Run a background thread on Swift 3

Question

I have a function that goes like this:

fileprivate func setupImageViewWithURL(url: URL) {
    var image: UIImage? = nil
    do {
        try image = UIImage(data: Data(contentsOf: url))!
    } catch is NSError {
        print("Failed")
    }

    image = self.imageWithImage(sourceImage: image!, scaledToWidth: UIScreen.main.bounds.size.width)
    self.imageImageView.image = image
    self.imageImageView.frame = CGRect(x: 0, y: 0, width: UIScreen.main.bounds.size.width, height: (image?.size.height)!)
}

I want to run it on a Background thread.

I've tried the GDC methods of Swift2, but it didn't work.

Did anything change in the thread topic in Swift3?

Thank you!

Possible duplicate of [How do I dispatch_sync, dispatch_async, dispatch_after, etc in Swift 3?](http://stackoverflow.com/questions/37801370/how-do-i-dispatch-sync-dispatch-async-dispatch-after-etc-in-swift-3). — Martin R, Oct 06 '16 at 11:33
@FS.O6 I am using it in my code. I don't know the way you are implementing it. Show what error you are getting. — Sachin Vas, Oct 06 '16 at 11:33
You don't want to run it on background thread. UI updates should be never performed on background threads. — Max Pevsner, Oct 06 '16 at 11:43
@MaxPevsner I want to load the image on the background because it's very slow now — FS.O6, Oct 06 '16 at 11:51

score 59 · Accepted Answer · answered Oct 06 '16 at 12:02

It's OK to load image on the background, but it's not OK to perform UI updates on background thread. That's why the function must contain two threads.

func setupImageViewWithURL(url: URL) {
    var image: UIImage? = nil

    DispatchQueue.global().async { 
        do {
            try image = UIImage(data: Data(contentsOf: url))!
        } catch {
            print("Failed")
        }
        DispatchQueue.main.async(execute: {
            if image != nil {
                image = self.imageWithImage(sourceImage: image!, scaledToWidth: UIScreen.main.bounds.size.width)
                self.imageImageView.image = image
                self.imageImageView.frame = CGRect(x: 0, y: 0, width: UIScreen.main.bounds.size.width, height: (image?.size.height)!)
            }
        })
    }
}

`ImageWithImage` is a method that crops the image, can it be done on a background thread? — FS.O6, Oct 06 '16 at 12:04
@FS.O6, I don't think it should be problem. You can test it. — Max Pevsner, Oct 06 '16 at 12:06

score 5 · Answer 2 · answered Apr 12 '18 at 06:12

Swift 4.0

func setupImageViewWithURL(url: URL) {

    var image: UIImage? = nil
    DispatchQueue.global(qos: .background).async {
        do {
            try image = UIImage(data: Data(contentsOf: url))!
        } catch {
            print("Failed")
        }
        DispatchQueue.main.async {
            if image != nil {
                image = self.imageWithImage(sourceImage: image!, scaledToWidth: UIScreen.main.bounds.size.width)
                self.imageImageView.image = image
                self.imageImageView.frame = CGRect(x: 0, y: 0, width: UIScreen.main.bounds.size.width, height: (image?.size.height)!)
            }
        }
    }
}

What is this answer add to the already accepted answer? To me it's just a copy-paste with minimal change. — HMD, Apr 12 '18 at 06:32

score 0 · Answer 3 · answered Jan 05 '18 at 19:28

0

DispatchQueue.global(qos: .background).async {

}

answered Jan 05 '18 at 19:28

Aditya Sharma

585
5
18

Run a background thread on Swift 3

3 Answers3

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