ios - Swift Firebase check authentication more smoothly -

i'm setting window's root view controller login controller right off bat, , login controller checks user authentication firebase. if user logged in, controller changes root view controller feed controller. otherwise, login controller proceeds itself.

class logincontroller: uiviewcontroller {      override func viewdidload() {         super.viewdidload()          if let uid = auth.auth().currentuser?.uid {              database.database().reference().child("users").observesingleevent(of: .value, with: { snapshot in                 if snapshot.haschild(uid) {                     appdelegate.launchapplication()                 }                 else {                     self.setupui()                 }             })          }         else {             self.setupui()         }      } ... } 

where launchapplication is

class func launchapplication() {     guard let window = uiapplication.shared.keywindow else { return }     window.rootviewcontroller = uinavigationcontroller(rootviewcontroller: feedcontroller()) } 

in addition if let uid = auth.auth().currentuser?.uid, i'm checking whether uid (if isn't nil) exists in database, because have had situation deleted user still wasn't nil.

the problem after launch screen finishes, there moment when login controller, though blank, visible. moment lasts few seconds. how can check authentication such login controller isn't visible @ all—so app decides how proceed after launch screen disappears? thanks.

1) use following code in case if want set rootcontroller app delegate . use check if currentuser.uid not nil , matched values in database perform following code in didfinishlaunchingwithoptions of appdelegate . used me

            func application(_ application: uiapplication, didfinishlaunchingwithoptions launchoptions: [uiapplicationlaunchoptionskey: any]?) -> bool {     // override point customization after application launch.      firebaseapp.configure()     gidsignin.sharedinstance().clientid = firebaseapp.app()?.options.clientid        if let uid = auth.auth().currentuser?.uid {          database.database().reference().child("users").child(uid).observesingleevent(of: .value, with: { snapshot in             if snapshot.exist() {                 let storyboard = uistoryboard.init(name: "main", bundle: nil)                 let vc = storyboard.instantiateviewcontroller(withidentifier: "feedcontroller") as! feedcontroller                  self.window?.rootviewcontroller=vc                 self.window?.makekeyandvisible()             }             else {                 //present logincontroller here             }         })      }      return true } 

2) method: when had initialised logincontroller instead of calling function appdelegate or code in launchapplication. make function in login class , write following code when required parameters matched

 var transition: uiviewanimationoptions = .transitionflipfromleft let rootviewcontroller: uiwindow = ((uiapplication.shared.delegate?.window)!)!         rootviewcontroller.rootviewcontroller = self.storyboard?.instantiateviewcontroller(withidentifier: "rootnav")//rootnav storyboard id of naviagtioncontroller attached destinationcontroller [feedcontroller]         let mainwindow = (uiapplication.shared.delegate?.window!)!         mainwindow.backgroundcolor = uicolor(hue: 0.6477, saturation: 0.6314, brightness: 0.6077, alpha: 0.8)         uiview.transition(with: mainwindow, duration: 0.55001, options: transition, animations: { () -> void in         }) { (finished) -> void in          }