ios - Countdown with several decimal slots, using NSTimer in Swift -

i want make app has timer starting @ 10.0000000 example, , want countdown here's code far:

import uikit  class viewcontroller: uiviewcontroller {      @iboutlet weak var labeltime: uilabel!      var counter = 10.0000000      var labelvalue: double {         {             return nsnumberformatter().numberfromstring(labeltime.text!)!.doublevalue         }         set {             labeltime.text = "\(newvalue)"         }     }       override func viewdidload() {         super.viewdidload()         // additional setup after loading view, typically nib.         labelvalue = counter         var timer = nstimer.scheduledtimerwithtimeinterval(0.0000001, target: self, selector: ("update"), userinfo: nil, repeats: true)     }      func update(){         labelvalue -= 0.0000001     }   } 

what happens countdown slow, it's not working , take 1 hour 0 seconds, instead of 10 seconds. ideas? changes should make code? thanks

timers not super-accurate, , resolution of nstimer 1/50th of second.

plus, refresh rate of iphone screen 60 frames/second, it's totally pointless run timer faster that.

rather trying use timer decrement every time fires, create timer fires 50 times second, , have use clock math update display based on remaining time:

var futuretime: nstimeinterval   override func viewdidload() {     super.viewdidload()     labelvalue = counter      //futuretime value 10 seconds in future.     futuretime = nsdate.timeintervalsincereferencedate() + 10.0       var timer = nstimer.scheduledtimerwithtimeinterval(       0.02,        target: self,        selector: ("update:"),        userinfo: nil,        repeats: true) }  func update(timer: nstimer) {   let timeremaining = futuretime - nsdate.timeintervalsincereferencedate()   if timeremaining > 0.0   {     label.text = string(format: "%.07f", timeremaining)   }   else   {     timer.invalidate()     //force label 0.0000000 @ end     label.text = string(format: "%.07f", 0.0)   } }