Changing UILabel text has delay, but why?

Question

in my app I want to set the text of an UILabel. The text comes from a JSON-object. I add my UILabel to my storyboard, set the IBOutlet and

Answer 1

c_rath's answer is correct. In swift 3 the syntax was changed (yet again) to

DispatchQueue.main.async {
    self. label_news?.text = resp.NewsText
}

Answer 2

Like what Rob stated in the comment, all UI changes need to be done on the main thread. I haven't implemented it in Swift yet, but the Objective-C and what I'm assuming would be the Swift is below...

Objective-C

dispatch_async(dispatch_get_main_queue(), ^{
    self.label_news.text = resp.NewsText;
});

Swift:

dispatch_async(dispatch_get_main_queue()) {
    self.label_news.text = resp.NewsText;
}