Check if user is logged in: Firebase iOS Swift 4 - firebase

Question

I am still having difficulty in checking whether the user is logged in with Google or Facebook to read and write on Firebase Database. I want to present a log in screen to a first time user and when the user authenticates, the log in screen is dismissed and it sent to the tabViewControllers. Here's my Swift 4 code below, which is placed in the AppDelegate, application(application:didFInishLaunchingWithOptions launchOptions:).
if Auth.auth().currentUser == nil {
print("NO USER") // this does print out in the console before the app crashes
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let loginVC = storyboard.instantiateViewController(withIdentifier: "loginVC") as! LogInViewController
self.window?.rootViewController = loginVC
} else {
let tabController = window!.rootViewController as! UITabBarController
if let tabViewControllers = tabController.viewControllers {
// First tab (only one so far...)
let navController = tabViewControllers[0] as! UINavigationController
let controller1 = navController.viewControllers.first as! UserProfileViewController
controller1.coreDataStack = coreDataStack
}
}
}
Please note the LogInViewController Scene is created in the Main.storyboard file and it has a Storyboard ID of "loginVC". When I try to run this, the program crashes at the part where the tabViewController[0] tries to fetch from the coreDataStack.

Answer 1

Hi you need to store UID of the user here is my code for login screen as you said if user open app for first time he have to login / authenticate and second time is automatically.
override func viewDidLoad() {
super.viewDidLoad()
if let uid = KeychainWrapper.standard.string(forKey: KEY_UID) {
autoLoginWithUID(uid: uid)
}
}
after app launches try it to auto login him if have stored his UID otherwise screen stays
func autoLoginWithUID(uid: String) {
KeychainWrapper.standard.set(uid, forKey: KEY_UID)
print(uid)
//Keep db and userRef as class constants shouldn't be here
let db = Firestore.firestore()
let userRef = db.collection("Users").document(uid)
userRef.getDocument { (document, error) in
if let document = document {
print("User data: \(document.data())")
self.performSegue(withIdentifier: "LogIn", sender: nil)
} else {
print("User does not exist")
}
}
}
Here I look in db if I have user with this UID if I got it its stored in global variable and continue. You can also store users credentials and log user by them. But dont know which way is more secure.
Auth.auth().signIn(with: credential) { (user, error) in
if let error = error {
// ...
return
}
// User is signed in
// ...
}
}
If you want more code from UserRequest let me know ;)