ios - Swift semaphore not waiting for function to finish before calling UI -


i'm trying delay segue until response reversegeocodelocation call. however, when using breakpoints check when value changes, it's still happening after ui transition occurs. i've tried having function void , current string return.

edited code: 

func getreversedgeocodelocation(completionhandler: (string, nserror?) ->()) {      let semaphore = dispatch_semaphore_create(0)      dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_default, 0)) { () -> void in          clgeocoder().reversegeocodelocation(self.newmeetuplocation, completionhandler: {(placemarks, error) -> void in              if error != nil {                 print("reverse geocoder failed error" + error!.localizeddescription)                 return             }             else if placemarks?.count > 0 {              }             else {                 print("problem data received geocoder")             }              completionhandler(placemarks!.first!.name! ?? "", error)         })          dispatch_semaphore_signal(semaphore)      }     dispatch_semaphore_wait(semaphore, dispatch_time_forever) }

old code: 

let semaphore = dispatch_semaphore_create(1) //even 0, it's not working          dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_default, 0)) { () -> void in              self.newaddress = self.getreversedgeocodelocation()              dispatch_semaphore_signal(semaphore)         }          dispatch_semaphore_wait(semaphore, dispatch_time_forever)          //dispatch_semaphore_signal(semaphore)          print(self.newaddress + ".")          self.performseguewithidentifier("maintonewaddress", sender: self)  func getreversedgeocodelocation() -> string{      var address = ""     clgeocoder().reversegeocodelocation(self.newaddresslocation, completionhandler: {(placemarks, error) -> void in          if error != nil {             print("reverse geocoder failed error" + error!.localizeddescription)             return         }         else if placemarks?.count > 0 {             let pm = placemarks?.first!             address = pm!.name!         }         else {             print("problem data received geocoder")         }     })      return address }

using semaphore , dispatching call getreversedgeocodelocation unnecessarily complicated. clgeocoder().reversegeocodelocation asynchronous. if pass completion handler closure getreversedgeocodelocation can use invoke segue;

self.getreversedgeocodelocation(self.newaddresslocation, completionhandler: { (address,error) in      guard error == nil else {         print("reverse geocoder failed error" + error!.localizeddescription)         return     }      guard let address = address else {         print("no address returned")         return     }      self.newaddress = address     dispatch_async(dispatch_get_main_queue(), {         self.performseguewithidentifier("maintonewaddress", sender: self)     }) })  func getreversedgeocodelocation(addresslocation: string, completionhandler:((address: string?, error: nserror?) -> void))) {     clgeocoder().reversegeocodelocation(self.newaddresslocation, completionhandler: {(placemarks, error) -> void in          var address = nil          if placemarks.count > 0 {             if let pm = placemarks!.first {                 address  = pm.name             }         } else {             print("problem data received geocoder")         }          completionhandler(address,error)     }) }

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