uitableview - How to use Asychronous task inside for loop in swift -

i using google map in project. calculating place distance current location nd showing tableview. there multiple places , want show in tableview. each place , distance current location need call google distancematrix api. able store places cordinate inside array , looping through array calling distance martix api.

here code

 func calculatedistance(type : string)     {         let currentlocationcordinate = "\(usercurrentlocation.coordinate.latitude),\(usercurrentlocation.coordinate.longitude)"          var url = string()         var remoteurl = nsurl()         var request = nsurlrequest()         var session = nsurlsession()         var locatioarrayindex = 0          //locationarray stores cordinate of nearby array         locatioarrayindex in 0...locationarray.count-1          {             placecordinationarray = "\(locationarray[locatioarrayindex].coordinate.latitude),\(locationarray[locatioarrayindex].coordinate.longitude)"              url = "https://maps.googleapis.com/maps/api/distancematrix/json?units=imperial&origins=\(currentlocationcordinate)&destinations=\(placecordinationarray)&key=\(key)"               remoteurl = nsurl(string: url)!              request = nsurlrequest(url: remoteurl)             let config1 = nsurlsessionconfiguration.defaultsessionconfiguration()             session = nsurlsession(configuration: config1)              // asych start here             let task = session.datataskwithrequest(request, completionhandler: {(data, response, error) in               // convert server json response nsdictionary             {                  let convertedjsonintodict = try nsjsonserialization.jsonobjectwithdata(data!, options: [])                  let rows = convertedjsonintodict["rows"] as! nsarray                  let elements = rows[0]                  let element1 = elements["elements"] as! nsarray                  let distance = element1[0]                  let distancedictionary = distance["distance"]                  let testdistance = distancedictionary!!["text"]  as! string!                 self.distancemeter = testdistance                 self.placedistantarray.append(self.distancemeter)                      if (locatioarrayindex == 9)                     {                     dispatch_async(dispatch_get_main_queue(),                         {                             self.seguecheck = true                             self.searchactivityindicator.stopanimating()                             self.searchactivityindicator.hideswhenstopped = true                             self.tableview.reloaddata()                    })                 }                     //                     print("location array indexinside",locatioarrayindex)                  }                  catch let error nserror                 {                     print("some error ",error.localizeddescription)                 }             })              task.resume()           }// loop closed        } 

i storing distance in self.placedistantarray array. , after reloading tableview data. values in self.placedistantarray reapeting sometimes. , tableview sometime array index error

you code very unclean , not readable @ all, cleaned it:

func calculatedistanceupdatingui(type : string) {     //locationarray stores cordinate of nearby array     (index, location) in locationarray.enumerate()     {         if let remoteurl = distancecalculationurlfrom(usercurrentlocation, todestination: location) {             let request = nsurlrequest(url: remoteurl)             let session = nsurlsession(configuration: nsurlsessionconfiguration.defaultsessionconfiguration())              // clear array             self.placedistantarray.removeall()              // request distance             let task = session.datataskwithrequest(request, completionhandler: {(data, response, error) in                                  {                     if let distancemeter = try self.testdistancefrom(data) {                         self.distancemeter = distancemeter                         self.placedistantarray.append(distancemeter)                     }                      if (index == 9)                     {                         self.updateui()                     }                      print("location array indexinside", index)                 }                 catch let error nserror                 {                     print("some error ", error.localizeddescription)                 }             })              task.resume()         }     } }  private func updateui() {     dispatch_async(dispatch_get_main_queue())     {         self.seguecheck = true         self.searchactivityindicator.stopanimating()         self.searchactivityindicator.hideswhenstopped = true         self.tableview.reloaddata()     } }  private func distancecalculationurlfrom(origin: cllocation, todestination destination: cllocation) -> nsurl? {     var urlstring = "https://maps.googleapis.com/maps/api/distancematrix/json?units=imperial&origins="     urlstring += "\(origin.coordinate.latitude),\(origin.coordinate.longitude)&destinations="     urlstring += "\(destination.coordinate.latitude),\(destination.coordinate.longitude)&key=\(key)"     return nsurl(string: urlstring) }  private func testdistancefrom(data: nsdata?) throws -> string? {     guard let data = data else {         return nil     }     let convertedjsonintodict = try nsjsonserialization.jsonobjectwithdata(data, options: [])     if let rows = convertedjsonintodict["rows"] as? nsarray rows.count > 0,         let element1 = rows[0]["elements"] as? nsarray element1.count > 0,         let distancedictionary = element1[0]["distance"] as? nsdictionary,         let testdistance = distancedictionary["text"] as? string     {         return testdistance     }      return nil } 

here goes advice:

• you should not use forced unwrapping lightly.
• you should try avoid using old style loops, try use fast enumeration (more readable).
• your functions should not have side effects. if call function calculatedistance should that, calculate distance. not change variables such placecordinationarray or update ui.
• you should try split code , make smaller functions. if have add comments // loop closed it's large
• you should not initialise object won't using (as in var request = nsurlrequest())
• try use correct words, such coordinate instead of cordination or location instead of locatio.

as @jigar tarsariya said, cleaned array before filled again.