is it possible to have variable element height?

[trungpham]

I'm looking at a few different scroll list component. None of them seems to support variable element height.

[nmn]

react-infinity doesn't currently have variable height support. That said I'm building version 2.

I'm trying to decide whether to add support to react-infinity or just build a separate component.
The basic challenge comes down to calculating the height dynamically from the DOM in a performant way.

Do you think you would want a component where you have to pass the element height?

[mablack]

That would fit the use case that I have; I need to render a list of maybe 3 different components, and I know the height of each type of component in advance.

[nmn]

I should be able to handle that in v2. It will take a couple of weeks to be done.

[pandaiolo]

+1 for pinterest-like layout !

Also, my use case is the same : I can provide the element height. However, for use cases when the height is unknown, there is already masonry. There is a react component, react-masonry-mixin, not sure how it can play with react-infinity.

[nmn]

Thanks for the feedback.

Here are my thoughts on the topic, if I can get some consensus, I can add pinterest like layout soon.

• The main problem with layout + animation + offscreen culling is knowing the size of the elements
• In react-infinity, I ask for a global size attribute to solve the problem and make calculations simple
• Instead (or with an option) I can get the size of elements from the data being used to render the elements. With this if there are variable sized elements, I can easily do a pinterest-like layout
• It would still be impossible to do flexible layouts (where the width of elements changes with available width) as that basically makes layout totally unpredictable
• As for a masonry like system for rendering elements where size is not known, I could use a temporary hidden buffer to render them just to get their size before rendering them for real. This would be pretty complicated to implement. Another solution, that I have used for smaller set of elements is to render with a default size for all elements, and then letting the elements call a callback with their actual size and constantly re-adjust the layout position with that. Even with this, culling off-screen elements can be quite a problem. Also with the large number of DOM operations to getSize, there would be a big performance hit.

As I mentioned, I'm working on v2 or react-infinity, with better API, documentation and an example playground. I'm thinking of now adding just the simple case for pinterest-like layouts where you can pass in the size of elements with the data.

But the new code-base is based on smaller components, and all non-essential part of the code like handling scrolling and window-resizes has been factored out into a wrapper component. I can see the buffer system working as another wrapper component.

Let me know your feedback on these things.

[natew]

What about a solution where you give a "range" of heights. Another solution would be having the elements tell their height in advance. In all honesty that solves 99% of use cases.

First one is say you have a list with titles, some titles are 1 line, some up to 4. You could specify (minHeight: 50, maxHeight: 100) and react-infinity would just assume the worst-case scenario and keep that many elements in the DOM.

The other case is for example the twitter feed with images. Some elements are fixed at one size, while others are fixed at a much bigger size. In that case why not have your data objects keep the size inside them. Each element in the array has .size. We know all picture ones are scaled down, while all text ones are fixed at another size.

I know some people would want truly dynamic, but like I said I think this solves just about all options and avoid the #1 no-no: don't touch the DOM.

By the way I'm working on integrating this with reapp.io list views am impressed with usage on the Scribbler. I'm running into some troubles though, has it been tested with a recent version of React (I'm using 0.13 beta)? I can open a ticket but I've run into two issues so far, the second which seems a bit hard to debug.

[natew]

Also want to say if you develop v2 in the open I'd be happy to jump in. Infinite lists are a big feature for what I'm building and I'd love to chip in.

[nmn]

@natew I'm primarily looking at the solution where the size would passed with the data. This is the solution you are talking about as well.

I guess, I'll hold off on the more dynamic solutions for now.

As for developing in the open, I'll push my work on a new branch so you and others can chip in. I should have done this a long time ago, thanks for the reminder.

The main concern is I would need to explain the new architecture I have in mind, but I can write a quick readme to explain that.

[nmn]

Another interesting thing to note:

React-Canvas has a helper to get the size of text. You give it some text, font-size and font-family and available width, and it tells you the resulting height. This done using an offscreen canvas, so it's much faster than the DOM.

Keeping that in mind, I would like to add a method, where your child component can have a static method that can accept props and return the size.

[nmn]

Also, as for the issues you've faced, I have done ZERO testing on 0.13.
I tend to wait for releases to become stable to test on them.

But it seems to work fine on 0.12.2 for me.

(BTW the implementation on the Scribbler is getting old too, I need to update that)

[nmn]

quick update, I think I know the issue with 0.13, I was using react/lib/mergeInto which has been removed in 0.13

That is at least one of the issues.

[natew]

Going to check this out again today. This demo would really be killer with reapp. Excited for 2.0.

[natew]

By the way after a quick glance, any way you can make the animations an optional piece? We have a requestAnimationFrame animation mixin already built in that I'd use to integrate. This isn't super important, I could submit a pull request once 2.0 comes out.

[nmn]

@natew animations are supposed to be optional. I always factor out my libraries from real projects. As of now, all the work to put a good API is still pending.