ios - Swift Callback change UIViewController Label -

i started study swift ios yesterday , i'm trying make simple login app. swift file

import foundation import swifthttp  func printsomething (sentence: string) {    println(sentence); }  func makelogincall(user: string, pwd: string, donefunction : (bool) -> void) {      var url : string = "myurl"      var request = httptask()      request.requestserializer = jsonrequestserializer()     request.responseserializer = jsonresponseserializer()      request.post(url,          parameters : ["username": user, "password": pwd],          success: {(response: httpresponse) in               if let dict = response.responseobject as? dictionary<string, anyobject> {             println("\(dict)")             donefunction(true)         }         }, failure: {(error: nserror, response: httpresponse?) in             println("error \(error)")             donefunction(false)      })   } 

and viewcontroller

import uikit  class viewcontroller: uiviewcontroller {  @iboutlet weak var usertextfield: uitextfield!  @iboutlet weak var passtextfield: uitextfield!  @iboutlet var resultlabel: uilabel!   override func viewdidload() {     super.viewdidload() }  override func didreceivememorywarning() {     super.didreceivememorywarning()     // dispose of resources can recreated. }   @ibaction func loginbuttoncallback(sender: anyobject) {     checklogin() }  func checklogin() {     var user : string = usertextfield.text     var pass : string = passtextfield.text      makelogincall(user, pass, printresult) }  func printresult(result: bool) -> void {     println("print result function started")     if (result) {         resultlabel.text = "login done"     } else {         resultlabel.text = "login wrong"     } } } 

now printresult function called label won't change. what's problem?

your printresult function runs asynchronously.

all ui changes must dispatched main queue

to main queue use:

dispatch_async(dispatch_get_main_queue(), ^{     donefunction(…) }); 

inside completion block of post request