I’m relatively new to Android development. While designing the application, I encountered some problems. Everything I found did not quite cover my needs. I would like to listen to your pieces of advice. So, okeeey let’s go!

The main screen displays a list of dishes for a specific category. I would like the icon on the items I added to the database to update.

Model:

data class MealModel(
    val id: String,
    val name: String,
    val image: String,
    val isSaved: Boolean = false,
)

Resource via State:

sealed class Resource<T>(
    val data: T? = null,
    val message: String? = null,
) {
    class Success<T>(data: T) : Resource<T>(data)
    class Error<T>(message: String?, data: T? = null) : Resource<T>(data, message)
    class Loading<T> : Resource<T>()
}

ViewModel:

@HiltViewModel
class HomeViewModel @Inject constructor(
    private val getMealsUseCase: GetMealsUseCase,
    private val isMealInSavedUseCase: IsMealInSavedUseCase,
    private val addOrRemoveMealUseCase: AddOrRemoveMealUseCase,
    private val dispatcher: CoroutineDispatcher = Dispatchers.IO,
) : ViewModel() {
    private val _meals = MutableStateFlow<Resource<List<MealModel>>>(Resource.Loading())
    val meals: StateFlow<Resource<List<MealModel>>> = _meals.asStateFlow()

    fun getMeals() {
        getMealsUseCase.invoke(category = category)
            .onEach { resource ->
                when (resource) {
                    is Resource.Loading -> {
                        _meals.value = Resource.Loading()
                    }

                    is Resource.Success -> {
                        if (resource.data != null) {
                            _meals.value = Resource.Success(resource.data)
                        }
                    }

                    is Resource.Error -> {
                        _meals.value = Resource.Error(resource.message)
                    }
                }
            }
            .launchIn(viewModelScope)
    }

    fun savedIconClicked(meal: MealModel) {
        viewModelScope.launch(dispatcher) {
            addOrRemoveMealUseCase.addOrRemoveMeal(meal)
        }
    }
}

After searching for an answer, I realized that I could do something like this:

val index = _meals.value.data!!.indexOf(item)
val items = _meals.value.data!!.toMutableList()
items[index] = items[index].copy(isSaved = item.isSaved.not())
_meals.value.data = items

The truth is that the problem arises in Resource. The data is val due to which I cannot assign a new list. If you make a var everything works according to the logs.

And now inside the function getMeals(), when the state is successful, it looks like this:

is Resource.Success -> {
    if (resource.data != null) {
       _meals.value = Resource.Success(resource.data!!)
    }
    for (item in resource.data!!) {
        if (isMealInSavedUseCase.isMealInSaved(item.id)) {
           val index = _meals.value.data!!.indexOf(item)
           val items = _meals.value.data!!.toMutableList()
           items[index] = items[index].copy(isSaved = item.isSaved.not())
           _meals.value.data = items
        }
    }
}

But, firstly, changing data in Resource is probably not particularly advisable. Secondly, when requesting again, the list will be updated again with MealModel elements with the isSaved = false. That is, we will not notice any attempts to change the added element. And thirdly, I don’t really understand how dynamically the add icon should be updated. Working with list elements is in the adapter, but we cannot add LiveData there, which will store a specific icon.

Finally, for understanding, I’ll show you what a list element looks like: