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SOLVED: [Swift5/iOS13+/UIKit] UICollectionView & DiffableDataSource & flowLayout: how to add a header?

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No Storyboard! I have a collectionView with a diffeable datasource. Only one section. I want to display a header, so I registered a custom cell class:

collectionView.register(SectionHeader.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: SectionHeader.reuseidentifier)

I create a flow Layout as such:

    private func createFlexibleFlowLayout(in view: UIView) -> UICollectionViewFlowLayout {
        let width = view.bounds.width
        let padding: CGFloat = 12
        let minimumItemSpacing: CGFloat = 10
        let availableWidth = width - (padding * 2) - (minimumItemSpacing * 2)

        let itemWidth = traitCollection.horizontalSizeClass == .compact ? availableWidth / 2 : availableWidth / 3

        let flowLayout = UICollectionViewFlowLayout()
        flowLayout.sectionInset = UIEdgeInsets(top: padding, left: padding, bottom: padding, right: padding)
        flowLayout.itemSize = CGSize(width: itemWidth, height: itemWidth + 40)

        flowLayout.sectionHeadersPinToVisibleBounds = true

        return flowLayout
    }

The datasource looks as follows:

    func createDataSource() {
        dataSource = UICollectionViewDiffableDataSource<Section, Project>(collectionView: collectionView) { (collectionView, indexPath, project) in
                return self.configure(NormalProjectCell.self, with: project, for: indexPath)
        }

        dataSource?.supplementaryViewProvider = { (collectionView, kind, indexPath) in
            guard let sectionHeader = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: SectionHeader.reuseidentifier, for: indexPath) as? SectionHeader else {
                fatalError("Could not dequeue sectionHeader: \(SectionHeader.reuseidentifier)")
            }

            sectionHeader.title.text = "Tap and hold to edit an existing Project!"
            sectionHeader.subtitle.text = "tap to view Project notes"
            return sectionHeader
        }
    }

But how and where do I add the header? The 'old way' doesn't work:

override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {(...)}

I'm stumped!

3      

@emin  

Maybe you are missing the height for that Header?

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
        <#code#>
    }

4      

@twostraws  Site AdminHWS+

If you haven't already watched my video on this stuff, you might want to consider doing so: https://www.youtube.com/watch?v=SR7DtcT61tA

4      

@twostraws I have! Excellent video. Had some troubles with the sections so I switched back from compositional layout (I had the headers working there) to flow layout. That's where I can't get the header. But I solved it by doing it differently (no header) ...

3      

Using the SectionHeader class from Paul's video mentioned above I came up with this conversion for your code example. Would this work for you?

private func setupCollectionViewWithCompostionalLayout() {
        // Adjust width and height as needed
        let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.33), heightDimension: .fractionalHeight(0.5))
        let item = NSCollectionLayoutItem(layoutSize: itemSize)

        // Adjust height and item spacing as needed
        let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .absolute(60))
        let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item])
        group.interItemSpacing = .fixed(10)

        let section = NSCollectionLayoutSection(group: group)
        section.contentInsets = NSDirectionalEdgeInsets(top: 12, leading: 12, bottom: 12, trailing: 12)

        // This is where the header gets added:
        let headerSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .absolute(50))
        let header = NSCollectionLayoutBoundarySupplementaryItem(layoutSize: headerSize, elementKind: UICollectionView.elementKindSectionHeader, alignment: .top)
        section.boundarySupplementaryItems = [header]

        let layout = UICollectionViewCompositionalLayout(section: section)

        collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
        collectionView.register(YourCellClassHere.self, forCellWithReuseIdentifier: "cellID")
        collectionView.register(SectionHeader.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: SectionHeader.reuseIdentifier)

        view.addSubview(collectionView)

        NSLayoutConstraint.activate([
            collectionView.topAnchor.constraint(equalTo: view.topAnchor),
            collectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            collectionView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            collectionView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])
    }

3      

Thanks for taking the effort to sort this out!

3      

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