Using threads to update UI with Swift

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