iOS Swift

Circle shaped collection view layout on iOS

UICollectionViewLayout’s responsibility is to define layout: all the cell locations and sizes. It acts like a data source object which provides layout related information to the collection view. Collection view then uses that information for creating cells and placing them on screen. This time we’ll take a look on how to create a custom circle shaped layout.

Creating UICollectionViewLayout subclass

First step for creating a custom layout is to create UICollectionViewLayout subclass. Then we need to define the size of the layout. In this simple case, all the cells will fit into the available area – therefore we can just return the collection view’s own size.

override var collectionViewContentSize: CGSize {
return collectionView?.bounds.size ?? .zero

When-ever user rotates the device, the size of the collection view changes, therefore we would like to reset the layout.

override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
return true

Prepare is called whenever layout gets invalidated and it is a best place where to pre-calculate cell locations. Then it is possible to return attributes in all of the other methods querying for attributes later on. This gives us the best possible performance.

Items are placed along a circle which is centred in the collection view. As collection view can be under navigation bar, then the frame of the circle needs to take account contentOffset. Moreover, as centre points of items are on the circle, we also need to take account the item size. Calculating positions for items is just a matter of applying simple trigonometry with right-angled triangles.

private var layoutCircleFrame =
private let layoutInsets = UIEdgeInsets(top: 8, left: 8, bottom: 8, right: 8)
private let itemSize = CGSize(width: 100, height: 100)
private var itemLayoutAttributes = [UICollectionViewLayoutAttributes]()
override func prepare() {
guard let collectionView = collectionView else { return }
layoutCircleFrame = CGRect(origin: .zero, size: collectionViewContentSize)
.inset(by: layoutInsets)
.insetBy(dx: itemSize.width / 2.0, dy: itemSize.height / 2.0)
.offsetBy(dx: collectionView.contentOffset.x, dy: collectionView.contentOffset.y)
.insetBy(dx: collectionView.contentOffset.x, dy: collectionView.contentOffset.y)
for section in 0..<collectionView.numberOfSections {
switch section {
case 0:
let itemCount = collectionView.numberOfItems(inSection: section)
itemLayoutAttributes = (0..<itemCount).map({ (index) -> UICollectionViewLayoutAttributes in
let angleStep: CGFloat = 2.0 * CGFloat.pi / CGFloat(itemCount)
// CGRect extension for center and innerRadius:
var position =
position.x += layoutCircleFrame.size.innerRadius * cos(angleStep * CGFloat(index))
position.y += layoutCircleFrame.size.innerRadius * sin(angleStep * CGFloat(index))
let indexPath = IndexPath(item: index, section: section)
let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
attributes.frame = CGRect(center: position, size: itemSize)
return attributes
fatalError("Unhandled section \(section).")

If we have pre-calculated attributes, then it is straight-forward to return them in the layout attributes methods. When adding or removing items, cells will move to new location with a nice animation by default.

override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
return itemLayoutAttributes
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
let numberOfItems = collectionView?.numberOfItems(inSection: indexPath.section) ?? 0
guard numberOfItems > 0 else { return nil }
switch indexPath.section {
case 0:
return itemLayoutAttributes[indexPath.item]
fatalError("Unknown section \(indexPath.section).")

I would like to highlight the fact that content presented here is just a bare minimum for setting up custom collection view layout. UICollectionView is highly configurable.

Setting up collection view

When custom collection view layout is ready, it is time to hook it up to the collection view. Custom collection view layout can be set in storyboard or when initialising collection view or collection view controller.

Setting custom layout in UIStoryBoard

Implementing a basic collection view controller for just showing one type of cells requires only a little bit of code. Data source methods provide the count of the items and sections and return configured collection view cells.

final class CollectionViewController: UICollectionViewController {
// MARK: Managing the View
enum ReuseIdentifier: String {
case item = "ItemCell"
override func viewDidLoad() {
collectionView!.register(CircleCollectionViewCell.self, forCellWithReuseIdentifier: ReuseIdentifier.item.rawValue)
navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(addItem))
// MARK: Managing the Content
private var items: [UIColor] = [.random(), .random(), .random()]
@objc private func addItem() {
collectionView.insertItems(at: [IndexPath(item: items.count 1, section: 0)])
// MARK: Collection View Data Source
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return items.count > 0 ? 1 : 0
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return items.count
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: ReuseIdentifier.item.rawValue, for: indexPath) as! CircleCollectionViewCell
cell.backgroundView?.backgroundColor = items[indexPath.item]
cell.titleLabel.text = "\(indexPath.item)"
return cell


Adding custom collection view layout requires subclassing UICollectionViewLayout and overriding several methods. The core idea is to provide UICollectionViewAttributes for every cell which UICollectionView will then use for creating and laying out cells.

If this was helpful, please let me know on Mastodon@toomasvahter or Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.

Example project

CustomCollectionViewLayout (GitHub), Xcode 10.1, Swift 4.2


5 replies on “Circle shaped collection view layout on iOS”

There is a error on this line:
position.x += layoutCircleFrame.size.innerRadius * cos(angleStep * CGFloat(index))

Error: Value of type ‘CGSize’ has no member ‘innerRadius’


I got the solution from you:
extension CGRect {
init(center: CGPoint, size: CGSize) {
self.init(x: center.x – size.width / 2.0, y: center.y – size.height / 2.0, width: size.width, height: size.height)

var center: CGPoint { return CGPoint(x: midX, y: midY) }

extension CGSize {
var innerRadius: CGFloat { return min(width, height) / 2.0 }

Thanks a lot!


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s