How to decide what view to display based on global variable - swift

Question

I'm trying to implement an IOS swift app which starts off with a tab bar controller, and in one of the tab bar controllers is an item called "account".
When a user presses the account item, I want the app to decide (onclick event) whether the view that contains sign up/login is displayed or the profile view is displayed based on a global variable "loggedIn" (bool type).
(I've tried navigation controller but what I've understood from that is that it is a sequence of views which can't decide between views)
I want to know how can this be implemented, maybe some kind of "router" if you may that can switch between views...
If you didn't understand here's a picture of what I'm trying to implement
Basic Map of what I'm trying to explain
If you can suggest a more professional way of doing such design please don't hesitate to express your opinion.

Answer 1

I believe a good approach is updating the view controller when loggedIn status changes. If you don't already have, create a class inheriting from UITabBarController to manage your tabs. Here's the code:
class TabController: UITabBarController {}
In your storyboard, select your tab controller, go to the Identity Inspector and set TabController as the custom class. Now TabController will manage all the view controllers in your tab bar.
It's usually not a good approach to use global variables, so let's add loggedIn in the scope of TabController and listen for any of changes in it and update the corresponding view controller:
class TabController: UITabBarController {
var loggedIn = true {
didSet {
updateProfileTab()
}
}
}
Now, whenever you change loggedIn, that change will update the proper tab. Now let's write updateProfileTab():
class TabController: UITabBarController {
func updateProfileTab() {
let viewController: UIViewController
if loggedIn {
viewController = makeProfileViewController()
} else {
viewController = makeLoginViewController()
}
setViewController(viewController, at: 2)
}
func makeProfileViewController() -> ProfileViewController {
// create and return the profile view controller
}
func makeLoginViewController() -> LoginViewController {
// create and return the profile view controller
}
}
Naturally, you might want to write the body of both makeProfileViewController and makeLoginViewController methods. The last thing for TabController is to write setViewController(_:at:) method:
class TabController: UITabBarController {
...
func setViewController(_ viewController: UIViewController, at index: Int) {
let tabBarItem = viewControllers?[index].tabBarItem
viewController.tabBarItem = tabBarItem
viewControllers?[index] = viewController
}
...
}
Now, since TabController manages your tab bar, you can access it from within any of its children view controllers:
guard let tabController = tabBarController as? TabController else { return }
tabController.loggedIn = ...
Also, it's important to select the initial state. So, in the viewDidLoad from one of your tabbed view controllers, you should perform the above code. The first tab (the one that displays first) is probably the best place to do that. Hope this helps!
EDIT
To create your login and signup view controllers, the easiest way to go is by assigning ids in your storyboard. To do that, go to your storyboard, select the view controller, and in the Identity Inspector set a Storyboard ID, which you will use to instantiate the view controller:
func makeProfileViewController() -> ProfileViewController {
let controller = self.storyboard!.instantiateViewController(withIdentifier: "theStoryboardID")
return controller as! ProfileViewController
}
Note that I'm using force unwrap here (!). That's just for brevity. In a real case scenario you will want to use some if let or guard let statements to handle nil values.