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Comment by obeattie | Hacker News Reader

> Inverted mode for displaying cells upside-down (using CATransform) -- a necessary hack for some messaging apps (including ours)

Care to elaborate? Sounds intriguingly crufty.

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UITableView lays out cells from the top. If there aren't enough cells to fill the screen, there will be an empty area in the bottom part of the table view, between the last cell and the bottom of the table view (as you would expect).

Unfortunately, there isn't a standard way to invert a UITableView, and have cells laid out from the bottom.

So, the easiest solution for us was to set the table's transform to CGAffineTransformMake(1, 0, 0, -1, 0, 0) (flip the whole table upside down) and then give the cells the same transform (to cancel out the table view's transform).

A bit hacky, and causes indexPaths to be inverted as well (0,0 is now at the bottom), but worked for us.

Seen a few other people take this approach as well: https://twitter.com/tapbot_paul/status/461161920402563072

That's a pretty interesting approach. Wouldn't it be cleaner to use a UICollectionView with a custom layout?

Most definitely! UICollectionViewLayout should be the right answer, but the thing is: the Slack iOS app was already built using UITableView, drawing many many custom cells. We'll probably port someday to UICollectionView ;)

I've started experimenting not making cells but UIViews and just add them on top of cells. I haven't gone with that fully yet but I've planned to try it out.

The downside is you lose out on many of the out of the box stuff, like cell background highlights that you know have to define yourself.

The upside is that you can now reuse the UIView everywhere, including non-subclasses of ScrollView.

You should add your view to the cell's contentView instead of directly on the cell, which allows you to keep the default behaviors and also reuse the view.

We do the same thing, custom views, mostly drawn in -drawRect:, reused in different cells. It's actually a very nice technique but like you said, the are some sacrifices to take. Still, these cells depend of a tableViewcCell which has unique properties and special APIs that collectionViewCells don't. I think the most trikcy part here is to be able to build a custom UICollectionViewLayout allowing to display cells from the bottom. Haven't found any third-party doing it well enough yet. Do you know of any?

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