在Swift 3上运行后台线程

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!

Answer 1

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)!)
            }
        })
    }
}

Answer 2

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)!) } } } } 

Answer 3

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

}