UICollectionView - Downloading images and effective reloading of data, like Instagram

Question

I noticed that apps like Intagram uses UICollectionViews to display the feed of photos. I also noticed that the cells for these photos is somehow placed on screen

Answer 1

Use following to load image Async in cell in cellForItemAtIndexPath delegate method

let url = URL(string: productModel.productImage)

    let data = try? Data(contentsOf: url!)
    DispatchQueue.main.async(execute: {
        collectionViewCell.imageView.image = UIImage(data: data!)
    });

Implement protocol "UICollectionViewDataSourcePrefetching" in you ViewController as

class ViewController: UIViewController , UICollectionViewDataSourcePrefetching {

Set following delegates to your collection view in storyboard (see the attached image) or programmatically

In ViewController's viewDidLoad method

collectionView.delegate = self
collectionView.dataSource = self
collectionView.prefetchDataSource = self