ios - UIAlertController in swift -

i creating view controller in swift few text fields , accept button confirms user's input. accept button checks if of text fields empty. if so, pop alert saying it cannot empty. if not empty, store input , jump view.

i created separated function called checempty() looks this:

    func checempty(title: string, object: uitextfield) -> (bool) {         if object.text.isempty {             let alertcontroller = uialertcontroller(title: "invalid input",                  message:"\(title) cannot empty",                  preferredstyle: uialertcontrollerstyle.alert)              alertcontroller.addaction(uialertaction(title: "dismiss",                  style: uialertactionstyle.default)              self.presentviewcontroller(alertcontroller, animated: true, completion: nil)              return false         } else {             return true         }     } 

and call function in acceptbutton action:

   @ibaction func acceptbutton(sender: uibutton){          if(checempty("event", object: eventname) && checempty("priority", object: priority)          {                  //if not empty, confirm user input                // ...          } 

when run it, alert message works fine reason console shows this:

2015-08-03 12:11:50.656 finishittoday[13777:688070] >'s window not equal 's view's window!

can tell me why warning appears? thank much!

ps. want if of text field empty, show alert , stay @ same page. if none of them empty, perform segue , switch view. code above works fine except warning.

here working code:

import uikit  class viewcontroller: uiviewcontroller {      @iboutlet weak var eventname: uitextfield!     @iboutlet weak var priority: uitextfield!      @ibaction func acceptbutton(sender: uibutton){          if checempty("event", object: eventname) && checempty("priority", object: priority){             println("both text fields empty")         }     }      func checempty(title: string, object: uitextfield) -> (bool) {         if object.text.isempty {              var alert = uialertcontroller(title: "invalid input", message: "\(title) cannot empty", preferredstyle: uialertcontrollerstyle.alert)              alert.addaction(uialertaction(title: "dismiss", style: .cancel, handler: { action in                 println("click of cancel button")             }))             self.presentviewcontroller(alert, animated: true, completion: nil)              return false         } else {             return true         }     } }