Using threads to update UI with Swift - xcode

Question

I'm developing a software with Xcode 6 using Swift. When I press a button, my code takes some informations from the web and writes them on my NSWindow.
So imagine something like this:
#IBAction func buttonPressed(sender: AnyObject)
{
for page in listOfPages //Number of pages is 40.
{
var label: NSTextField = NSTextField();
label.stringValue = getInformetionsFromPage(page)
/*
some code to add label in the window here
*/
}
}
The problem is that once I click the button, it takes a while before I see the list of results, in the main time the app is frozen. That's because I'm not using any threads to handle this problem. How could I implement threads to see every label updated every step of the loop? I'm new with threads and Swift, so I would need some help!
Thank you guys.

Answer 1

Swift 3.0 + version
DispatchQueue.main.async() {
// your UI update code
}
Posted this because XCode cannot suggest the correct syntax from swift 2.0 version

Answer 2

There is GCD. Here is a basic usage:
for page in listOfPages {
var label = NSTextField()
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
let result = getInformationFromPage(page)
dispatch_async(dispatch_get_main_queue()) {
label.stringValue = result
}
}
}
dispatch_async function asynchronously runs the block of code on the given queue. In first dispatch_async call we dispatch the code to run on background queue. After we get result we update label on main queue with that result