).getUserDao()

    fun insertUser(user: User) {
        roomDb.insertUser(user)
    }

    fun deleteUser() {
        roomDb.deleteUser()
    }

  ..
  ..

}