Swift 3 warning for dispatch async

Question

I have this code:

DispatchQueue.global(priority: DispatchQueue.GlobalQueuePriority.default).async {
                let url = URL(string: itemImageURL )
                let data = try? Data(contentsOf: url!)
                if data != nil {
                    DispatchQueue.main.async{
                        cell.advImage!.image = UIImage(data: data!)
                    }
                }
            }

I get this warning in Swift 3:

'default' was deprecated in iOS 8.0: Use qos attributes instead

on the first line.

Haven't found yet a solution. Has anybody?

Answer 1

try qos: DispatchQoS.QoSClass.default instead of priority: DispatchQueue.GlobalQueuePriority.default

DispatchQueue.global(qos: DispatchQoS.QoSClass.default).async {
            let url = URL(string: itemImageURL )
            let data = try? Data(contentsOf: url!)
            if data != nil {
                DispatchQueue.main.async{
                    cell.advImage!.image = UIImage(data: data!)
                }
            }
        }

Answer 2

Instead of using priority parameter:

DispatchQueue.global(priority: DispatchQueue.GlobalQueuePriority.default).async {
 // ...
}

use qos parameter that uses a different enum DispatchQoS.QoSClass.default but you can also use its enum value as just .default:

DispatchQueue.global(qos: .default).async {
 // ...
}

Swift 3 has brought many changes on GCD(Grand Central Dispatch).

Answer 3

If you're creating a property using the Dispatch Framework and updating the UI with some animation within a function it might look something like this.

let queue = DispatchQueue.global(qos: DispatchQoS.QoSClass.default)
    // dispatch_after says that it will send this animation every nsec
    queue.asyncAfter(deadline: when) {
        DispatchQueue.main.async(execute: {
            self.animate(withDuration: 0.5, animations: {
                self.image.setWidth(35)
                self.image.setHeight(35)
            })
        })
    }

Answer 4

Below code is tested for Swift 3.0 on Xcode 8.2.1

DispatchQueue.global(qos: .background).async {
            let img2 = Downloader.downloadImageWithURL(imageURLs[1])

            // Background Thread
            DispatchQueue.main.async {

                // Run UI Updates
                self.imageView2.image = img2
            }
        }

where property of QoS are :

background, utility, `default`, userInitiated, userInteractive and unspecified

Refer this apple document for more details.