iOS Swift. How to Asynchronously Download and Cache Images

Loading an Image Asynchronously

Download image from Internet using URLSession and its dataTask method. Image will be loaded asynchronously and set as image of  UIImageView in main UI thread using DispatchQueue.main.async.

import UIKit

class SingleImageViewController: UIViewController {
    
    @IBOutlet var imageView: UIImageView!
    
    let urlStr = "https://cdn.pixabay.com/photo/2017/05/07/08/56/pancakes-2291908_960_720.jpg"

    override func viewDidLoad() {
        super.viewDidLoad()
        
        imageView.contentMode = .scaleAspectFill
        imageView.clipsToBounds = true
        
        if let url = URL(string: urlStr) {
            let session = URLSession.shared
            let dataTask = session.dataTask(with: url) { (data, response, error) in
                if let unwrappedError = error {
                    print(unwrappedError)
                    return
                }
                
                if let unwrappedData = data {
                    let image = UIImage(data: unwrappedData)
                    DispatchQueue.main.async(execute: {
                        self.imageView.image = image
                    })
                }
                
            }
            dataTask.resume()
        }
    }

}

Display downloaded image