ios - childViewControllers is empty after calling addChildViewController -


i have question regarding add/remove childviewcontrollers containerview.

i have uiviewcontroller named "containerviewcontroller" contains containerview, , containerview has uiviewcontroller named "containerlinkviewcontroller". have 4 other uiviewcontrollers added or removed "containerlinkviewcontroller" whenever user clicks 1 of tab button placed @ bottom of "containerviewcontroller". storyboard looks below.

enter image description here

note custom segues connected 4 uiviewcontrollers empty segue nothing show visual connection in storyboard.

so first add first tab viewcontroller "containerlinkviewcontroller" childviewcontroller using below code in viewdidload().

let firsttabviewcontroller = self.storyboard?.instantiateviewcontroller(withidentifier: "firsttabviewcontroller") as! firsttabviewcontroller self.addchildviewcontroller(firsttabviewcontroller) firsttabviewcontroller.view.frame = self.view.bounds self.view.addsubview(firsttabviewcontroller.view) firsttabviewcontroller.didmove(toparentviewcontroller: self)

after initial setup, whenever user tabs on 1 of tab buttons, send signal "containerviewcontroller" uiviewcontroller added new childviewcontroller "containerlinkviewcontroller" , switching old childviewcontroller , new childviewcontroller using below code.

func swapviewcontrollers(from : uiviewcontroller, : uiviewcontroller) {     from.willmove(toparentviewcontroller: nil)     self.addchildviewcontroller(to)     to.view.frame = self.view.bounds      self.transition(from: from, to: to, duration: 1.0, options: uiviewanimationoptions.transitioncrossdissolve, animations: nil) {         finished in         from.view.removefromsuperview()         from.removefromparentviewcontroller()         to.didmove(toparentviewcontroller: self)     } }

before calling "swaptviewcontrollers()", take old childviewcontroller doing following.

let oldchildviewcontroller = self.childviewcontrollers.last

my problem "oldchildviewcontroller" nil when click 1 of tabs first time right after initial setup. function "swaptviewcontrollers()" not called because self.childviewcontrollers empty.

i have been struggling few days , not find clear answer solve this. decided ask here might cause this.

any help?? thanks.

note : using swift 3. maybe answer question since seems lots of things changed fro swift 2.


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