Purpose and difference of Key and Pivotal ?

# compose

[amar_1995]

Purpose and difference of Key and Pivotal ?

[Manuel Wrage]

Pivotal is the mechanism which is used to implement the key function.

[amar_1995]

I am making infinite scrolling view.
After making to the end of verticalScroller. I am calling api to load more data and store it in a local db.
I am observing the local db and as change happen i recieved a new list of data(with old data also).
Now the problem is that scroller is recomposing the whole view. I only want the data to load with new ids.
Is using Key or Pivotal helps ?

[amar_1995]

I don't want to recompose the whole ui.

[Manuel Wrage]

Is every parameter of your item composable stable?

[amar_1995]

I am getting list of livedata which is observed inside a below function

fun <T> observer(data: LiveData<T>) = effectOf<T?> {
    var result = +state<T?> { data.value }
    val observer = +memo { Observer<T> { result.value = it } }

    +onCommit(data) {
        data.observeForever(observer)
        onDispose { data.removeObserver(observer) }
    }
    result.value
}

[Manuel Wrage]

Can you show me code were you compose the VerticalScroller?

[amar_1995]

var internationalState = +observer(newArticleModel.internationalHeadline)
Surface(color = (+MaterialTheme.colors()).surface, modifier = Expanded) {
    if (internationalState == null) {
        ShowLoading()
    } else if (internationalState.isEmpty()) {
        NoContentMore()
    } else {
        val scrollerPosition: ScrollerPosition = +memo { ScrollerPosition(0f) }
        println("MainActivity data here : " + internationalState)

        Observe {
            +onCommit(scrollerPosition.isAtEndOfList) {
                println("Is commit entered")
                if(scrollerPosition.isAtEndOfList)
                    newArticleModel.loadMoreData()
            }
        }
        VerticalScroller(scrollerPosition = scrollerPosition) {
            Column(Expanded) {

                println("Page rendering size " + PageSize.topHeadlineInternationalPageNo)
                internationalState!!.forEach {
                    Ripple(bounded = true) {
                        Clickable() {
                            ArticleTicket(
                                backgroundColor = (+MaterialTheme.colors()).background,
                                article = it
                            )
                        }
                    }
                }
            }
        }
    }
}

[Manuel Wrage]

1. Extract the logic inside the forEach to a function that accepts your article class as a parameter
2. Annotate the article with @Pivotal
3. Annotate the article class with @Immutable, @Stable or @Model depending on what is applicable. I guess it's @Immutable in this case

[amar_1995]

Getting this error

java.lang.IllegalStateException: Expected a group start
        at androidx.compose.SlotTableKt.getAsGroupStart(SlotTable.kt:641)
        at androidx.compose.SlotTableKt.access$getAsGroupStart$p(SlotTable.kt:1)

[Manuel Wrage]

You have to use the latest version of compose

[amar_1995]

Okay, let me try after updating the compose

[amar_1995]

After changing from dev03 to dev04, I am getting this error
java.lang.ClassCastException: androidx.compose.GroupStart cannot be cast to androidx.ui.foundation.ScrollerPosition