Loading/Downloading image from URL on Swift

Question

I'd like to load an image from a URL in my application, so I first tried with Objective-C and it worked, however, with Swift, I've a compilation error:

'imageWithData' is unavailable: use object construction 'UIImage(data:)'

My function:

@IBOutlet var imageView : UIImageView

override func viewDidLoad() {
    super.viewDidLoad()

    var url:NSURL = NSURL.URLWithString("http://myURL/ios8.png")
    var data:NSData = NSData.dataWithContentsOfURL(url, options: nil, error: nil)

    imageView.image = UIImage.imageWithData(data)// Error here
}

In Objective-C:

- (void)viewDidLoad {
    [super viewDidLoad];

    NSURL *url = [NSURL URLWithString:(@"http://myURL/ios8.png")];
    NSData *data = [NSData dataWithContentsOfURL:url];

    _imageView.image = [UIImage imageWithData: data];
    _labelURL.text = @"http://www.quentinroussat.fr/assets/img/iOS%20icon's%20Style/ios8.png";
 }

Can someone please explain me why the imageWithData: doesn't work with Swift, and how can I solve the problem.

Answer 1

Kingfisher is one of the best library for load image into URL.

Github URL - https://github.com/onevcat/Kingfisher

// If you want to use Activity Indicator.
imageview_pic.kf.indicatorType = .activity
imageview_pic.kf.setImage(with: URL(string: "Give your url string"))

// If you want to use custom placeholder image.
imageview_pic.kf.setImage(with: URL(string: "Give your url string"), placeholder: UIImage(named: "placeholder image name"), options: nil, progressBlock: nil, completionHandler: nil)

Answer 2

The only things there is missing is a !

let url = NSURL.URLWithString("http://live-wallpaper.net/iphone/img/app/i/p/iphone-4s-wallpapers-mobile-backgrounds-dark_2466f886de3472ef1fa968033f1da3e1_raw_1087fae1932cec8837695934b7eb1250_raw.jpg");
var err: NSError?
var imageData :NSData = NSData.dataWithContentsOfURL(url!,options: NSDataReadingOptions.DataReadingMappedIfSafe, error: &err)
var bgImage = UIImage(data:imageData!)

Answer 3

Xcode 8 • Swift 3

Leo Dabus's answer is awesome! I just wanted to provide an all-in-one function solution:

let url = URL(string: 
    "http://www.apple.com/euro/ios/ios8/a/generic/images/og.png")

let task = URLSession.shared.dataTask(with: url!) { data, response, error in
    guard let data = data, error == nil else { return }

    DispatchQueue.main.async() {    // execute on main thread
        self.imageView.image = UIImage(data: data)
    }
}

task.resume()

Answer 4

(Swift 4 update) To answer the original question directly, here's the swift equivalent of the posted Objective-C snippet.

let url = URL(string: image.url)
let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
imageView.image = UIImage(data: data!)

---

DISCLAIMER:

It's important to note that the Data(contentsOf:) method will download the contents of the url synchronously in the same thread the code is being executed, so do not invoke this in the main thread of your application.

An easy way to make the same code run asynchronously, not blocking the UI, is by using GCD:

let url = URL(string: image.url)

DispatchQueue.global().async {
    let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
    DispatchQueue.main.async {
        imageView.image = UIImage(data: data!)
    }
}

That said, in real life applications, if you want to have the best User Experience and avoid multiple downloads of the same image, you may want to also have them not only downloaded, but cached. There's already quite a few libraries that does that very seamless and they are all really easy to use. I personally recommend Kingfisher:

import Kingfisher

let url = URL(string: "url_of_your_image")
// this downloads the image asynchronously if it's not cached yet
imageView.kf.setImage(with: url) 

And that's it

Answer 5

I recommend using Kingfisher library to download images asynchronously. The best part about using Kingfisher is, it caches all the downloaded images by default with the image url as an id. Next time when you request to download image with that particular URl, it will load it from cache.

Usage:

newsImage.kf.setImage(with: imageUrl!, placeholder: nil, options: nil, progressBlock: nil, completionHandler: { (image, error, cacheType, imageUrl) in
                if error == nil{
                    self.activityIndicator.stopAnimating()
                }else if error != nil{
                    self.activityIndicator.stopAnimating()
                }
            })

Answer 6

class func downloadImageFromUrl(with urlStr: String, andCompletionHandler:@escaping (_ result:Bool) -> Void) {
        guard let url = URL(string: urlStr) else {
            andCompletionHandler(false)
            return
        }
        DispatchQueue.global(qos: .background).async {
            URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) -> Void in
                if error == nil {
                    let httpURLResponse = response as? HTTPURLResponse
                    Utils.print( "status code ID : \(String(describing: httpURLResponse?.statusCode))")
                    if httpURLResponse?.statusCode == 200 {
                        if let data = data {
                            if let image = UIImage(data: data) {
                                ImageCaching.sharedInterface().setImage(image, withID: url.absoluteString as NSString)
                                DispatchQueue.main.async {
                                    andCompletionHandler(true)
                                }
                            }else {
                                andCompletionHandler(false)
                            }
                        }else {
                            andCompletionHandler(false)
                        }
                    }else {
                        andCompletionHandler(false)
                    }
                }else {
                    andCompletionHandler(false)
                }
            }).resume()
        }
    }

I have created a simple class function in my Utils.swift class for calling that method you can simply accesss by classname.methodname and your images are saved in NSCache using ImageCaching.swift class

Utils.downloadImageFromUrl(with: URL, andCompletionHandler: { (isDownloaded) in
                            if isDownloaded {
                                if  let image = ImageCaching.sharedInterface().getImage(URL as NSString) {
                                    self.btnTeam.setBackgroundImage(image, for: .normal)
                                }
                            }else {
                                DispatchQueue.main.async {
                                    self.btnTeam.setBackgroundImage(#imageLiteral(resourceName: "com"), for: .normal)
                                }
                            }
                        })

Happy Codding. Cheers:)