Hello :wave: Is there a way to use HorizontalPager without the lazy loading? Basicly i have a use c...

# compose

[Karlo Vuljanko]

Hello 👋

Is there a way to use HorizontalPager without the lazy loading?
Basicly i have a use case where all my items have to have the height of the tallest item in pager (height of items is dynamic, depends on data i provide to the item), but compose prohibits the use of

IntrinsicSize.Max()

in lazy components. (Understandably)

is there an easy way to work around this or do i have to do some magic with SubcomposeLayout / Create quasi non lazy pager with Row composable?

[Stylianos Gakis]

I’d give it a shot with a normal row, and SnapFlingBehavior https://developer.android.com/reference/kotlin/androidx/compose/foundation/gestures/snapping/SnapFlingBehavior#SnapFlingBehavior[…]mpose.ui.unit.Dp) to get the feeling of a pager as you swipe through, I think that is what it’s for.

I do wonder however if the new Swipable APIs are also a good fit for this, I remember this discussion https://kotlinlang.slack.com/archives/CJLTWPH7S/p1680170260342599 in the past. It seems like it’s part of 1.6.0-alphas here https://developer.android.com/jetpack/androidx/releases/compose-foundation#version_16_2, it’s called AnchoredDraggable it seems.

[Karlo Vuljanko]

thanks for the fast response 😄
i guess ill create my own pager then.
SnapFlingBehavior should suit my needs, i dont need anything fancy just a feel of pager as you stated.
thanks again 🙂

[Karlo Vuljanko]

ill look into AnchoredDraggable but since its still alpha i wouldnt really rely on it yet

[Stylianos Gakis]

Yeah, that sounds like a good idea. If you make it work, I’d really be interested to hear what worked for you in the end 😊

[Karlo Vuljanko]

Sure thing! :)

[Albert Chang]

Here's my non-lazy horizontal pager implementation.
Set offscreenLimit to cover all the pages and you should be able to achieve what you want.

[Karlo Vuljanko]

Thank you! Ill try to make some basic implementation with snap behaviour but ill give your implementation a try as well. Much appreciated.
You sure did put alot of work into it i see

[Stylianos Gakis]

That’s one super helpful snippet right there 😅 Thanks a lot for sharing Albert!

[Colton Idle]

FWIW, Accompanist HorizontalPager used to have it's implementation built in a non-lazy way. Whenever I need it I've copied that into my app. /shrug

[Colton Idle]

Stylianos' suggestion is what I'd probably try first tho

[Stylianos Gakis]

Well Albert literally has a full blown solution here, even supporting accessibility properly and everything, so if it's a serious project I'd definitely go with that first.

[Andrey Kulikov]

there is a beyondBoundsPageCount param on HorizontalPager from compose:foundation. but keep in mind that loading a lot of pages at once will affect your performance. sometimes a more reasonable approach is to react on size changes nicely, like with having animateContentSize modifier on Pager, or something like this

[Lukasz Kalnik]

I'm dropping my simple solution using SubcomposeLayout and the regular, lazy HorizontalPager here, in case someone finds this thread:

fun OnboardingPager(onboardingCards: List<OnboardingCardState>) {
    val pagerState = rememberPagerState(pageCount = { onboardingCards.size })
    var maxCardHeight by remember { mutableStateOf(0.dp) }
    val pagerContentPadding = 16.dp

    // Measure the maximum height of all cards
    SubcomposeLayout { constraints ->
        val measuredHeights = onboardingCards.map { card ->
            val placeables = subcompose(card) {
                OnboardingCard(
                    onboardingCard = card,
                    modifier = Modifier.padding(horizontal = pagerContentPadding)
                )
            }.map { it.measure(constraints) }

            placeables.maxOf { it.height.toDp() }
        }

        maxCardHeight = measuredHeights.maxOrNull() ?: 0.dp
        layout(0, 0) {}
    }

    HorizontalPager(
        state = pagerState,
        pageSpacing = 16.dp,
        verticalAlignment = Alignment.Top,
        contentPadding = PaddingValues(horizontal = pagerContentPadding),
    )
    { page ->
        OnboardingCard(
            onboardingCard = onboardingCards[page],
            modifier = Modifier.height(maxCardHeight)
        )
    }
        // ...

[Lukasz Kalnik]

SubcomposeLayout just measures all the `OnboardingCard`s here, which are displayed in HorizontalPager.
It is important to pass the same constraints to the `OnboardingCard`s inside the SubcomposeLayout, that's why I pass the pagerContentPadding both to the card in the SubcomposeLayout and to the HorizontalPager itself.
Otherwise the card will assume it has more horizontal space and will cut off the content of the highest pages in the HorizontalPager.

[Lukasz Kalnik]

SubcomposeLayout is executed during layout phase, after measuring and before placing items.
It doesn't draw anything on the screen. It's sole purpose is if you need to measure some Composables (e.g. here the OnboardingCard) to pass the result to some other Composable (here it is passed to the OnboardingCard inside the HorizontalPager in the Modifier.height(maxCardHeight)).

[Andrey Kulikov]

it is very inefficient as we compose and measure all the pages multiple times. you can achieve this behavior more efficiently by just passing an itemsCount as beyondBoundsPageCount for HorizontalPager

[Lukasz Kalnik]

How do I set the page height then to be the same for all pages?

[Lukasz Kalnik]

Just setting the itemsCount to beyondViewportPageCount didn't fix the problem

[Lukasz Kalnik]

I want to set the page height to be all equal

[Lukasz Kalnik]

Not that the HorizontalPager height doesn't change

[Lukasz Kalnik]

This is easy, but doesn't solve the problem

[Lukasz Kalnik]

Or can I then set Modifier.height(Intrinsics.Max) to the pages, because they all will be composed eagerly then?

[Lukasz Kalnik]

So like this:

HorizontalPager(
    // ...
    beyondViewportPageCount = itemsCount
    // ...
) { page ->
    Page(Modifier.height(IntrinsicsSize.Max))
}

[Andrey Kulikov]

ok, I agree. beyondBoundsPageCount is helpful to set the size of the parent to the max height. but to also size each page for this max we need to use intrinsics, and there is no api for that for now. we track this request in https://issuetracker.google.com/issues/259686541. it mentions grids, but the same is true for all the lazy layouts. feel free to mention your case there as a comment

[Lukasz Kalnik]

Thank you!