get the actual UICollectionView item spacing - ios

Question

how can I get the actual interItemSpacing for a horizontal flow layout in the UICollectionView ? the only info I can get (and set) is minimumInteritemSpacing.
I need it for the sake of the following small calculation to always display 3 equally width items in the collection view regardless to screen size (i want to replace minimumInteritemSpacing with the current value of interItemSpacing in the formula):
flowLayout.itemSize = CGSizeMake((_collectionView.frame.size.width/3.0)-(flowLayout.minimumInteritemSpacing/3.0), _collectionView.frame.size.height); I put this calculation in viewDidLayoutSubviews and it's not working precisely for some screens because their current interItemSpacing is different than the minimumInteritemSpacing
thanks in advance.

Answer 1

You could get the actual spacing by comparing two sequential cells
Something like
let firstIndex = IndexPath(item: 0, section: 0)
let secondIndex = IndexPath(item: 1, section: 0)
if let att1 = collectionView.layoutAttributesForItem(at: firstIndex),
let att2 = collectionView.layoutAttributesForItem(at: secondIndex) {
let actualSpace = att2.frame.minX - att1.frame.maxX
print (actualSpace)
}

Answer 2

For creating cells with fixing spacing try this:
private let minItemSpacing: CGFloat = 8
private let itemWidth: CGFloat = 100
private let headerHeight: CGFloat = 32
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
// Create our custom flow layout that evenly space out the items, and have them in the center
let layout = UICollectionViewFlowLayout()
layout.itemSize = CGSize(width: itemWidth, height: itemWidth)
layout.minimumInteritemSpacing = minItemSpacing
layout.minimumLineSpacing = minItemSpacing
layout.headerReferenceSize = CGSize(width: 0, height: headerHeight)
// Find n, where n is the number of item that can fit into the collection view
var n: CGFloat = 1
let containerWidth = collectionView.bounds.width
while true {
let nextN = n + 1
let totalWidth = (nextN*itemWidth) + (nextN-1)*minItemSpacing
if totalWidth > containerWidth {
break
} else {
n = nextN
}
}
// Calculate the section inset for left and right.
// Setting this section inset will manipulate the items such that they will all be aligned horizontally center.
let inset = max(minItemSpacing, floor( (containerWidth - (n*itemWidth) - (n-1)*minItemSpacing) / 2 ) )
layout.sectionInset = UIEdgeInsets(top: minItemSpacing, left: inset, bottom: minItemSpacing, right: inset)
collectionView.collectionViewLayout = layout
}
For more information, this excellent article:
http://samwize.com/2015/11/30/understanding-uicollection-flow-layout/