Changed from Navigation to TabBar, CoreData does not load - swift

Question

I changed my Navigation Controller to Tab Bar Controller, then I wanted to compile the app. But it does not load my managedContext anymore.
This is my launching code when I load the app:
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
guard let navController = window?.rootViewController as? UINavigationController,
let viewController = navController.topViewController as? ViewController else {
return true
}
viewController.managedContext = coreDataStack.managedContext
// Override point for customization after application launch.
return true
}
Therefore I tried to edit the code like this:
Edit:
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let controller = storyboard.instantiateInitialViewController()
//let controller = storyboard.instantiateViewController(withIdentifier: "TabBarVC")
self.window?.rootViewController = controller
guard let tabController = window?.rootViewController as? UITabBarController,
let navController = tabController.viewControllers![0] as? UINavigationController,
let viewController = navController.topViewController as? ViewController else {
return true
}
// Version that works for UINavigationCOntroller
// guard let navController = window?.rootViewController as? UINavigationController,
// let viewController = navController.topViewController as? ViewController else {
// return true
// }
viewController.managedContext = coreDataStack.managedContext
// Override point for customization after application launch.
return true
}
I changed the code, but I still can not load managedContext, and it returns nil when I want to use it in ViewController, I also set the initial Viewcontroller to the tabBarController.

Answer 1

Set rootviewcontroller for your window first and then right your logic afterwards.
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
let storyboard = UIStoryboard(<StoryboardName>, bundle: nil)
let controller = storyboard.initializeInitialViewController()
window.rootViewController = controller
guard let navController = window?.rootViewController as? UITabBarController,
let viewController = navController.moreNavigationController as? ViewController else {
return true
}
viewController.managedContext = coreDataStack.managedContext
// Override point for customization after application launch.
return