When swiping this, I would have expected that every “remember page” log is only shown once. However,...

# compose

[Paul Woitaschek]

When swiping this, I would have expected that every “remember page” log is only shown once. However, once swiping or just dragging a page a little left and right, the block gets called again and again.

Is that expected behavior? Is there a way to remember something depending on the page?

HorizontalPager(
    modifier = Modifier.fillMaxSize(),
    pageCount = 42
) { currentPage ->
    remember(currentPage) {
        Log.d("remember", "remember page $currentPage")
        42
    }
    Text(
        modifier = Modifier.fillMaxSize(),
        text = "Page $currentPage"
    )
}

[Paul Woitaschek]

If I make use of rememberSaveable, this works as I want. However the thing I want to remember (a presenter) actually is not saveable.

[ephemient]

https://newsletter.jorgecastillo.dev/p/movablecontentof-and-movablecontentwithreceivero is one solution

[Albert Chang]

This is the expected behavior, and I don't think movable content will help here, as movableContentOf doesn't prevent the content inside from being disposed when the call to the movable content is disposed. You can just set a appropriate beyondBoundsPageCount to make sure the pages are not disposed.

[Paul Woitaschek]

I tried that but when I touch a pager and drag it by a few pixels left or right it makes my app really laggy as it composes the whole time while dragging and state seems to be discarded

[Paul Woitaschek]

For that specific thing one solution I came up with (and which works) is to have my own memory cache for the objects I’m persisting, but what I really want is some:
rememberSaveableInMemoryOnlyAndIgnoreBundlePersistence

[ephemient]

movableContentOf will help if you move the content outside of the pager

[Albert Chang]

No it won't. You can try it yourself.

[Albert Chang]

val content = remember { movableContentOf { ... } }
content() // When this call is disposed (and not moved to anywhere else), content inside will also be disposed

[Albert Chang]

And to OP, the rememberSaveableInMemoryOnlyAndIgnoreBundlePersistence you want is probably just something as simple as

val map = remember { mutableMapOf<Int, Something>() }
HorizontalPager { currentPage ->
    map.getOrPut(currentCompositeKeyHash) {
        Something()
    }
}

[Paul Woitaschek]

Yep that’s what I went with 👌