load image

//
//  ViewController.swift
//  MyToast
//
//  Created by hackeru on 13/11/2019.
//  Copyright © 2019 hackeru. All rights reserved.
//

import UIKit

class ViewController: UIViewController {
    let charuf="https://images.unsplash.com/photo-1484557985045-edf25e08da73?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=967&q=80"

   let neoShark="https://hips.hearstapps.com/hmg-prod.s3.amazonaws.com/images/what-is-baby-shark-1548869443.jpg?crop=0.526xw:1.00xh;0.342xw,0&resize=768:*"
    @IBOutlet weak var neoButton: UIImageView!
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

    }

    @IBAction func btnHelp(_ sender: Any) {
        //Toast.show(message: "Please help me", controller: self)
        neoButton.loadImageUsingCache(withUrl: neoShark)
    }

}

let imageCache = NSCache<NSString,UIImage>()

extension UIImageView{

    func loadImageUsingCache(withUrl urlString:String){
        let url = URL(string: urlString)
        if url == nil {return}
        self.image = nil

        //check for cached images
        if let cachedImage = imageCache.object(forKey: urlString as NSString){
            self.image = cachedImage
            return
        }

        let activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView.init(style: .gray)
        self.addSubview(activityIndicator)
        activityIndicator.startAnimating()
        activityIndicator.center = self.center

        //if not , download image from url
        URLSession.shared.dataTask(with: url!, completionHandler: {
            (data, response, error) in
            if error != nil {
                print (error!)
                return
            }
            DispatchQueue.main.async {
                if let image = UIImage(data: data!){
                    imageCache.setObject(image, forKey: urlString as NSString)
                    self.image=image
                    activityIndicator.removeFromSuperview()
                }
            }
        }).resume()

    }
}