Hello. Can anybody show me how to create a viewmod...

# android

[marlonlom]

Hello.
Can anybody show me how to create a viewmodel that have a function for finding an element using the id returning a flow?
Ive been struggling with this topic, but when executing the app it doesnt return data :(

[Christian Ricardo]

hi @marlonlom! 😄
can you share the code?
why would you need a flow for that? 🤔

[marlonlom]

@Christian Ricardo
The Code:

import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider


class CatalogDetailViewModel(
  private val repository: CatalogDetailRepository
) : ViewModel() {

  fun find(itemId: Long) = repository.find(itemId)

  companion object {

    fun factory(
      repository: CatalogDetailRepository
    ): ViewModelProvider.Factory = object : ViewModelProvider.Factory {
      @Suppress("UNCHECKED_CAST")
      override fun <T : ViewModel> create(modelClass: Class<T>): T {
        return CatalogDetailViewModel(repository) as T
      }
    }
  }
}

[marlonlom]

The flow is for the ui state handling...

[Christian Ricardo]

yeah, but, I mean what would be the use case?
for example, you click an item in the catalog
the view inform that event to the ViewModel and the ViewModel call a Use Case, Action, repository or whatever... and update a MutableState property witch the View is listening
I think it's easiest, the view shouldn't execute logic
if you want a flow, for example for a list of messages you need a MutableStateFlow

[marlonlom]

Yeah, you said it. In my case, its to find a catalog element with additional information. I did use a mutablestateflow, but, in repository ( i did think about usecases, but more classes, more complex -imho- ) the finding/query process builds the detailed info.
I did use a state variable in viewmodel, the thing is: check that while recomposition, handle the case when state its changing/rebuilding 👍🏼

[Christian Ricardo]

Something like this

fun find(itemId: Long) {
        viewModelScope.launch {
            _selectedItem.value = repository.find(itemId)
        }
    }

and the view is observing the selectedItem
what I mean is that find shouldn't return anything