Step #5: Updating SingleModelMotor

We need to make similar adjustments to SingleModelMotor that we made to RosterMotor.

With that in mind, add this view-state class above the declaration of SingleModelMotor:

data class SingleModelViewState(
  val item: ToDoModel? = null
)

And, replace the current SingleModelMotor implementation with:

class SingleModelMotor(
  private val repo: ToDoRepository,
  modelId: String?
) : ViewModel() {
  val states = repo.find(modelId)
    .map { SingleModelViewState(it) }
    .stateIn(viewModelScope, SharingStarted.Eagerly, SingleModelViewState())

  fun save(model: ToDoModel) {
    viewModelScope.launch {
      repo.save(model)
    }
  }

  fun delete(model: ToDoModel) {
    viewModelScope.launch {
      repo.delete(model)
    }
  }
}

SingleModelViewState is akin to RosterViewState, wrapping a single model object… or null, since we may not have a model (e.g., for a new to-do item).

states works like the RosterMotor edition, except that it calls find() on the ToDoRepository rather than all(). But, like RosterMotor, it maps the result to a view-state and it converts the Flow into a StateFlow.

save() and delete() both wrap their corresponding ToDoRepository calls in viewModelScope.launch(), so that those coroutines get run in our desired CoroutineScope.