ios - Push doesn't work after back button? -

i'm working on app scans barcode , segues new view controller after scan found. however, if user clicks button (navigation controller, root view controller main menu, [probably] irrelevant), view controller not segue again. segues forward view controller 3 first time app runs, upon hitting "back" , returning vc 2, won't segue vc 3 again. there i'm missing? set handler in viewdidload:

        self.barcodeshandler = { barcodes in             if(self.handler_flag) {                 var barcode = barcodes[0]                 println("barcode found: type=" + barcode.type + " value=" + barcode.stringvalue)                 self.bcode = barcode.stringvalue                 self.handler_flag=false                 self.performseguewithidentifier("push", sender: nil)             }         } 

and segue:

override public func prepareforsegue(segue: uistoryboardsegue, sender: anyobject?) {     let destinationvc = segue.destinationviewcontroller as! secondviewcontroller     destinationvc.settext = bcode    } 

thanks much!

self.performseguewithidentifier("push", sender: nil) 

instead of nil use self