CollectionView reloadItems(at: ) calls didSet() in multiple cells - ios

Question

I'm working on an app that has a UICollectionView with an infinite scroll. Each cell has a like button. The problem is that the lower I scroll - the slower the like button changes its color when tapped on.
It can take up to 3 seconds between the print("BEGIN") and print("END") in my code. I also observed that print(post) gets called dozens of times and it prints dozens of posts that I haven't tapped the like button on. I want it to only call the didSet in the cell I'm updating.
Can someone please explain why it seems like it's calling didSet in multiple cells instead of just one cell I tapped on? Does it have something to do with that cells are being reused?
How would you fix this long delay problem? I would like the cell to update it's like button image to a selected one without such a long delay.
protocol HomePostCellDelegate {
func didTapLike(for cell: HomePostCell)
}
class HomePostCell: UICollectionViewCell {
var delegate: HomePostCellDelegate?
var post: Post? {
didSet {
print(post)
likeButton.setImage(post?.isLiked == true ? #imageLiteral(resourceName: "like_selected").withRenderingMode(.alwaysTemplate) : #imageLiteral(resourceName: "like_unselected").withRenderingMode(.alwaysTemplate), for: .normal)
likeButton.tintColor = .white
// ...
}
}
lazy var likeButton: UIButton = {
let button = UIButton(type: .system)
button.setImage(#imageLiteral(resourceName: "like_unselected").withRenderingMode(.alwaysOriginal), for: .normal)
button.addTarget(self, action: #selector(handleLike), for: .touchUpInside)
return button
}()
#objc func handleLike() {
NSLog("#objc func handleLike()")
delegate?.didTapLike(for: self)
}
// ...
}
class HomeController: UICollectionViewController, UICollectionViewDelegateFlowLayout, HomePostCellDelegate {
// ...
func didTapLike(for cell: HomePostCell) {
let generator = UIImpactFeedbackGenerator(style: .light)
generator.impactOccurred()
guard let indexPath = collectionView?.indexPath(for: cell) else { return }
guard let post = cell.post else { return }
cell.post.isLiked = !cell.post.isLiked
if cell.post.isLiked {
cell.post.numberOfLikes += 1
} else {
cell.post.numberOfLikes -= 1
}
print("BEGIN")
self.collectionView?.reloadItems(at: [indexPath])
print("END")
}
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if indexPath.item == self.presenter.posts.count - 5 && !presenter.isFinishedPaging && !presenter.isCurrentlyPaging {
presenter.isCurrentlyPaging = true
presenter.paginatePosts(withSuccess: { [weak self] () in
self?.collectionView?.refreshControl?.endRefreshing()
self?.collectionView?.reloadData()
self?.presenter.isCurrentlyPaging = false
}) { [weak self] (errorMessage) in
self?.presenter.isCurrentlyPaging = false
print(errorMessage)
}
}
if presenter.posts.count == 0 {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: errorCellId, for: indexPath) as! ErrorCell
setUpErrorCellAnimation(cell: cell)
return cell
} else if presenter.posts[indexPath.item].id == nil {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: adCellId, for: indexPath) as! AdCell
// some ad logic here
// ...
cell.contentView.addSubview(bannerView)
return cell
} else {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! HomePostCell
cell.delegate = self
if presenter.isAdmin && presenter.isInAdminView {
cell.isInAdminView = true
} else {
cell.isInAdminView = false
}
cell.post = presenter.posts[safe: indexPath.item]
return cell
}
}
UPDATE:
Stack trace when putting a breakpoint inside the didSet method: