still got space when I set minSpace to 0 CollectionView cell - ios

Question

I now have a collectionView with 4 cells per row.
I've set layout like the following
let width = UIScreen.main.bounds.width / 4
let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
layout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
layout.itemSize = CGSize(width: width, height: width)
layout.minimumInteritemSpacing = 0
layout.minimumLineSpacing = 0
self.module_CollectionView.collectionViewLayout = layout
which should give me a collectionView without any spacing between cells.
However, I still got very thin (looks like 1px) space between columns.
(please refer to the screen shot below)
It works fine if the cell width is 1/5 or 1/3 of Screen width.
I guess it's because the remainder or something ?
Would be good if someone could point out what might goes wrong.
thanks.

Answer 1

I think you might set wrong constraint, otherwise nothing is wrong in your code for flowlayout.
Now, first take one UIView in your collectionviewcell and set it's four constraint - top.leading,trailing,bottom with constant 0.
Then add your all the stuff (your views or images or buttons) in that view and give proper constraint.

Answer 2

You need to implement collectionView(_ collectionView: UICollectionView, layout collectionViewLayout:UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize.
In your case, the screen width is 375, and you want to divides it to 4 parts. If you directly divides 375 to 4 parts, you'll get 93.75, with decimal.
You should round it(decimal) to an integer like 94 + 94 + 94 + 93 = 375 instead of 93.75+93.75+93.75+93.75 = 375.
For Example:
override func viewDidLoad() {
super.viewDidLoad()
let screenWidth:Int = UIScreen.main.bounds.width
let parts:CGFloat = 4
var rounding:Int = 0
if(screenWidth.truncatingRemainder(dividingBy: parts) != 0) {
rounding = Int(screenWidth.truncatingRemainder(dividingBy: parts))
}
}
//----
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
var roundingWidth = 0
if(rounding != 0) {
rounding -= 1
roundingWidth = 1
}
return CGSize(width: Int(screenWidth / parts) + roundingWidth, height: yourHeight)
}