Preload Collection View (So that scrolling is smooth) - ios

Question

I would like to be able to preload the items in my collection view when it is being scrolled up and down.
I am using the data of two arrays to load the data in the collection view:
(1) availableLabelNames: [String]
(2) availableImageNames: [String]
Collection View functions in AvailableImages:
class availableImages: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource
{
#IBOutlet weak var searchBar: UISearchBar!
#IBOutlet weak var collectionView: UICollectionView!
public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
{
return availableLabelNames.count
}
public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
{
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "customCell", for: indexPath) as! CustomCollectionViewCell
cell.borderFolder.layer.borderColor = UIColor.black.cgColor
cell.borderFolder.layer.borderWidth = 2
cell.borderFolder.layer.cornerRadius = 5
cell.squareDesign.layer.cornerRadius = 5
let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(availableImages.connected(_:)))
cell.imageCell.isUserInteractionEnabled = true
cell.imageCell.tag = indexPath.row
cell.imageCell.addGestureRecognizer(tapGestureRecognizer)
//setting image
cell.imageCell.image = UIImage(named: availableImageNames[indexPath.row])
//setting label
cell.labelName.text = availableLabelNames[indexPath.row]
return cell
}
}
Custom collection view class:
import UIKit
protocol Normal: class
{
func delete (cell: CustomCollectionViewCell)
func pressed (cell: CustomCollectionViewCell)
func textChanged (cell: CustomCollectionViewCell)
func finishedEditing (cell: CustomCollectionViewCell)
func textStartedEditing (cell: CustomCollectionViewCell)
}
class CustomCollectionViewCell: UICollectionViewCell
{
#IBOutlet weak var imageCell: UIImageView!
#IBOutlet weak var deleteButton: UIButton!
#IBOutlet weak var cellButton: UIButton!
#IBOutlet weak var labelName: UILabel!
#IBOutlet weak var textFieldName: UITextField!
#IBOutlet weak var squareDesign: UIView!
#IBOutlet weak var borderFolder: UIView!
weak var delegate: Normal?
//...class goes on but not important
Please could someone help me I have looked everywhere but nothing seems to work or makes sense in terms of my application.
Thank you so much! :)

Answer 1

Collection view is doing preloading by default. Your problem is elsewhere, you can't do heavy work in cell for item.
Would need a sample project to try it on, but I would bet this is the root of the problem:
cell.imageCell.image = UIImage(named: availableImageNames[indexPath.row])
rewrite it to this:
DispatchQueue.main.async { [weak self] in
guard let weakSelf = self else { return }
cell.imageCell.image = UIImage(named: weakSelf.availableImageNames[indexPath.row])
}
Also, as cells are reused, you want to reset their image. Otherwise, images will be shown randomly.