Items in UICollectionView disappeared on scrolling - ios

Question

I have an UICollectionViewController which will be displayed both on its own full screen mode as well as in a pop-up view of another controller. The full screen mode works perfectly. However, in the pop-up mode, all items disappears after the user scroll the content up and down for a few times (sometimes more than 10 times, but also happen at the first or second time)
let vc = storyboard.instantiateViewController(
withIdentifier: "myCollectionView") as? MyColle ctionViewController
// set up the overlap in the parent controller
let bounds = CGRect(x: x + 22, y: parentFrame.origin.y + dy,
width: width, height: parentFrame.height - dy - 10)
overlayView = UIView(frame: bounds)
overlayView!.layer.cornerRadius = 5.0
overlayView!.backgroundColor = UIColor(red: 0.8, green: 0.8, blue: 0.8, alpha: 0.4)
self.view.addSubview(overlayView!)
vc.showAsPopup(overlayView!)
// in MyCollectionViewController, add itself to the parent popup view
func showAsPopup(_ parentView: UIView) {
view.backgroundColor = UIColor.red // test color to show the view is never gone
view.layer.cornerRadius = 5.0
collectionView?.backgroundColor = UIColor.clear
collectionView?.layer.cornerRadius = 5.0
parentView.addSubview(view)
view.frame = CGRect(x: 0, y: 20,
width: parentView.frame.width,
height: parentView.frame.height - 20)
NSLog("my view bounds after: \(view.frame.origin.x) \(view.frame.origin.y)")
NSLog(" : \(view.frame.width)x\(view.frame.height)")
}
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView,
numberOfItemsInSection section: Int) -> Int {
NSLog("\(items.count) items in section \(section)")
return items.count
}
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
sizeForItemAt indexPath: IndexPath) -> CGSize {
let screenRect = view.bounds
let scale = UIScreen.main.scale
let width = screenRect.size.width - 20
return CGSize(width: width, height: 45 * scale)
}
override func collectionView(_ collectionView: UICollectionView,
cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let item = items[indexPath.item]
let cellId = "RCCell_\(item.id)"
NSLog("creating cell \(cellId)")
// Register cell classes
self.collectionView!.register(RemoteControlViewCell.self,
forCellWithReuseIdentifier: cellId)
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId,
for: indexPath) as! RemoteControlViewCell
// Configure the cell, override the icon in Cell
cell.itemId = item.id
cell.itemIcon.image = item.icon
cell.itemDescriptionLabel.text = item.description
return cell
}
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
insetForSectionAt section: Int) -> UIEdgeInsets {
return UIEdgeInsets(top: 12.5, left: 0, bottom: 12.5, right: 0)
}
override func collectionView(_ collectionView: UICollectionView,
didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
NSLog("removed cell at \(indexPath.row)")
}
// MyCollectionViewCell
override init(frame: CGRect) {
super.init(frame: frame)
let scale = UIScreen.main.scale
NSLog("Cell frame w: \(frame.size.width) h: \(frame.size.height), scale \(scale)")
let spacing = CGFloat(10)
contentView.backgroundColor = UIColor.white
contentView.layer.cornerRadius = 5
contentView.layer.masksToBounds = true
itemIcon = UIImageView(frame: CGRect(x: spacing, y: spacing,
width: CGFloat(24.0), height: CGFloat(24.0)))
itemIcon.contentMode = UIViewContentMode.scaleAspectFit
contentView.addSubview(itemIcon)
NSLog("icon w: \(itemIcon.frame.size.width)")
let labelX = spacing + 5 + itemIcon.frame.size.width
let font = UIFont.systemFont(ofSize: 20)
itemDescriptionLabel = UILabel(
frame: CGRect(x: labelX, y: spacing,
width: frame.size.width - labelX - spacing,
height: font.lineHeight))
itemDescriptionLabel.textColor = UIColor(colorLiteralRed: 0x66 / 255.0, green: 0x66 / 255.0, blue: 0x66 / 255.0, alpha: 1.0)
moduleDescriptionLabel.font = font
contentView.addSubview(itemDescriptionLabel)
NSLog("item desc \(String(describing: itemDescriptionLabel.text)) w: \(itemDescriptionLabel.frame.size.width)")
}
I tried changing the background color of the collectionView to visible and can see that the collect view itself was never gone even though the items disappeared. I also added logging to the collectionView() callback methods and found that they were never called again after the initial view presentation.
What could cause the items to disappear during scrolling?

Answer 1

Try using prepareForReuse in RemoteControlViewCell class
override func prepareForReuse() {
itemId = ""
itemIcon.image = nil
itemDescriptionLabel.text = ""
}