ios - Calling upon the previous view controller in Swift -

i trying call upon root controller , don't know code call upon it. i'm using conditional , check previous view controller was, , block of code run depending on was. here code:

secondviewcontroller

override func viewdidload ( ) {      super.viewdidload ( )       let previouscontroller = storyboard!.instantiateviewcontrollerwithidentifier ("firstviewcontroller") as? firstviewcontroller       //help in line below      //if root view controller == previouscontroller {               //run code      //} } 

let stack = self.navigationcontroller.viewcontrollers if (stack.count > 1) {     let previouscontroller = stack[stack.count-2] } 

or if don't have navigation controller

let previouscontroller = self.presentingviewcontroller 

also, clear, root view controller first view controller in stack, i.e:

self.navigationcontroller.viewcontrollers.firstobject 

or

var previouscontroller : uiviewcontroller = self var rootcontroller : uiviewcontroller? {     var rootviewcontroller = previouscontroller     var previouscontroller = rootviewcontroller.presentingviewcontroller } while (previouscontroller != nil)