cellForItemAt called only once in Swift collectionView - ios

Question

If I use flow layout with collectionView, then all my cells are visible with the data. If I use a custom layout, then cellForItemAt is only accessed for index (0,0), and correspondingly only a single cell is displayed.
I'm baffled why - please help!
Minimal example below:
ViewController:
import UIKit
private let reuseIdentifier = "customCell"
class customCollectionViewController: UICollectionViewController {
#IBOutlet var customCollectionView: UICollectionView!
let dwarfArray = ["dopey", "sneezy", "bashful", "grumpy", "doc", "happy", "sleepy"]
override func viewDidLoad() {
super.viewDidLoad()
}
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return dwarfArray.count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! customCollectionViewCell
let cellContentsIndex = indexPath.row
if cellContentsIndex <= dwarfArray.count
{
cell.displayContent(name: dwarfArray[cellContentsIndex])
}
return cell
}
}
Custom Cell
import UIKit
class customCollectionViewCell: UICollectionViewCell {
#IBOutlet weak var nameLabel: UILabel!
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setup()
}
override init(frame: CGRect){
super.init(frame: frame)
}
public func displayContent(name: String){
nameLabel.text = name
}
func setup(){
self.layer.borderWidth = 1.0
self.layer.borderColor = UIColor.black.cgColor
}}
Custom Layout
If this is not here - I can see all the cells I expect (albeit without my preferred layout). When I use this, I only see one cell.
import UIKit
class customCollectionViewLayout: UICollectionViewLayout {
let CELL_SIZE = 100.0
var cellAttrsDictionary = Dictionary<NSIndexPath, UICollectionViewLayoutAttributes>()
//define the size of the area the user can move around in within the collection view
var contentSize = CGSize.zero
var dataSourceDidUpdate = true
func collectionViewContentSize() -> CGSize{
return self.contentSize
}
override func prepare() {
if (collectionView?.numberOfItems(inSection: 0))! > 0 {
/// cycle through each item of the section
for item in 0...(collectionView?.numberOfItems(inSection: 0))!-1{
/// build the collection attributes
let cellIndex = NSIndexPath(item: item, section: 0)
let xPos = Double(item)*CELL_SIZE
let yPos = 40.0
let cellAttributes = UICollectionViewLayoutAttributes(forCellWith: cellIndex as IndexPath)
cellAttributes.frame = CGRect(x: xPos, y:yPos, width: CELL_SIZE, height: CELL_SIZE)
// cellAttributes.frame = CGRect(x: xPos, y:yPos, width: CELL_WIDTH + 2*CELL_SPACING, height: CELL_HEIGHT)
cellAttributes.zIndex = 1
//save
cellAttrsDictionary[cellIndex] = cellAttributes
}
}
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
/// create array to hold all the elements in our current view
var attributesInRTect = [UICollectionViewLayoutAttributes]()
/// check each element to see if they should be returned
for cellAttributes in cellAttrsDictionary.values {
if rect.intersects(cellAttributes.frame)
{
attributesInRTect.append(cellAttributes)
}
}
return attributesInRTect
}
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
return cellAttrsDictionary[indexPath as NSIndexPath]!
}
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
return true
}}
Output

Answer 1

The problem is with contentSize value
func collectionViewContentSize() -> CGSize{
return self.contentSize
}
Just replace func collectionViewContentSize()... by something like this:
func lastLayoutAttributes() -> UICollectionViewLayoutAttributes? {
return cellAttrsDictionary.values.map { $0 }.sorted(by: { $0.frame.maxX < $1.frame.maxX }).last
}
override var collectionViewContentSize: CGSize {
guard let collectionView = collectionView else { return .zero }
guard collectionView.frame != .zero else { return .zero }
let width: CGFloat
let height: CGFloat = collectionView.frame.height
if let lastLayoutAttributes = lastLayoutAttributes() {
width = lastLayoutAttributes.frame.maxX
} else {
width = 0
}
return CGSize(width: width, height: height)
}
And you will see more than one cell.