ios - First time launch / segue swift -

what trying accomplish once app launched check first time use. if first time use take view controller enter credentials, else take to main menu of app. have far every time launch give me blank page error message of "a segue must either have performhandler or must override -perform. " have both segues linked on storyboard. can 1 please steer me in right direction.

    let defaults = userdefaults.standard     if defaults.string(forkey: "isappalreadylaunchedonce") != nil{         print("first time")         self.performsegue(withidentifier: "totoken", sender: nil)     }else{         defaults.set(true, forkey: "isappalreadylaunchedone")         defaults.synchronize()         print("not first")         self.performsegue(withidentifier: "tomainmenu", sender: nil)     } 

your method confusing. way go problem shown below.

override viewdidload() { super.viewdidload  let checkforfirsttimelaunch = userdefaults.standard.string(forkey: "flag")  if checkforfirsttimelaunch == nil { print("first time launch")  //if user launches app first time, go here  } else { //otherwise, go here  }  }