Hi, I've been playing around trying to implement recycler "view" on Compose and this far for now: https://gist.github.com/ShikaSD/30ce3afc9376767f9ac090457733f627 Currently it only scrolls down and displays items correctly if you do it slowly 🙂 I have encountered an issue that layout in compose cannot add children synchronously. E.g. if recycler has some space at the bottom, it cannot be sure how many items it should lay out at once, as you cannot add and measure new items in the middle of layout pass. Currently my workaround is to keep a window of visible elements and increase/decrease it when items go out of the visible area. However, I add elements one by one (as I don't know how much space they will take) which is a bit slow (and require multiple passes to fill the screen for the first time). Do you have any suggestions on how to approach this better?

This is a complex and challenging component to implement on your own and besides to get it right you will need to do a lot of hard work to cover a lot of edge cases. You can wait for ScrollingList implementation that will come with future releases of compose if you not in a hurry. Otherwise you will have to first understand the detailed implementation of how the Recycler works in the current recyclerview before you can attempt to roll out your own recycler view. Check the talks done by Romain Guy and Adam Powell on recycler views where they discuss how they are implemented.

Naively I'd assume that since there are no actual objects to keep in pools and recycle, it's enough to know what Composables are in the visible window and just invoke rendering those, and much of the magic of RecyclerView doesn't need to be understood / applied here.

You probably want to start from

WithConstraints

rather than

Layout

, it lets you determine the composition of children at layout time

Not sure it will help much. The problem is that

WithConstraints

works quite similar to

Layout

, it operates based on external constraints only. I am looking for something which allows adding more nodes into composition based on layout results (like lazy composable maybe?)

ah, you're right. I'm thinking of the other component in progress that's meant to help with this 🙂 should be coming soon

I actually managed to find a workaround after modifying

WithConstraints

. Essentially, you can use

subcompose

to create new nodes whenever needed and measure/layout them straight away.

Can you show the newer version with the modified WithConstraints function?

Now it is highly unstable (I encountered like 5 different crashes scrolling down so far), so will try to fix that first.

I already tried tons of different thinks to make a Recyclerview like component. I hope you have more luck 👍

Yeah, I had like 30 problems related to that in 3 hours I spent on this

not much to elaborate on, we need a variant of Layout/WithConstraints that does just-in-time composition so that you can write the layout code to fill available space the way ListView/RecyclerView do. Exact shape of the API is TBD but it's probably going to look a lot like Layout/WithConstraints