Change a variable within a URLSession callback - swift

Question

I want to check if a file exists and then change the context of a variable.
If I'm working with playgrounds, it will work but coding in a viewport, nothing happens.
I check if the file named "nameoffile.xml" exist, using the statuscode, and then the var color need to change into "blue".
Below you will find my (not working) code.
let url = URL(string: "http://myurl/nameoffile.xml")!
var color = ""
func checkFile()
{
let req = NSMutableURLRequest(url: url)
req.httpMethod = "HEAD"
req.timeoutInterval = 1.0
var response: URLResponse?
var task = URLSession.shared.dataTask(with: url) {(data, response, error) in
if let httpStatus = response as? HTTPURLResponse
{ if httpStatus.statusCode == 200 {
self.kleur = "blue"
}
}
}

Answer 1

From your example it isn't totally clear if the color and url are attributes of the class you are calling checkFile on. I'll assume they are, because it makes the most sense.
So if the colour you want to change is an attribute of UIView.backgroundColor and you want to see the change immediately, you need to change it on a main thread like this:
// Your view controller you are using for the task
class MyViewController: UIViewController {
// The ui element you want to change the colour of
// If you are using a storyboard you would have a #IBOutlet here
let button = UIButton()
func checkFile() {
// I've noticed you aren't using the NSMutableURLRequest anywhere
// Also I've cleaned up your code a bit, hope you don't mind
URLSession.shared.dataTask(with: url) { data, response, error in
guard let httpStatus = response as? HTTPURLResponse else {
return
}
if httpStatus.statusCode == 200 {
DispatchQueue.main.async {
// This line of code will change the color
self.button.backgroundColor = .blue
}
}
}
}
}
Hope this helps. If I haven't guessed your problem, feel free to change your question or leave a comment.