ios - Using @IBInspectable setting a Bool failed -

this class:

class viewcontroller: uiviewcontroller {      @ibinspectable var double: double!     @ibinspectable var string: string!       override func viewdidload() {         super.viewdidload()     }      override func didreceivememorywarning() {         super.didreceivememorywarning()     }  } 

and set double , string in storyboard

i run app. string can set correctly double failed.the console output:

failed set (double) user defined inspected property on (test1.viewcontroller): [<test1.viewcontroller 0x7f892ad25910> setvalue:forundefinedkey:]: class not key value coding-compliant key double. 

could tell me why setting failed ? thanks!