iOS迅速而循环循环冻结我的应用程序

Question

I'm developing an app where a user choose his accommodation and pick a time from date picker so the user can know what time the buss will arrive to his accommodation , on the simulator and iPad I'm having the appropriate results however I'm facing this issue on iPhone real device, this is the code :

mTimeString = "5:07 AM"

it will be searched in the array if not found , minus seconds until it matches results in the array . but while loop is freezing my app , i tried to surround it by :

let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT ,0)
dispatch_async(queue){}

its not freezing anymore but the I'm not getting the results according to the array

if(defaults.stringForKey(accommodationChoiceKey)?.toInt() == 40) {

    var  array = ["12:05 AM","12:25 AM","12:45 AM","1:05 AM","1:25 AM","1:45 AM","2:05 AM","2:25 AM","2:45 AM","3:05 AM","3:25 AM","3:45 AM","4:05 AM","4:25 AM","4:45 AM","5:05 AM","5:25 AM","5:45 AM","6:05 AM","6:25 AM","6:45 AM","7:05 AM","7:25 AM","7:45 AM","8:05 AM","8:25 AM","8:45 AM","9:05 AM","9:25 AM","9:45 AM","10:05 AM","10:25 AM","10:45 AM","11:05 AM","11:25 AM","11:45 AM","12:05 PM","12:25 PM","12:45 PM","1:05 PM","1:25 PM","1:45 PM","2:05 PM","2:25 PM","2:45 PM","3:05 PM","3:25 PM","3:45 PM","4:05 PM","4:25 PM","4:45 PM","5:05 PM","5:25 PM","5:45 PM","6:05 PM","6:25 PM","6:45 PM","7:05 PM","7:25 PM","7:45 PM","8:05 PM","8:25 PM","8:45 PM","9:05 PM","9:25 PM","9:45 PM","10:05 PM","10:25 PM","10:45 PM","11:05 PM","11:25 PM","11:45 PM"]
    while (find(array, mTimeString) == nil) {
        choiceToSeconds--
        var newmTime = x.dateByAddingTimeInterval(Double(choiceToSeconds))
        var mTimeString = dateFormatter.stringFromDate(newmTime)
        if (find(array, mTimeString) != nil) {
            transportationLabel.text = mTimeString
            break
        }
        getReady(newmTime)
    }
}

Answer 1

You are calculating on Background thread which is okay , but you should NEVER update UI element from background thread ( transportationLabel.text = mTimeString ) , this should be done from main Thread , for example

    let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
    dispatch_async(dispatch_get_global_queue(priority, 0)) {

         if(defaults.stringForKey(accommodationChoiceKey)?.toInt() == 40) {

                var  array = ["12:05 AM","12:25 AM","12:45 AM","1:05 AM","1:25 AM","1:45 AM","2:05 AM","2:25 AM","2:45 AM","3:05 AM","3:25 AM","3:45 AM","4:05 AM","4:25 AM","4:45 AM","5:05 AM","5:25 AM","5:45 AM","6:05 AM","6:25 AM","6:45 AM","7:05 AM","7:25 AM","7:45 AM","8:05 AM","8:25 AM","8:45 AM","9:05 AM","9:25 AM","9:45 AM","10:05 AM","10:25 AM","10:45 AM","11:05 AM","11:25 AM","11:45 AM","12:05 PM","12:25 PM","12:45 PM","1:05 PM","1:25 PM","1:45 PM","2:05 PM","2:25 PM","2:45 PM","3:05 PM","3:25 PM","3:45 PM","4:05 PM","4:25 PM","4:45 PM","5:05 PM","5:25 PM","5:45 PM","6:05 PM","6:25 PM","6:45 PM","7:05 PM","7:25 PM","7:45 PM","8:05 PM","8:25 PM","8:45 PM","9:05 PM","9:25 PM","9:45 PM","10:05 PM","10:25 PM","10:45 PM","11:05 PM","11:25 PM","11:45 PM"]
                while (find(array, mTimeString) == nil) {
                    choiceToSeconds--
                    var newmTime = x.dateByAddingTimeInterval(Double(choiceToSeconds))
                    var mTimeString = dateFormatter.stringFromDate(newmTime)
                    if (find(array, mTimeString) != nil) {

                        //  This should be done on Main Thread
                        dispatch_async(dispatch_get_main_queue()) {
                            transportationLabel.text = mTimeString
                        }      


                        break
                    }
                    getReady(newmTime)
                }
            }
    }

Answer 2

Try replacing

transportationLabel.text = mTimeString

by

[[NSOperationQueue mainQueue] addOperationWithBlock:^{
     transportationLabel.text = mTimeString
}];

UI operations must be executed from main thread

EDIT:

In Swift:

NSOperationQueue.mainQueue().addOperationWithBlock({
    transportationLabel.text = mTimeString
})