UICollectionViewLayout and method layoutAttributesForItem is never called

Question

I am trying to implement a UICollectionViewFlowLayout or UICollectionViewLayout - any ways the layoutAttributesForItem is never called.

I can see from others that they call layoutAttributesForItem from self.layoutAttributesForItem.

Like this flowout example:

I have created a Playground project you can look at. Overall I am just trying to scale up the center view.

I know it's a very trivial question but I dare ask it. Have you assigned your custom class to the layout of your collectionView correctly? — Adeel Miraj, Oct 19 '16 at 11:33
Thanks for asking :-) If you have the time, have a look at this Playground: https://github.com/JCzz/CollectionView Overall I am just trying to scale the View in the center of the screen. — Chris G., Oct 19 '16 at 11:42
@ChrisG.I'm having the same problem. Everything seems fine except "LayoutAttributesForItem" does not fire at all. I'm not sure why. — jnel899, Jan 10 '17 at 16:41
I never found the solution - let me know if you do. I found that the documentation could be better. — Chris G., Jan 11 '17 at 10:32

score 7 · Answer 1 · answered Feb 23 '17 at 09:55

Try to use it by Sub-Classing UICollectionViewFlowLayout

let flowLayout = LeftAgignedFlowLayout()
flowLayout.minimumLineSpacing = 18
flowLayout.minimumInteritemSpacing = 8
flowLayout.scrollDirection = .vertical
self.collectionViewLayout = flowLayout



class LeftAgignedFlowLayout : UICollectionViewFlowLayout {        

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        let arr = super.layoutAttributesForElements(in: rect)!
        return arr.map {
            atts in 

            var atts = atts
            if atts.representedElementCategory == .cell {
                let ip = atts.indexPath
                atts = self.layoutAttributesForItem(at:ip)!
            }
            return atts
        }
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        var atts = super.layoutAttributesForItem(at:indexPath)!
        if indexPath.item == 0 {
            return atts 

        }
        if atts.frame.origin.x - 1 <= self.sectionInset.left {
            return atts 

        }
        let ipPv = IndexPath(item:indexPath.row-1, section:indexPath.section)
        let fPv = self.layoutAttributesForItem(at:ipPv)!.frame
        let rightPv = fPv.origin.x + fPv.size.width + self.minimumInteritemSpacing
        atts = atts.copy() as! UICollectionViewLayoutAttributes
        atts.frame.origin.x = rightPv
        return atts
    }

}

So what you really proposing here is that we call `layoutAttributesForItem(at:)` ourselves instead of relying the `UICollectionViewFlowLayout` and expect it to callback? :/ — Mohammad Abdurraafay, Jan 22 '18 at 17:01
@MohammadAbdurraafay yes, also if we are using custom flowlayout then it will call this override func. — kalpesh jetani, Jan 24 '18 at 13:09
This is the best example on the Internet (that I can find) of layoutAttributesForItem in swift. — Matt Hudson, Feb 28 '18 at 18:04
It's not a solution anyway, but subclassing FlowLayout didn't change anything. — alekop, Oct 25 '20 at 06:29

UICollectionViewLayout and method layoutAttributesForItem is never called

1 Answers1