How can I update a recycler view of elements from my view model?

Question

How can I update a recycler view of elements from my view model?

ViewModel

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

    fun update(data: Data, isActive: Boolean) {
        // calls a helper function that calls the backend then returns true or false.
        val result: Boolean = callBackend(data, isActive)
    }
}

So when the user clicks an item on the recycler view I will call this update() function. I want to then change the color of the item on the list depending on the result I get from the backend. How should I use LiveData to do that?

Normally if it is only one static element I can do it easily but if this is a recycler view of size n then how could I link it to LiveData?

Answer 1

If you're not using databinding, you can try something like this. Create a new field inside your data object that represents the boolean value for the alternative color. So in your adapter you can do this in you onBind:

override fun onBindViewHolder(viewHolder: ViewHolder, position: Int) {
    val data = adapterList[position]

    if(data.otherColor) {
        viewholder.textView.color = Color.Red
    } else {
        viewholder.textView.color = Color.Black
    }
}

And Then:

// inside your viewModel
private val _singleData = MutableLiveData<Data>()
val singleData: LiveData<Data>
    get() = _singleData

fun update(data: Data, isActive: Boolean) {
    val result: Boolean = callBackend(data, isActive)
    data.otherColor = result
    _singleData.value = data
}

// inside your activity
handlerViewModel.singleData.observe(this, Observer { singleData ->
    val index = adapter.adapterList.indexOfFirst { singleData.id == it.id }
    adapterList[index] = singleData
    adapter.notifyItemChanged(index)
}

Or if you want to observe and update the whole dataset:

// inside your viewModel
private val _allData = MutableLiveData<List<Data>>()
val allData: LiveData<List<Data>>
    get() = _allData

fun update(data: Data, isActive: Boolean) {
    val result: Boolean = callBackend(data, isActive)

    val listToUpdate = allData.value
    listToUpdate.find { it.id == data.id }.otherColor = result

    _allData.value = listToUpdate
}

// inside your activity
handlerViewModel.allData.observe(this, Observer { rvData ->
    adapter.clear()
    adapter.addAll(rvData)
    adapter.notifydatasetChanged()
}