Changing UICollectionview cell XY position - swift 3 - ios

Question

I'm using a UICollectionview with XX cells. How can i change the XY position on every single cell programmatically? I can change the size of every cell with:
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize
Is there another function like above that changes the XY positioning?

Answer 1

I hope this example will help you. Let me explain this code blocks. You can think standard UICollectionView and Cell design. There is no detailView. This code implementation will create parallax effect HeaderView.
FIRST AND FOREMOST
import UIKit
class DIYLayoutAttributes: UICollectionViewLayoutAttributes {
var deltaY: CGFloat = 0
override func copy(with zone: NSZone?) -> Any {
let copy = super.copy(with: zone) as! DIYLayoutAttributes
copy.deltaY = deltaY
return copy
}
override func isEqual(_ object: Any?) -> Bool {
if let attributes = object as? DIYLayoutAttributes {
if attributes.deltaY == deltaY {
return super.isEqual(object)
}
}
return false
}
}
class DIYLayout: UICollectionViewFlowLayout {
var maximumStretchHeight: CGFloat = 0
override class var layoutAttributesClass : AnyClass {
return DIYLayoutAttributes.self
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
// Create layout attributes
let layoutAttributes = super.layoutAttributesForElements(in: rect) as! [DIYLayoutAttributes]
// How far user scrollview.
let insets = collectionView!.contentInset
let offset = collectionView!.contentOffset
let minY = -insets.top
// we need the calculate delta.
if (offset.y < minY) {
let deltaY = fabs(offset.y - minY)
// we can loop through all attributes
for attributes in layoutAttributes {
//Manipulate attributes
if let elementKind = attributes.representedElementKind {
if elementKind == UICollectionElementKindSectionHeader {
// create frame.
var frame = attributes.frame
frame.size.height = max(minY, headerReferenceSize.height + deltaY)
//We need the change origin for scrolling.
frame.origin.y = frame.minY - deltaY
attributes.frame = frame
attributes.deltaY = deltaY
}
}
}
}
return layoutAttributes
}
// Layout will scroll.
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
return true
}
SECOND
You need custom cell design.
import UIKit
class ScheduleHeaderView: UICollectionReusableView {
#IBOutlet fileprivate weak var backgroundImageView: UIView!
#IBOutlet fileprivate weak var backgroundImageViewHeightLayoutConstraint: NSLayoutConstraint!
#IBOutlet fileprivate weak var foregroundImageView: UIView!
#IBOutlet fileprivate weak var foregroundImageViewHeightLayoutConstraint: NSLayoutConstraint!
fileprivate var backgroundImageViewHeight: CGFloat = 0
fileprivate var foregroundImageViewHeight: CGFloat = 0
fileprivate var previousHeight: CGFloat = 0
override func awakeFromNib() {
super.awakeFromNib()
backgroundImageViewHeight = backgroundImageView.bounds.height
foregroundImageViewHeight = foregroundImageView.bounds.height
}
override func apply(_ layoutAttributes: UICollectionViewLayoutAttributes) {
super.apply(layoutAttributes)
let attributes = layoutAttributes as! DIYLayoutAttributes
let height = attributes.frame.height
if previousHeight != height {
backgroundImageViewHeightLayoutConstraint.constant = backgroundImageViewHeight - attributes.deltaY
foregroundImageViewHeightLayoutConstraint.constant = foregroundImageViewHeight + attributes.deltaY
previousHeight = height
}
}
}
THIRD
override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: "ScheduleHeader", for: indexPath) as! ScheduleHeaderView
return header
}
Of course we need to from viewDidLoad.
override func viewDidLoad() {
super.viewDidLoad()
//Add layout.
let width = collectionView!.bounds.width
let layout = collectionViewLayout as! DIYLayout
layout.headerReferenceSize = CGSize(width: width, height: 180)
layout.itemSize = CGSize(width: width, height: 62)
layout.maximumStretchHeight = width
}