UICollectionView not obeying UICollectionViewDelegateFlowLayout and insets - ios

Question

So I have a CollectionView that has the following code:
class MyViewController: UIViewController {
...
#IBOutlet weak var imageCollectionView: UICollectionView!
fileprivate let sectionInsets = UIEdgeInsets(top: 1, left: 1, bottom: 1, right: 1)
fileprivate let itemsPerRow: CGFloat = 3
...
override func viewDidLoad() {
super.viewDidLoad()
imageCollectionView.delegate = self
imageCollectionView.dataSource = self
}
}
...
extension MyViewController : UICollectionViewDelegateFlowLayout {
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
sizeForItemAt indexPath: IndexPath) -> CGSize {
let paddingSpace = sectionInsets.left * (itemsPerRow + 1)
let availableWidth = collectionView.bounds.width - paddingSpace
let widthPerItem = availableWidth / itemsPerRow
return CGSize(width: widthPerItem, height: widthPerItem)
}
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
insetForSectionAt section: Int) -> UIEdgeInsets {
return sectionInsets
}
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return sectionInsets.left
}
}
What I'm going for is 3 cells per row with very little space between but whenever I run the app I get something like this:
Where each black block is a cell.
For similar questions I've found, the answer is usually to implement the UICollectionViewDelegateFlowLayout functions which I've done and my functions are being called but just not working as expected! Even if I manually change the widthPerItem value to be slightly smaller, it still doesn't work!
Can anyone see if I'm missing something obvious here?
Thank you!

Answer 1

Did you make sure the minimum inter-item spacing is set to only 1 point?
You can set this up in Interface Builder or by overriding the following delegate method:
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
return 1.0;
}
Another possible reason I see is that the result of dividing availableWidth by itemsPerRow is a floating number. In the end the sum of the cell widths and the inset and might actually exceed the collection view width by 0.x pixels. To make sure this doesn't happen, you may want to use floor:
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
sizeForItemAt indexPath: IndexPath) -> CGSize {
let paddingSpace = sectionInsets.left * (itemsPerRow + 1)
let availableWidth = collectionView.bounds.width - paddingSpace
let widthPerItem = floor(availableWidth / itemsPerRow)
return CGSize(width: widthPerItem, height: widthPerItem)
}