Allows a user to download an image asynchronously directly into a UIImageView and cache it

UIImageView+asyncCache.swift

//
//  UIImageView+asyncCache.swift
//
//  Created by Zhendryk on 10/18/18.
//  Copyright © 2018 Zhendryk. All rights reserved.

import Foundation
import UIKit

let imageCache = NSCache<NSString, UIImage>()

extension UIImageView {
    
    func getImageFrom(urlString: String?, contentMode: UIView.ContentMode = .scaleAspectFit, placeholder: UIImage? = nil) {
        
        if urlString == nil {
            self.image = placeholder
            return
        }
        
        self.image = placeholder
        self.contentMode = contentMode
        if let cachedImage = imageCache.object(forKey: NSString(string: urlString!)) {
            self.image = cachedImage
            return
        }
        
        if let url = URL(string: urlString!) {
            URLSession.shared.dataTask(with: url) { (data, response, error) in
                if let error = error {
                    AppUtil.debugLog(file: #file, function: #function, line: #line, error)
                    DispatchQueue.main.async {
                        self.image = placeholder
                    }
                    return
                }
                DispatchQueue.main.async {
                    if let data = data {
                        if let downloadedImage = UIImage(data: data) {
                            imageCache.setObject(downloadedImage, forKey: NSString(string: urlString!))
                            self.image = downloadedImage
                            self.layoutSubviews()
                        }
                    }
                }
            }.resume()
        }
    }
}