ios - Swift NSUserDefaults app crash first time -

my app crash every time installed it, first time..

this code

 var state = save.stringforkey("statesave")     var city = save.stringforkey("citysave")     var vehicle = save.stringforkey("modelnumbersave")     var extensionperiod = save.stringforkey("extensionperiodchoosed")     var location = "location"       if extensionperiod == nil {         var name = ""         var fieldchoosed: void = save.setobject(name, forkey: "extensionperiodchoosed")         save.synchronize()      }      save.synchronize()     var detailnames = ["\(state!)","\(city!)","\(location)","\(vehicle!)","\(extensionperiod!)"] 

it crash because extensionperiod nil. think it's because of nsuserdefaults in if statement. first idea put save.synchronize var save = nsuserdefaults.standarduserdefaults() didn't work :\

your app crashes because in line:

var detailnames = ["\(state!)","\(city!)","\(location)","\(vehicle!)","\(extensionperiod!)"] 

you using force unwrap operator. need make sure these values aren't nil before unwrapping them.

from the swift programming language: basics:

trying use ! access non-existent optional value triggers runtime error. make sure optional contains non-nil value before using ! force-unwrap value.

you can provide default values using nil coalescing operator:

var state = save.stringforkey("statesave") ?? "texas" var city = save.stringforkey("citysave") ?? "el paso" 

as stylistic note, instance variables should begin lowercase letters. type names should begin uppercase letters.