Yes, I've checked other questions regarding this topic. For some reason, the function
override func scrollViewDidScroll(_ scrollView: UIScrollView) {
print(scrollView.contentOffset)
}
is not called inside my UICollectionView class.
Here is the full class. I basically want to update my pageControl when user swipes on each cell.
I tried collectionView:willDisplayCell:forItemAtIndexPath:
method but i found that sometimes when I scroll and stop midway the cell and come back, it is not updating to the previous value. Hence why i resorted to the scrollview delegate.
class FilterInfoImagesCollectionViewController: UICollectionViewController {
var selectedFilterCollection: FilterCollection!
private let pageControl: UIPageControl = {
let pageControl = UIPageControl()
pageControl.currentPage = 0
pageControl.numberOfPages = 5 // Hardcoded since we know there will only be 5 example images
pageControl.translatesAutoresizingMaskIntoConstraints = false
return pageControl
}()
private var datasource: DataSource!
private var datas = [FilterInfo]()
override func viewDidLoad() {
super.viewDidLoad()
collectionView.alwaysBounceVertical = false
collectionView.isPagingEnabled = true
collectionView.register(FilterInfoCollectionViewCell.self, forCellWithReuseIdentifier: FilterInfoCollectionViewCell.ReuseIdentifier)
collectionView.collectionViewLayout = createLayout()
collectionView.backgroundColor = .clear
collectionView.delegate = self
collectionView.dataSource = self
configureDatasource()
setupDatas()
setupView()
setupConstraint()
}
private func setupDatas() {
let filterName = selectedFilterCollection.name.components(separatedBy: " ").first!
for n in 1 ... 5 {
let image = UIImage(named: "\(filterName).ex\(n)")
let filterInfo = FilterInfo(image: image, filterName: "\(filterName)\(n)")
datas.append(filterInfo)
}
self.createSnapshot(from: datas)
}
private func setupView() {
self.view.addSubview(pageControl)
}
private func setupConstraint() {
pageControl.snp.makeConstraints { (make) in
make.centerX.equalToSuperview()
make.bottom.equalToSuperview()
}
}
}
extension FilterInfoImagesCollectionViewController {
fileprivate enum Section { case main }
fileprivate typealias DataSource = UICollectionViewDiffableDataSource<Section, FilterInfo>
fileprivate typealias Snapshot = NSDiffableDataSourceSnapshot<Section, FilterInfo>
fileprivate func configureDatasource() {
datasource = DataSource(collectionView: collectionView!, cellProvider: { (collectionView, indexPath, filterInfo) -> UICollectionViewCell? in
guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: FilterInfoCollectionViewCell.ReuseIdentifier, for: indexPath) as? FilterInfoCollectionViewCell else { return nil }
cell.filterInfo = filterInfo
return cell
})
}
fileprivate func createSnapshot(from datas: [FilterInfo]) {
var snapshot = Snapshot()
snapshot.appendSections([.main])
snapshot.appendItems(datas)
datasource.apply(snapshot, animatingDifferences: true)
}
private func createLayout() -> UICollectionViewLayout {
let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1))
let item = NSCollectionLayoutItem(layoutSize: itemSize)
let groupSize = NSCollectionLayoutSize(
widthDimension: .fractionalWidth(1),
heightDimension: .fractionalHeight(1))
let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitem: item, count: 1)
let section = NSCollectionLayoutSection(group: group)
section.orthogonalScrollingBehavior = .groupPaging
let layout = UICollectionViewCompositionalLayout(section: section)
return layout
}
}
extension FilterInfoImagesCollectionViewController {
override func scrollViewDidScroll(_ scrollView: UIScrollView) {
print(scrollView.contentOffset)
}
}
How come it is not called? I tried to check with other scrollview delegate methods and the same thing happen - not called.
UPDATE: Added delegate and datasource to self as per request
Add in viewDidLoad. scroll function related to UICollectionViewDelegate and you need to set the delegate for using your override functions
section.visibleItemsInvalidationHandler = { [weak self] visibleItems, point, environment in
self?.pager.currentPage = visibleItems.last!.indexPath.row
}