how to implement lazy loading of images in table view using swift

Old Solution:

Since you doesn't show any code.

Here is the example for you.

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {    // try to reuse cell    let cell:CustomCell = tableView.dequeueReusableCellWithIdentifier("DealCell") as CustomCell    // get the deal image    let currentImage = deals[indexPath.row].imageID    let unwrappedImage = currentImage    var image = self.imageCache[unwrappedImage]    let imageUrl = NSURL(string: "http://staging.api.cheapeat.com.au/deals/\(unwrappedImage)/photo")    // reset reused cell image to placeholder    cell.dealImage.image = UIImage(named: "placeholder")    // async image    if image == nil {    let request: NSURLRequest = NSURLRequest(URL: imageUrl!)    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue(), completionHandler: {(response: NSURLResponse!,data: NSData!,error: NSError!) -> Void in        if error == nil {            image = UIImage(data: data)            self.imageCache[unwrappedImage] = image            dispatch_async(dispatch_get_main_queue(), {                cell.dealImage.image = image            })        }        else {        }    })    }    else{        cell.dealImage.image = image    }  return cell}

Follow THIS tutorial for more Info. Hope this will help you.

New Solution:

Here is extension for it which is created by my friend Leo Dabus which is really simple to use:

extension UIImageView {    func downloadImageFrom(link link:String, contentMode: UIViewContentMode) {        NSURLSession.sharedSession().dataTaskWithURL( NSURL(string:link)!, completionHandler: {            (data, response, error) -> Void in            dispatch_async(dispatch_get_main_queue()) {                self.contentMode =  contentMode                if let data = data { self.image = UIImage(data: data) }            }        }).resume()    }}

Now in your cellForRowAtIndexPath method assign image to cell this way:

cell.cellImageView.image = UIImage(named: "placeholder")  //set placeholder image first.cell.cellImageView.downloadImageFrom(link: imageLinkArray[indexPath.row], contentMode: UIViewContentMode.ScaleAspectFit)  //set your image from link array.

And as Rob suggested into comment here is some useful libraries which you can use:

1. https://github.com/Alamofire/AlamofireImage
2. https://github.com/onevcat/Kingfisher
3. https://github.com/rs/SDWebImage
4. https://github.com/kean/DFImageManager

Since I can't comment just yet, here's a Swift 3 (Xcode 8 Beta 6) version of the useful extension provided by Leo Dabus.

extension UIImageView {    func downloadImageFrom(link:String, contentMode: UIViewContentMode) {        URLSession.shared.dataTask( with: NSURL(string:link)! as URL, completionHandler: {            (data, response, error) -> Void in            DispatchQueue.main.async {                self.contentMode =  contentMode                if let data = data { self.image = UIImage(data: data) }            }        }).resume()    }}

I'm using this inside a class that populates the table cell, it works like this in that context just fine, just in case any newbs were wondering if it will:

albumArt.image = UIImage(named: "placeholder")albumArt.downloadImageFrom(link: "http://someurl.com/image.jpg", contentMode: UIViewContentMode.scaleAspectFit)

Details

• Xcode 10.2.1 (10E1001), Swift 5

Full sample

Info.plist (add value)

<key>NSAppTransportSecurity</key><dict>    <key>NSAllowsArbitraryLoads</key>    <true/></dict>

Podfile

target 'stackoverflow-28694645' do  # Comment the next line if you're not using Swift and don't want to use dynamic frameworks  use_frameworks!  # Pods for stackoverflow-28694645  pod 'Alamofire'  pod 'AlamofireImage'end

Code

import UIKitimport Alamofireimport AlamofireImageclass ViewController: UIViewController {    private weak var tableView: UITableView?    private var items = [ItunceItem]()    override func viewDidLoad() {        super.viewDidLoad()        let tableView = UITableView()        view.addSubview(tableView)        tableView.translatesAutoresizingMaskIntoConstraints = false        tableView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true        tableView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true        tableView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor).isActive = true        tableView.rightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.rightAnchor).isActive = true        tableView.tableFooterView = UIView()        tableView.register(TableViewCell.self, forCellReuseIdentifier: "TableViewCell")        tableView.rowHeight = 100        tableView.separatorColor = .clear        self.tableView = tableView        loadData()    }    private func loadData() {        let urlString = "https://itunes.apple.com/search?term=navigator"        Alamofire.request(urlString).response { [weak self] response in            guard let self = self, let data = response.data else { return }            do {                let decoder = JSONDecoder()                decoder.keyDecodingStrategy = .convertFromSnakeCase                self.items = try decoder.decode(ItunceItems.self, from: data).results                DispatchQueue.main.async { [weak self] in                    guard let tableView = self?.tableView else { return }                    tableView.delegate = self                    tableView.dataSource = self                    tableView.reloadData()                }            } catch let error { print("\(error.localizedDescription)") }        }    }}extension ViewController: UITableViewDataSource {    func numberOfSections(in tableView: UITableView) -> Int { return 1 }    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int { return items.count }    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {        let cell = tableView.dequeueReusableCell(withIdentifier: "TableViewCell") as! TableViewCell        return cell    }}extension ViewController: UITableViewDelegate {    func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {        guard   let cell = cell as? TableViewCell,                let imageUrlString = items[indexPath.row].artworkUrl100,                let url = URL(string: imageUrlString) else { return }        cell.photoImageView?.af_setImage(withURL: url)    }    func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) {        guard let cell = cell as? TableViewCell else { return }        cell.photoImageView?.af_cancelImageRequest()    }}struct ItunceItems: Codable { let results: [ItunceItem] }struct ItunceItem: Codable { var artworkUrl100: String? }class TableViewCell: UITableViewCell {    private(set) weak var photoImageView: UIImageView?    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {        super.init(style: style, reuseIdentifier: reuseIdentifier)        selectionStyle = .none        let imageView = UIImageView()        addSubview(imageView)        imageView.translatesAutoresizingMaskIntoConstraints = false        imageView.topAnchor.constraint(equalTo: safeAreaLayoutGuide.topAnchor, constant: 6).isActive = true        imageView.bottomAnchor.constraint(equalTo: safeAreaLayoutGuide.bottomAnchor).isActive = true        imageView.leftAnchor.constraint(equalTo: safeAreaLayoutGuide.leftAnchor).isActive = true        imageView.rightAnchor.constraint(equalTo: safeAreaLayoutGuide.rightAnchor).isActive = true        imageView.contentMode = .scaleAspectFit        photoImageView = imageView    }    required init?(coder aDecoder: NSCoder) { super.init(coder: aDecoder) }    override func prepareForReuse() {        super.prepareForReuse()        photoImageView?.image = nil    }}

Result