why downloading image from url returns nil?

Question

I am trying to download an image that is uploaded to my database storage and the link to the image is in my Real time database. There is no problem with the link but when I use my method to return the image from the link I am getting nil. I force wrap it because it needs to return an image for now.

This is my code:

func getImageFromUrl(url: URL) -> UIImage {
    var tempImage: UIImage? = nil

    print("INSIDE URL -> \(url.absoluteString)")

    URLSession.shared.dataTask(with: url) { (data, response, error) in
       if error != nil {
           print("Error on getImageFromUrl : \(error!.localizedDescription)")
           return
       }

       print("Image data " + data.debugDescription)

       DispatchQueue.main.async {
           tempImage = UIImage(data: data!)!
           print("TEMP IMAGE > \(String(describing: tempImage?.images![0]))")
       }
    }.resume()

    if tempImage == nil {
        print("IMAGE IS NIL!")
    }
    return tempImage!
 }

Please let me know why my code is failing.

the download method is asynchronous. You are returning the result before the download process is completed. What you need is to add a completion handler to your method — Leo Dabus, Aug 27 '18 at 02:47

Leo Dabus · Accepted Answer · 2018-08-27T03:12:08.863

1

The problem with your code is that the dataTask method is asynchronous. You are returning the result before the download process is completed. What you need is to add a completion handler to your method to return the image or the error once finished:

import UIKit
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

func getImage(from url: URL, completion: @escaping (UIImage?, Error?) -> ()) {
    print("download started:", url.absoluteString)
    URLSession.shared.dataTask(with: url) { data, reponse, error in
        guard let data = data else {
            completion(nil, error)
            return
        }
        print("download finished:")
        completion(UIImage(data: data), nil)
    }.resume()
}

let url = URL(string: "https://i.stack.imgur.com/varL9.jpg")!
getImage(from: url) { image, error in
    guard let image = image else {
        print("error:", error ?? "")
        return
    }
    print("image size:", image.size)
    // use your image here and don't forget to always update the UI from the main thread
    DispatchQueue.main.async {
        self.imageView.image = image
    }
}

edited Aug 27 '18 at 03:12

answered Aug 27 '18 at 02:56

Leo Dabus

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I used the following code but I am getting this error: The requested URL was not found on this server. I can se see the URL is on my Firebase database. What could this be? – GreekShadow Aug 27 '18 at 13:04
Show your url. Have you tested it in your desktop browser? What happens? – Leo Dabus Aug 27 '18 at 13:09
If I copy and paste my url in the browser it automatically downloads a jpg. This is the url -> https://firebasestorage.googleapis.com/v0/b/the-spot-6bdd6.appspot.com/o/user%2FnC2ayJaTVSOe5qUXWOCJ1ILbIuT2%2F1%2F0.jpg?alt=media&token=789d3875-789f-4691-806f-404782b19252 – GreekShadow Aug 27 '18 at 14:05
Just pasted your link in my playground and it printed `"image size: (3072.0, 2304.0)\n"` – Leo Dabus Aug 27 '18 at 14:07
Try using the UIImageView extension I posted here https://stackoverflow.com/a/27712427/2303865 – Leo Dabus Aug 27 '18 at 14:10
Hum ok thank you I will try it. – GreekShadow Aug 27 '18 at 14:12
I am getting this error { "error": { "code": 403, "message": "Permission denied. Could not perform this operation" } } – GreekShadow Aug 27 '18 at 15:02
Check if you are using the proper token – Leo Dabus Aug 27 '18 at 15:08
Your link is expired. try clicking the link you posted above `{ "error": { "code": 403, "message": "Permission denied. Could not perform this operation" } }` – Leo Dabus Aug 27 '18 at 15:09
It is returning a json string instead of an image – Leo Dabus Aug 27 '18 at 15:10
How is it expiring if I am uploading and downloading after I upload. – GreekShadow Aug 28 '18 at 00:53

why downloading image from url returns nil?

1 Answers1