Modified image view that can cache and download images, first it will try fetch the image from cache if couldn't found it will download from the given url

CachableImageView.swift

//
//  CachableImageView.swift
//  Test
//
//  Created by Coder ACJHP on 26.10.2018.
//  Copyright © 2018 Coder ACJHP. All rights reserved.
//

import UIKit

// This extension allow us to download image from the url
let imageCache = NSCache<AnyObject, AnyObject>()

class CachableImageView: UIImageView {
    
    var imageUrlString: String?
    
    func loadImageUsingUrlString(urlString: String) {
        let url = URL(string: urlString)!
        
        self.image = nil
        
        // If image already stored in cache assing it to image
        if let imageFromCache = imageCache.object(forKey: urlString as AnyObject) as? UIImage {
            self.image = imageFromCache
            return
        }
        
        // Download the image and store it in cache
        URLSession.shared.dataTask(with: url) { (data, response, error) in
            
            if error != nil {
                print(error!.localizedDescription)
                return
            }
            DispatchQueue.main.async {
                
                let imageToCache = UIImage(data: data!)
                
                if self.imageUrlString == urlString {
                    self.image = imageToCache
                }
                imageCache.setObject(imageToCache!, forKey: urlString as AnyObject)
            }
        }.resume()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
}