ios - Activity Indicator not appearing -

i have heavy code runs around 0.2 seconds.

i set activity indicator this; however, doesn't show up, rather whole screen freezes around 0.2seconds until code finishes.

func heavywork() {     self.actvityindicator.startanimating()      ...     // heavy loop codes here     ...      self.activityindicator.stopanimating() } 

is correct way of using activity indicator?

when comment out

// self.activityindicator.stopanimating() 

the activity indicator shows , stays there - codes set right.

but ui doesn't seem updated @ right time.

as said, screen freezes without showing activity indicator until heavy code done.

maybe want carry on such pattern instead:

func heavywork() {     self.actvityindicator.startanimating()      dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_default, 0), { () -> void in          // ...         // heavy loop codes here         // ...          dispatch_async(dispatch_get_main_queue(), { () -> void in             self.activityindicator.stopanimating()         })     }); } 

as heavy work should happen in background thread , need update ui on main thread after.

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note: assumed call the func heavywork() on main thread; if not, might need distract initial ui updates main thread well.