Office Hours Transcript: 2021-07-10

Hello Mark!

sorry if I am asking a lot in this period, is the most delicate moment of my career, thank you very much today for your altruistic help on SO about my paging problem

Is my first real ticket on Flows and coroutines, and I cannot send the data from the paging to the adapter
I have a button and on click I trigger the paging “call” from the fragment to the view model
And I see that the adapter, namely the adapter.submitData(pagedData) is called only when I initialise the button on press, but not when the data are retrieved

This is myFragment

fragment_points_card_constraint_layout.setOnClickListener {
    GlobalScope.launch(Dispatchers.IO) {
        try {
            pointViewModel.fetchThat(openIdAuthHandler.getMWiseUserId.value!!).collectLatest { pagingData ->
                Timber.i("IVOZZ pagingData :$pagingData")

                pointAdapter.submitData(pagingData)
            }
        } catch (e: Exception) {
            Timber.i(" IVOZZ exception flow: $e")
        }
    }
}

and this is the viewModel

class PointViewModel(val networkClient: NetworkClient) : ViewModel() {

    fun fetchThat(userId: String) = Pager(PagingConfig(pageSize = 1)){
        PointsTransactionsSource(networkClient, userId)
    }.flow.cachedIn(viewModelScope)
}

I think i run in an execution reactive problem, and cannot find why is happening

ok

ah i read that is possible to use also rxjava indeed, there are also dedicated dependencies

well will found a way to understand

yes I found this approach on the internet

anyway does not matter I would like to ask you about the diffCallback in the adapter

override fun areItemsTheSame(oldItem: PointsItem, newItem: PointsItem): Boolean =
oldItem.id == newItem.id

as my object does not have any identifier, and as is still not working the adapter I added a bogus variable val id :Int? in the object

but was just to test

could you confirm that I can just use the diff util with oldItem == newItem for areItemsTheSame` ?

without adding a fake id in the model /data class?

PointsItem is the list of objects that is coming from the back end and in principle does not have any identifier as an id

but just some proprieties

yes it is

data class PointsItem(
    val id :Int,//temp
    @SerializedName("eventDate")
    val eventDate: String?,
    @SerializedName("eventId")
    val eventId: String?,
    @SerializedName("group")
    val group: String?,
    @SerializedName("iconName")
    val iconName: Any?,
    @SerializedName("name")
    val name: String?,
    @SerializedName("points")
    val points: Double?,
    @SerializedName("transactionAmount")
    val transactionAmount: Double?,
    @SerializedName("transactionCurrency")
    val transactionCurrency: String?
)

ah I see

thank you

and there is another thing I do not get although my researches

as you can see from the method in the VM i pasted above I give a PagingCOnfig parameter in this case pageSize 1 ```fun fetchThat(userId: String) = Pager(PagingConfig(pageSize = 1)){
PointsTransactionsSource(networkClient, userId)
}.flow.cachedIn(viewModelScope)

the documentation says

     * Defines the number of items loaded at once from the [PagingSource].
     *
     * Should be several times the number of visible items onscreen.
     *
     * Configuring your page size depends on how your data is being loaded and used. Smaller
     * page sizes improve memory usage, latency, and avoid GC churn. Larger pages generally
     * improve loading throughput, to a point (avoid loading more than 2MB from SQLite at
     * once, since it incurs extra cost).

yes I am experimenting

I will giggle a bit

well Mark still thank you for your help today here and in SO

but this 25 what is in the old adapter world?

is the size of the items showed before to load again swiping down?

ah

I understand, so is me that decide how is a page in the PagingSource not the back end

ok thank you to share

this item makes things easier, was a nightmare before, but could not understand how the black magic was performed, now my ideas are a bit clearer

yes callback are toxic

I know i went desperatly through all your books today

you did also something with graph sql

about pagination but not with paging library

sorry? Mark you do miracles to update everything

is just that not being familiar I just tried to copy paste the tutorials could find and twickling them and prey

but now `i understand that is a beautiful library

tweaking* sorry

hello again sorry my daughter took the mouse and closed the door

window

I can’t think of one

Just dropping by

Hi Sudokai

Bye Mark and Sudokai, thanks again

you too