Converting Array of URLs into Array of UIImage - swift

Question

I have an array of URLs linking to image files, how do I store them into an array of UIImages?
var imagesArray = [UIImage]()
let links = ["http://example.com/image1.jpg","http://example.com/image2.jpg"] as [String]
There must be an easy solution.
If it was one image I could do something like the following:
let url = URL(string: link2image!)!
let imageData = try? Data(contentsOf: url)
let image = UIImage(data: imageData!)!
self.image.append(image)

Answer 1

The easiest solution would be to just iterate through the array and download the images synchronously using Data(contentsOf:), however, this would be quite insufficient due to synchronous execution.
let images = links.flatMap{ link->UIImage? in
guard let url = URL(string: link) else {return nil}
guard let imageData = try? Data(contentsOf: url) else {return nil}
return UIImage(data: imageData)
}
A better solution would be to download the images asynchronously in parallel, I have written a UIImage extension for this using PromiseKit:
extension UIImage {
class func downloadedAsync(fromUrl url: URL)->Promise<UIImage> {
return Promise{ fulfill, reject in
URLSession.shared.dataTask(with: url, completionHandler: { data, response, error in
guard let data = data, error == nil else {
reject(error!); return
}
guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
reject(NSError(domain: "Wrong HTTP response code when downloading image asynchronously",code: (response as? HTTPURLResponse)?.statusCode ?? 1000));return
}
guard let mimeType = response?.mimeType, mimeType.hasPrefix("image"), let image = UIImage(data: data) else {
reject(NSError(domain: "No image in response", code: 700)); return
}
fulfill(image)
}).resume()
}
}
}
You call it for an array of links like this:
var imageDownloadTasks = links.flatMap{ link in
guard let url = URL(string: link) else {return nil}
return UIImage.downloadedAsync(fromUrl: url)
}
Then execute the promises:
when(fulfilled: imageDownloadTasks).then{ images in
//use the images, images is of type [UIImage]
}

Answer 2

Maybe you can try Functional programming use: map closure ...
links.map({
if let imageData = try? Data(contentsOf: URL(string: $0)!) {
UIImage(data: imageData)
}
})
But you must know if your links is wrong, it will crash. So, I suggest you make some guard to prevent these crashes. like this...
guard let url = URL(string: $0) else { return nil }