When UICollectionViewLayer is set, cellForItemAt doesn't called

Question

I want to set UICollectionViewLayout for my UICollectionView but when the layer is set, the function cellForItemAt doesn't called. I don't understand why. My UICollectionView is in a XIB, with this code for testing the UICollectionViewLayout :

required init?(coder aDecoder: NSCoder)
{
    super.init(coder: aDecoder)
    xibSetup()

    self.collectionView.register(UINib(nibName: "StepCell", bundle: nil), forCellWithReuseIdentifier: stepCellIdentifier)
    self.collectionView.delegate = self
    self.collectionView.dataSource = self
}

func numberOfSections(in collectionView: UICollectionView) -> Int {
    return 3
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 100
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    if let lCell = collectionView.dequeueReusableCell(withReuseIdentifier: stepCellIdentifier, for: indexPath) as? StepCell {
        lCell.text.text = indexPath.row.description
        return lCell
    }
    return UICollectionViewCell()
}

I have a custom UICollectionViewCell in another xib and this is my UICollectionViewLayout class :

class DetailGroupCollectionviewLayout: UICollectionViewLayout {
    let CELL_HEIGHT = 30.0
    let CELL_WIDTH = 100.0

    var cellAttrsDictionary = Dictionary<IndexPath,UICollectionViewLayoutAttributes>()
    var contentSize = CGSize.zero

    override var collectionViewContentSize: CGSize {
        return self.contentSize
    }

    override func prepare() {
        if let lCollectionView = self.collectionView {
            if lCollectionView.numberOfSections > 0 {
                for section in 0...lCollectionView.numberOfSections - 1 {
                    if lCollectionView.numberOfItems(inSection: section) > 0 {
                        for item in 0...lCollectionView.numberOfItems(inSection: section) - 1 {
                            let cellIndex = IndexPath(item: item, section: section)
                            let xPos = Double(item) * CELL_WIDTH
                            let yPos = Double(section) * CELL_HEIGHT

                            let cellAttributes = UICollectionViewLayoutAttributes(forCellWith: cellIndex)
                            cellAttributes.frame = CGRect(x: xPos, y: yPos, width: CELL_WIDTH, height: CELL_HEIGHT)
                            cellAttributes.zIndex = 1

                            cellAttrsDictionary[cellIndex] = cellAttributes
                        }
                    }
                }
            }
        }
    }
}

I have tried to have everything about the UICollectionView in storyboard because i was thinking that a xib "bug" but this resolve nothing.

There is a thing that i don't make correctly or a particularity ? I'm lost.

I'm on Xcode 8.3 with Swift 3.1 and my app is on iOS 10.

Answer 1

I find the solution, my custom UICollectionViewLayout has no contentSize, I added this in my prepare() function :

let contentWidth = Double(collectionView!.numberOfSections) * CELL_WIDTH
let contentHeight = Double(collectionView!.numberOfItems(inSection: 0)) * CELL_HEIGHT
self.contentSize = CGSize(width: contentWidth, height: contentHeight)

This is the result