Does not work properly with auto layout cell sizing

[damienrambout]

When I set a estimatedItemSize on the collection view layout and use auto-layout to define the size of my cells (hence, not implementing - (CGSize)collectionView:layout:sizeForItemAtIndexPath:), KTCenterFlowLayout does not work anymore.

Since iOS 8, it's very usual to use auto-layout for UICollectionViewCell automatic sizing (as well as UITableViewCell automatic height).

[keighl]

Hey @damienrambout. Thanks for that. I'm not familiar with what UICollectionViewFlowLayout does under the hood exactly in that case.

This class just hijacks the layoutAttributesForElementsInRect method on flow layout. I would sort of expect all the sizing to be determined at that point (auto-layout or otherwise). But there are probably differences that we need to account for.

I will investigate when I can. Feel free to dig deeper!

[bsantanas]

Thank you very much! I spent the last two days trying to figure out why my swift implementation wasn't working and now I see this post... I came to the exact same conclusion that @damienrambout pointed out. If you come up with something please let me know! I'll do the same.
Cheers!

[thinalgal]

One solution, which is not efficient but works, is to use the existing implementation of layoutAttributesForElementsInRect to implement layoutAttributesForItemAtIndexPath, by defining a rect that grabs all elements and then just picking out the one you want using its indexPath, as follows:

override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes! {
        let modifiedLayoutAttributes = self.layoutAttributesForElementsInRect(CGRectInfinite)

        if let desiredLayAttr = modifiedLayoutAttributes?.filter({ indexPath.isEqual($0.indexPath) }).first as? UICollectionViewLayoutAttributes {
            return desiredLayAttr
        }
        else
        {
            NSLog("error")
            return super.layoutAttributesForItemAtIndexPath(indexPath)
        }
    }

[niklassaers]

Hi guys, I am running into the same issue with auto-layout based cells, but I believe I have come a good way at hunting this down.

When I am laying it out, I don't get the nice spacing I used to before individual cell sizing, I can get to getting nice spacing if I in

func preferredLayoutAttributesFittingAttributes(layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes

just return layoutAttributes. However, when I have a implementation that returns the size I want, the layout collapses to this:

The really interesting thing is that if I rotate, and then rotate back, I get the expected look:

You can find the project here: https://github.com/skylib/SnapTagsView/tree/DemoForKTCenterFlowLayout and the function referred to above lives in SnapTagsView/SnapTagCell.swift. Just run the example app in it and you'll see exactly what I mean. (you'll need to do a pod install before compiling it)

Cheers

[keighl]

thanks @niklassaers i'll check it out

[iliaskarim]

I'm also noticing that this layout class does not seem to work with auto sizing collection view cells.

Anyone know any alternatives? 😅 I'll probably just be left-aligning for now