Understanding Tab Bar Controllers in iOS

Overview of Tab Bar Controllers

In iOS, a tab bar controller is a type of navigation view that allows users to navigate between multiple view controllers using a tab bar. The tab bar provides a visual indication of the different view controllers and their corresponding icons.

When you configure a tab bar controller, you create separate view controllers for each tab and assign them to the respective navigation views. The tab bar controller then manages the flow of navigation between these view controllers.

Configuring Tab Bar Controllers in AppDelegate

In your example, you’re trying to configure a tab bar controller in your AppDelegate. You’ve created multiple view controllers (VC1, VC2, etc.) and assigned them to their respective navigation views. However, when you try to set the tabBarController as the root view controller of your window, it doesn’t display the tab bar.

To resolve this issue, we need to understand how iOS manages its view hierarchy and how tab bar controllers fit into this hierarchy.

The View Hierarchy

In iOS, the view hierarchy is established by creating a chain of UIView instances that represent the layout of your application’s user interface. When you create a window in your app delegate, it becomes the root view controller of your application.

The window instance is then managed by the UIApplication instance, which in turn is managed by the UIApplicationDelegate protocol implemented by your app delegate.

// App Delegate (your app's entry point)
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Create the main window and set its root view controller to your tab bar controller
        let window = UIWindow(frame: UIScreen.main.bounds)
        self.window = window

        // Set up your tab bar controller
        let tabBarController = UITabBarController()
        // ...

        // Add the tab bar controller as a child of the main window's root view
        self.window?.rootViewController = tabBarController

        return true
    }
}

In this example, tabBarController is set as the root view controller of the window instance. However, when you create separate navigation views for each view controller (VC1Navigation, VC2Navigation, etc.), they become child views of the tabBarController.

The problem arises because the window instance’s root view controller is set to a single view controller (tabBarController) instead of its child views.

Resolving the Issue

To resolve this issue, you need to create a single parent view controller that manages all your tab bar controllers. This parent view controller will become the root view controller of the window instance.

Here’s an updated example:

// AppDelegate (your app's entry point)
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Create the main window and set its root view controller to your parent view controller
        let window = UIWindow(frame: UIScreen.main.bounds)
        self.window = window

        // Create a parent view controller that manages all tab bar controllers
        let parentViewController = UITabBarController()

        // Add each navigation view as a child of the parent view controller
        let VC1Navigation = UINavigationController(rootViewController: UIViewController())
        VC1Navigation.tabBarItem.image = UIImage(named: "Home.Re.png")
        parentViewController.addViewController(VC1Navigation)

        // ...

        // Set up your tab bar controller
        self.window?.rootViewController = parentViewController

        return true
    }
}

In this updated example, parentViewController is a single view controller that manages all the separate navigation views. The window instance’s root view controller is set to parentViewController, which in turn becomes the root view controller of your application.

This should resolve the issue and display the tab bar as expected.

Last modified on 2023-08-23