ios - Activity Indicator with loop -

i'm working app has loop lot of work. loop generates bunch of numbers, , puts them in uitableview. want display uiactivityindicatorview when work going on. added activity indicator screen , centered it. @ first, wasn't getting activity indicator display @ all. realized because activity indicator running on same thread loop, , indicator never update while loop running. did research on how create background thread, , came this.

    self.progressindicator.startanimating()      dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_background, 0), { () -> void in         var instance = 0; instance < numbercount!; instance++ {             //lots of work done in here.  items added             //collection used populate table view.             //takes around 10 seconds execute.         }         nsnotificationcenter.defaultcenter().postnotificationname("finishednumbers", object: nil)     }); 

the activity indicator running on main thread, , processing of loop running in background. created notifier calls out function call reloadlist , stop activity indicator once list of numbers has completed.

func donewithcreatenumbers(notification: nsnotification) {     self.numberlist.reloaddata()     self.progressindicator.stopanimating() } 

while work, doesn't work well. there couple of problems.

even though processing of loop done in under 10 seconds, takes longer list populate , activity indicator stop spinning. put breakpoint in donewithcreatenumbers function , checked count of numbers collection , have correct number of items in it. after code reload list , stop activity indicator executes, takes between 30 , 40 seconds list populate , activity indicator stop running.

the list populate , indicator goes away, error message in debug window:

this application modifying autolayout engine background thread, can lead engine corruption , weird crashes. cause exception in future release.

i've tried rearranging of in number of ways, nothing has worked better have now. 1 of ways rearranged put reloaddata , stopanimating right after loop. didn't work better, , still got error listed above.

i'm missing here, not sure what. ideas?

try out:

let activityindicator = uiactivityindicatorview.init(activityindicatorstyle:uiactivityindicatorviewstyle.whitelarge) self.view.addsubview(activityindicator)  // switch background thread dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_background, 0)) { () -> void in      // animate activity indicator on main thread     dispatch_async(dispatch_get_main_queue(), { () -> void in         activityindicator.startanimating()     })       // table calculation work here       // stop animating activity indicator on main thread     dispatch_async(dispatch_get_main_queue(), { () -> void in         activityindicator.stopanimating()     }) }