1 section and 2 cells but 4 indexPath.row - swift

Question

Swift 4.
I want to return two cells in one section, so in my class CollectionViewController I do :
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1 }
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 2 }
I see two cells but if I print indexPath.row in the code below (still in the same class), I see 0 1 0 1. Why is it not only one 0 1as I have only two cells in one section ?
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! CollectionViewCell
print(indexPath.row)
return cell
}

Answer 1

cellForItemAt is getting called four times. Your numberOfItemsInSection is hard-coded for 2. When the view loads cellForItemAt is called twice (once for each cell). It is then getting called twice again when you call reloadData() from your DispatchQueue.main.async closure.
Updated - How to avoid the first call:
You need to store your cell data in an array, and only populate the array just before you call reloadData(). Thus, the array will be empty when the view is first loaded.
var yourArray = [YourObject]() //Empty Array
//..
DispatchQueue.main.async {
//append your two items to the yourArray
yourArray.append(/*cell1data*/)
yourArray.append(/*cell2data*/)
self.collectionView?.reloadData()
}
//..
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return yourArray.count
}