Best practices for Storyboard login screen handling clearing of data upon logout

Question

I m building an iOS app using a Storyboard  The root view controller is a Tab Bar Controller  I m creating the login logout process  and it s mostly working fine  but I ve got a few issues  I need to know the BEST way to set all this up   I want to accomplish the following    Show a login screen the first time the app is launched  When they login  go to the first tab of the Tab Bar Controller  Any time they launch the app after that  check if they are logged in  and skip straight to the first tab of the root Tab Bar Controller  When they manually click a logout button  show the login screen  and clear all the data from the view controllers    What I ve done so far is set the root view controller to the Tab Bar Controller  and created a custom segue to my Login view controller  Inside my Tab Bar Controller class  I check whether they are logged in inside the viewDidAppear method  and a perform the segue   self performSegueWithIdentifier   pushLogin  sender self     I also setup a notification for when the logout action needs to be performed    NSNotificationCenter defaultCenter  addObserver self selector  selector logoutAccount  name   logoutAccount  object nil    Upon logout  I clear the credentials from the Keychain  run  self setSelectedIndex 0  and perform the segue to show the login view controller again   This all works fine  but I m wondering  should this logic be in the AppDelegate  I also have two issues    The first time they launch the app  the Tab Bar Controller shows briefly before the segue is performed  I ve tried moving the code to viewWillAppear but the segue will not work that early  When they logout  all the data is still inside all the view controllers  If they login to a new account  the old account data is still displayed until they refresh  I need a way to clear this easily on logout    I m open to reworking this  I ve considered making the login screen the root view controller  or creating a navigation controller in the AppDelegate to handle everything    I m just not sure what the best method is at this point

User · Answer

EDIT  Add logout action     1  First of all prepare the app delegate file  AppDelegate h   import  lt UIKit UIKit h gt    interface AppDelegate   UIResponder  lt UIApplicationDelegate gt    property  strong  nonatomic  UIWindow  window   property  nonatomic  BOOL authenticated    end   AppDelegate m   import  AppDelegate h   import  User h    implementation AppDelegate  -  BOOL application  UIApplication   application didFinishLaunchingWithOptions  NSDictionary   launchOptions       User  userObj     User alloc  init       self authenticated    userObj userAuthenticated        return YES      2  Create a class named User   User h   import  lt Foundation Foundation h gt    interface User   NSObject  -  void loginWithUsername  NSString   username andPassword  NSString   password  -  void logout  -  BOOL userAuthenticated    end   User m   import  User h    implementation User  -  void loginWithUsername  NSString   username andPassword  NSString   password          Validate user here with your implementation        and notify the root controller       NSNotificationCenter defaultCenter  postNotificationName   loginActionFinished  object self userInfo nil      -  void logout         Here you can delete the account    -  BOOL userAuthenticated           This variable is only for testing        Here you have to implement a mechanism to manipulate this     BOOL auth   NO       if  auth            return YES             return NO      3  Create a new controller RootViewController and connected with the first view  where login button live  Add also a Storyboard ID   initialView    RootViewController h   import  lt UIKit UIKit h gt   import  LoginViewController h    protocol LoginViewProtocol  lt NSObject gt   -  void dismissAndLoginView    end   interface RootViewController   UIViewController   property  nonatomic  weak  id  lt LoginViewProtocol gt  delegate   property  nonatomic  retain  LoginViewController  loginView     end   RootViewController m   import  RootViewController h    interface RootViewController      end   implementation RootViewController   synthesize loginView   -  void viewDidLoad        super viewDidLoad          Do any additional setup after loading the view  typically from a nib     -  void didReceiveMemoryWarning        super didReceiveMemoryWarning          Dispose of any resources that can be recreated     -  IBAction loginBtnPressed  id sender          NSNotificationCenter defaultCenter  addObserver self                                              selector  selector loginActionFinished                                                    name   loginActionFinished                                                 object loginView        pragma mark - Dismissing Delegate Methods  - void  loginActionFinished  NSNotification  notification        AppDelegate  authObj    AppDelegate    UIApplication sharedApplication  delegate       authObj authenticated   YES        self dismissLoginAndShowProfile      -  void dismissLoginAndShowProfile        self dismissViewControllerAnimated NO completion            UIStoryboard  storyboard    UIStoryboard storyboardWithName   Main  bundle nil           UITabBarController  tabView    storyboard instantiateViewControllerWithIdentifier   profileView             self presentViewController tabView animated YES completion nil                 end   4  Create a new controller LoginViewController and connected with the login view   LoginViewController h   import  lt UIKit UIKit h gt   import  User h    interface LoginViewController   UIViewController   LoginViewController m   import  LoginViewController h   import  AppDelegate h   -  void viewDidLoad        super viewDidLoad      -  IBAction submitBtnPressed  id sender       User  userObj     User alloc  init           Here you can get the data from login form        and proceed to authenticate process     NSString  username     username retrieved through login form       NSString  password     password retrieved through login form        userObj loginWithUsername username andPassword password       end   5  At the end add a new controller ProfileViewController and connected with the profile view in the tabViewController   ProfileViewController h   import  lt UIKit UIKit h gt    interface ProfileViewController   UIViewController   end   ProfileViewController m   import  ProfileViewController h   import  RootViewController h   import  AppDelegate h   import  User h    interface ProfileViewController      end   implementation ProfileViewController  -  id initWithNibName  NSString   nibNameOrNil bundle  NSBundle   nibBundleOrNil       self    super initWithNibName nibNameOrNil bundle nibBundleOrNil       if  self               Custom initialization           return self     -  void viewDidLoad        super viewDidLoad       -  void  viewWillAppear  BOOL animated        super viewWillAppear animated        if    AppDelegate    UIApplication sharedApplication  delegate  authenticated              UIStoryboard  storyboard    UIStoryboard storyboardWithName   Main  bundle nil            RootViewController  initView     RootViewController   storyboard instantiateViewControllerWithIdentifier   initialView             initView setModalPresentationStyle UIModalPresentationFullScreen            self presentViewController initView animated NO completion nil         else             proceed with the profile view          -  void didReceiveMemoryWarning        super didReceiveMemoryWarning          Dispose of any resources that can be recreated     -  IBAction logoutAction  id sender       User  userObj     User alloc  init       userObj logout       AppDelegate  authObj    AppDelegate    UIApplication sharedApplication  delegate      authObj authenticated   NO      UIStoryboard  storyboard    UIStoryboard storyboardWithName   Main  bundle nil       RootViewController  initView     RootViewController   storyboard instantiateViewControllerWithIdentifier   initialView        initView setModalPresentationStyle UIModalPresentationFullScreen       self presentViewController initView animated NO completion nil        end   LoginExample is a sample project for extra help

User · Answer

To update  iAleksandr answer for Xcode 11  which causes problems due to Scene kit   Replace   let appDelegate   UIApplication shared delegate as  AppDelegate appDelegate window  rootViewController   rootViewController   With guard let windowScene   UIApplication shared connectedScenes first as  UIWindowScene let sceneDelegate   windowScene delegate as  SceneDelegate         else   return   sceneDelegate window  rootViewController   rootViewController  call the Switcher updateRootViewcontroller in Scene delegate rather than App delegate like this   func scene   scene  UIScene  willConnectTo session  UISceneSession  options connectionOptions  UIScene ConnectionOptions    Switcher updateRootViewController    guard let      scene as  UIWindowScene  else   return

User · Answer

I had a similar issue to solve in an app and I used the following method  I didn t use notifications for handling the navigation   I have three storyboards in the app    Splash screen storyboard - for app initialisation and checking if the user is already logged in Login storyboard - for handling user login flow Tab bar storyboard - for displaying the app content   My initial storyboard in the app is Splash screen storyboard  I have navigation controller as the root of login and tab bar storyboard to handle view controller navigations   I created a Navigator class to handle the app navigation and it looks like this   class Navigator  NSObject          static func moveTo   destinationViewController  UIViewController  from sourceViewController  UIViewController  transitionStyle  UIModalTransitionStyle     crossDissolve  completion      - gt         nil                                  DispatchQueue main async                          if var topController   UIApplication shared keyWindow  rootViewController                                  while let presentedViewController   topController presentedViewController                                          topController   presentedViewController                                                                                                destinationViewController modalTransitionStyle    transitionStyle    nil                                  sourceViewController present destinationViewController  animated  true  completion  completion                                                          Let s look at the possible scenarios    First app launch  Splash screen will be loaded where I check if the user is already signed in  Then login screen will be loaded using the Navigator class as follows    Since I have navigation controller as the root  I instantiate the navigation controller as initial view controller   let loginSB   UIStoryboard name   splash   bundle  nil   let loginNav   loginSB instantiateInitialViewcontroller   as  UINavigationController  Navigator moveTo loginNav  from  self    This removes the slpash storyboard from app window s root and replaces it with login storyboard   From login storyboard  when the user is successfully logged in  I save the user data to User Defaults and initialize a UserData singleton to access the user details  Then Tab bar storyboard is loaded using the navigator method   Let tabBarSB   UIStoryboard name   tabBar   bundle  nil  let tabBarNav   tabBarSB instantiateInitialViewcontroller   as  UINavigationController  Navigator moveTo tabBarNav  from  self    Now the user signs out from the settings screen in tab bar  I clear all the saved user data and navigate to login screen   let loginSB   UIStoryboard name   splash   bundle  nil   let loginNav   loginSB instantiateInitialViewcontroller   as  UINavigationController  Navigator moveTo loginNav  from  self     User is logged in and force kills the app   When user launches the app  Splash screen will be loaded  I check if user is logged in and access the user data from User Defaults  Then initialize the UserData singleton and shows tab bar instead of login screen

User · Answer

In Xcode 7 you can have multiple storyBoards  It will be better if you can keep the Login flow in a separate storyboard    This can be done using SELECT VIEWCONTROLLER   Editor   Refactor to Storyboard  And here is the Swift version for setting a view as the RootViewContoller-       let appDelegate   UIApplication sharedApplication   delegate as  AppDelegate     appDelegate window  rootViewController   newRootViewController      let rootViewController  UIViewController   UIStoryboard name   Main   bundle  nil  instantiateViewControllerWithIdentifier  LoginViewController

User · Answer

I didn t like bhavya s answer because of using AppDelegate inside View Controllers and setting rootViewController has no animation  And Trevor s answer has issue with flashing view controller on iOS8   UPD 07 18 2015  AppDelegate inside View Controllers   Changing AppDelegate state  properties  inside view controller breaks encapsulation   Very simple hierarchy of objects in every iOS project   AppDelegate  owns window and rootViewController   ViewController  owns view   It s ok that objects from the top change objects at the bottom  because they are creating them  But it s not ok if objects on the bottom change objects on top of them  I described some basic programming OOP principle   DIP  Dependency Inversion Principle   high level module must not depend on the low level module  but they should depend on abstractions     If any object will change any object in this hierarchy  sooner or later there will be a mess in the code  It might be ok on the small projects but it s no fun to dig through this mess on the bit projects     UPD 07 18 2015  I replicate modal controller animations using UINavigationController  tl dr  check the project    I m using UINavigationController to present all controllers in my app  Initially I displayed login view controller in navigation stack with plain push pop animation  Than I decided to change it to modal with minimal changes    How it works    Initial view controller  or self window rootViewController  is UINavigationController with ProgressViewController as a rootViewController  I m showing ProgressViewController because DataModel can take some time to initialize because it  inits core data stack like in this article  I really like this approach   AppDelegate is responsible for getting login status updates  DataModel handles user login logout and AppDelegate is observing it s userLoggedIn property via KVO  Arguably not the best method to do this but it works for me   Why KVO is bad  you can check in this  or this article  Why Not Use Notifications  part   ModalDismissAnimator and ModalPresentAnimator are used to customize default push animation    How animators logic works    AppDelegate sets itself as a delegate of  self window rootViewController  which is UINavigationController   AppDelegate returns one of animators in - AppDelegate navigationController animationControllerForOperation fromViewController toViewController   if necessary  Animators implement -transitionDuration  and -animateTransition  methods  - ModalPresentAnimator animateTransition     -  void animateTransition  id lt UIViewControllerContextTransitioning gt  transitionContext       UIViewController  toViewController    transitionContext viewControllerForKey UITransitionContextToViewControllerKey         transitionContext containerView  addSubview toViewController view       CGRect frame   toViewController view frame      CGRect toFrame   frame      frame origin y   CGRectGetHeight frame       toViewController view frame   frame       UIView animateWithDuration  self transitionDuration transitionContext                       animations                   toViewController view frame   toFrame         completion   BOOL finished                   transitionContext completeTransition   transitionContext transitionWasCancelled                  Test project is here

User · Answer

Here is what I ended up doing to accomplish everything  The only thing you need to consider in addition to this is  a  the login process and  b  where you are storing your app data  in this case  I used a singleton      As you can see  the root view controller is my Main Tab Controller  I did this because after the user has logged in  I want the app to launch directly to the first tab   This avoids any  flicker  where the login view shows temporarily    AppDelegate m  In this file  I check whether the user is already logged in  If not  I push the login view controller  I also handle the logout process  where I clear data and show the login view   -  BOOL application  UIApplication   application didFinishLaunchingWithOptions  NSDictionary   launchOptions           Show login view if not logged in already     if   AppData isLoggedIn              self showLoginScreen NO              return YES     - void  showLoginScreen  BOOL animated           Get login screen from storyboard and present it     UIStoryboard  storyboard    UIStoryboard storyboardWithName   MainStoryboard  bundle nil       LoginViewController  viewController    LoginViewController    storyboard instantiateViewControllerWithIdentifier   loginScreen         self window makeKeyAndVisible        self window rootViewController presentViewController viewController                                              animated animated                                            completion nil      - void  logout          Remove data from singleton  where all my app data is stored       AppData clearData          Reset view controller  this will quickly clear all the views     UIStoryboard  storyboard    UIStoryboard storyboardWithName   MainStoryboard  bundle nil      MainTabControllerViewController  viewController    MainTabControllerViewController    storyboard instantiateViewControllerWithIdentifier   mainView        self window setRootViewController viewController          Show login screen     self showLoginScreen NO        LoginViewController m  Here  if the login is successful  I simply dismiss the view and send a notification   - void  loginWasSuccessful            Send notification        NSNotificationCenter defaultCenter  postNotificationName   loginSuccessful  object self            Dismiss login screen       self dismissViewControllerAnimated YES completion nil

User · Answer

I use this to check for first launch   -  NSInteger  checkForFirstLaunch       NSInteger result   0    no first launch         Get current version   Bundle Version   from the default Info plist file     NSString  currentVersion    NSString    NSBundle mainBundle  objectForInfoDictionaryKey   CFBundleVersion        NSArray  prevStartupVersions     NSUserDefaults standardUserDefaults  arrayForKey   prevStartupVersions        if  prevStartupVersions    nil                   Starting up for first time with NO pre-existing installs  e g   fresh            install of some version            NSUserDefaults standardUserDefaults  setObject  NSArray arrayWithObject currentVersion  forKey   prevStartupVersions            result   1    first launch of the app       else           if    prevStartupVersions containsObject currentVersion                            Starting up for first time with this version of the app  This                means a different version of the app was alread installed once                and started              NSMutableArray  updatedPrevStartVersions    NSMutableArray arrayWithArray prevStartupVersions                updatedPrevStartVersions addObject currentVersion                 NSUserDefaults standardUserDefaults  setObject updatedPrevStartVersions forKey   prevStartupVersions                result   2    first launch of this version of the app                         Save changes to disk       NSUserDefaults standardUserDefaults  synchronize        return result       if the user deletes the app and re-installs it  it counts like a first launch   In the AppDelegate I check for first launch and create a navigation-controller with the login screens  login and register   which I put on top of the current main window    self window makeKeyAndVisible    if  firstLaunch    1        UINavigationController   login     UINavigationController alloc  initWithRootViewController loginController        self window rootViewController presentViewController  login animated NO completion nil       As this is on top of the regular view controller it s independent from the rest of your app and you can just dismiss the view controller  if you don t need it anymore  And you can also present the view this way  if the user presses a button manually   BTW  I save the login-data from my users like this   KeychainItemWrapper  keychainItem     KeychainItemWrapper alloc  initWithIdentifier   com youridentifier  accessGroup nil    keychainItem setObject password forKey    bridge id  kSecValueData     keychainItem setObject email forKey    bridge id  kSecAttrAccount      For the logout  I switched away from CoreData  too slow  and use NSArrays and NSDictionaries to manage my data now  Logout just means to empty those arrays and dictionaries  Plus I make sure to set my data in viewWillAppear   That s it

User · Answer

In your appDelegate m inside your didFinishLaunchingWithOptions    authenticatedUser  check from NSUserDefaults User credential if its present then set your navigation flow accordingly  if  authenticatedUser         self window rootViewController     UIStoryboard storyboardWithName   Main  bundle  NSBundle mainBundle   instantiateInitialViewController             else       UIViewController  rootController     UIStoryboard storyboardWithName   Main  bundle  NSBundle mainBundle   instantiateViewControllerWithIdentifier   LoginViewController        UINavigationController  navigation     UINavigationController alloc  initWithRootViewController rootController        self window rootViewController   navigation      In SignUpViewController m file  -  IBAction actionSignup  id sender       AppDelegate  appDelegateTemp     UIApplication sharedApplication delegate        appDelegateTemp window rootViewController     UIStoryboard storyboardWithName   Main  bundle  NSBundle mainBundle   instantiateInitialViewController       In file MyTabThreeViewController m  -  IBAction actionLogout  id sender           Delete User credential from NSUserDefaults and other data related to user      AppDelegate  appDelegateTemp     UIApplication sharedApplication delegate        UIViewController  rootController     UIStoryboard storyboardWithName   Main  bundle  NSBundle mainBundle   instantiateViewControllerWithIdentifier   LoginViewController         UINavigationController  navigation     UINavigationController alloc  initWithRootViewController rootController       appDelegateTemp window rootViewController   navigation       Swift 4 Version  didFinishLaunchingWithOptions in app delegate assuming your initial view controller is the signed in TabbarController   if Auth auth   currentUser    nil           let rootController   UIStoryboard name   Main   bundle  Bundle main  instantiateViewController withIdentifier   WelcomeNavigation           self window  rootViewController   rootController            return true   In Sign up view controller    IBAction func actionSignup   sender  Any    let appDelegateTemp   UIApplication shared delegate as  AppDelegate appDelegateTemp  window  rootViewController   UIStoryboard name   Main   bundle  Bundle main  instantiateInitialViewController       MyTabThreeViewController     Remove user credentials guard let appDel   UIApplication shared delegate as  AppDelegate else   return           let rootController   UIStoryboard name   Main   bundle  Bundle main  instantiateViewController withIdentifier   WelcomeNavigation           appDel window  rootViewController   rootController

User · Answer

enter image description here  In App Delegate m   -  BOOL application  UIApplication   application didFinishLaunchingWithOptions  NSDictionary   launchOptions      Override point for customization after application launch    UIBarButtonItem appearance  setBackButtonTitlePositionAdjustment UIOffsetMake 0  -60                                                       forBarMetrics UIBarMetricsDefault    NSString  identifier  BOOL isSaved     NSUserDefaults standardUserDefaults  boolForKey   loginSaved    if  isSaved          identifier   homeViewControllerId       UIWindow  mainWindow    UIApplication sharedApplication  delegate  window       UITabBarController  tabBarVC         UIStoryboard storyboardWithName   Main  bundle nil  instantiateViewControllerWithIdentifier   TabBarVC        mainWindow rootViewController tabBarVC    else         identifier   loginViewControllerId       UIStoryboard      storyboardobj  UIStoryboard storyboardWithName   Main  bundle nil       UIViewController  screen    storyboardobj instantiateViewControllerWithIdentifier identifier        UINavigationController  navigationController   UINavigationController alloc  initWithRootViewController screen        self window rootViewController   navigationController       self window makeKeyAndVisible       return YES       view controller m In view did load  -  void viewDidLoad    super viewDidLoad      Do any additional setup after loading the view   UIBarButtonItem  barButton     UIBarButtonItem alloc  initWithTitle   Logout  style UIBarButtonItemStyleDone target self action  selector logoutButtonClicked      self navigationItem setLeftBarButtonItem barButton        In logout  button action  - void logoutButtonClicked  id sender   UIAlertController  alertController    UIAlertController alertControllerWithTitle   Alert  message   Do you want to logout   preferredStyle UIAlertControllerStyleAlert         alertController addAction  UIAlertAction actionWithTitle   Logout  style UIAlertActionStyleDefault handler   UIAlertAction  action               NSUserDefaults  defaults    NSUserDefaults standardUserDefaults        defaults setBool NO forKey   loginSaved                 NSUserDefaults standardUserDefaults  synchronize         AppDelegate  appDelegate    UIApplication sharedApplication  delegate      UIStoryboard      storyboardobj  UIStoryboard storyboardWithName   Main  bundle nil       UIViewController  screen    storyboardobj instantiateViewControllerWithIdentifier   loginViewControllerId         appDelegate window setRootViewController screen           alertController addAction  UIAlertAction actionWithTitle   Cancel  style UIAlertActionStyleDefault handler   UIAlertAction  action         self dismissViewControllerAnimated YES completion nil         dispatch async dispatch get main queue             self presentViewController alertController animated YES completion nil

User · Answer

Here s my Swifty solution for any future onlookers   1  Create a protocol to handle both login and logout functions   protocol LoginFlowHandler       func handleLogin withWindow window  UIWindow       func handleLogout withWindow window  UIWindow       2  Extend said protocol and provide the functionality here for logging out    extension LoginFlowHandler        func handleLogin withWindow window  UIWindow              if let     AppState shared currentUserId                 User has logged in before  cache and continue             self showMainApp withWindow  window            else                 No user information  show login flow             self showLogin withWindow  window                       func handleLogout withWindow window  UIWindow              AppState shared signOut            showLogin withWindow  window             func showLogin withWindow window  UIWindow             window  subviews forEach    0 removeFromSuperview             window  rootViewController   nil         window  rootViewController   R storyboard login instantiateInitialViewController           window  makeKeyAndVisible              func showMainApp withWindow window  UIWindow             window  rootViewController   nil         window  rootViewController   R storyboard mainTabBar instantiateInitialViewController           window  makeKeyAndVisible              3  Then I can conform my AppDelegate to the LoginFlowHandler protocol  and call handleLogin on startup   class AppDelegate  UIResponder  UIApplicationDelegate  LoginFlowHandler        var window  UIWindow       func application   application  UIApplication  didFinishLaunchingWithOptions launchOptions   UIApplicationLaunchOptionsKey  Any    - gt  Bool            window   UIWindow init frame  UIScreen main bounds           initialiseServices            handleLogin withWindow  window           return true            From here  my protocol extension will handle the logic or determining if the user if logged in out  and then change the windows rootViewController accordingly

User · Answer

Thanks bhavya s solution There have been two answers about swift  but those are not very intact  I have do that in the swift3 Below is the main code    In AppDelegate swift  func application   application  UIApplication  didFinishLaunchingWithOptions launchOptions   UIApplicationLaunchOptionsKey  Any    - gt  Bool          Override point for customization after application launch          seclect the mainStoryBoard entry by whthere user is login      let userDefaults   UserDefaults standard      if let isLogin  Bool   userDefaults value forKey Common isLoginKey  as  Bool            if   isLogin                self window  rootViewController   UIStoryboard name   Main   bundle  nil  instantiateViewController withIdentifier   LogIn                 else           self window  rootViewController   mainStoryboard instantiateViewController withIdentifier   LogIn             return true     In SignUpViewController swift   IBAction func userLogin   sender  UIButton          handle your login work     UserDefaults standard setValue true  forKey  Common isLoginKey      let delegateTemp   UIApplication shared delegate     delegateTemp  window   rootViewController   UIStoryboard name   Main   bundle  nil  instantiateViewController withIdentifier   Main       In logOutAction function   IBAction func logOutAction   sender  UIButton        UserDefaults standard setValue false  forKey  Common isLoginKey      UIApplication shared delegate  window   rootViewController   UIStoryboard name   Main   bundle  nil  instantiateInitialViewController

User · Answer

Doing this from the app delegate is NOT recommended  AppDelegate manages the app life cycle that relate to launching  suspending  terminating and so on  I suggest doing this from your initial view controller in the viewDidAppear  You can self presentViewController and self dismissViewController from the login view controller  Store a bool key in NSUserDefaults to see if it s launching for the first time

User · Answer

I m in the same situation as you and the solution I found for cleaning the data is deleting all the CoreData stuff that my view controllers rely on to draw it s info  But I still found this approach to be very bad  I think that a more elegant way to do this can be accomplished without storyboards and using only code to manage the transitions between view controllers    I ve found this project at Github that does all this stuff only by code and it s quite easy to understand  They use a Facebook-like side menu and what they do is change the center view controller depending if the user is logged-in or not  When the user logs out the appDelegate removes the data from CoreData and sets the main view controller to the login screen again

User · Answer

After creating the LoginViewController and TabBarController  we need to add a StoryboardID as    loginViewController    and    tabBarController    respectively   Then I prefer to create the Constant struct   struct Constants       struct StoryboardID           static let signInViewController    SignInViewController          static let mainTabBarController    MainTabBarController             struct kUserDefaults           static let isSignIn    isSignIn            In LoginViewController add IBAction    IBAction func tapSignInButton   sender  UIButton        UserDefaults standard set true  forKey  Constants kUserDefaults isSignIn      Switcher updateRootViewController       In ProfileViewController add IBAction    IBAction func tapSignOutButton   sender  UIButton        UserDefaults standard set false  forKey  Constants kUserDefaults isSignIn      Switcher updateRootViewController       In AppDelegate add line of code in didFinishLaunchingWithOptions   func application   application  UIApplication  didFinishLaunchingWithOptions launchOptions   UIApplicationLaunchOptionsKey  Any    - gt  Bool        Switcher updateRootViewController        return true     Finally create Switcher class   import UIKit  class Switcher        static func updateRootViewController              let status   UserDefaults standard bool forKey  Constants kUserDefaults isSignIn          var rootViewController   UIViewController            if DEBUG         print status           endif          if  status    true                let mainStoryBoard   UIStoryboard name   Main   bundle  nil              let mainTabBarController   mainStoryBoard instantiateViewController withIdentifier  Constants StoryboardID mainTabBarController  as  MainTabBarController             rootViewController   mainTabBarController           else               let mainStoryBoard   UIStoryboard name   Main   bundle  nil              let signInViewController   mainStoryBoard instantiateViewController withIdentifier  Constants StoryboardID signInViewController  as  SignInViewController             rootViewController   signInViewController                    let appDelegate   UIApplication shared delegate as  AppDelegate         appDelegate window  rootViewController   rootViewController             That is all

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