Checking Firebase current signed-in user via Listener in iOS

Question

I\'ve implement Firebase Authorization to login on my iOS app via Facebook and Google. I\'m coding Swift. When the app starts up I need to check whether a user is already si

Answer 1

I've implemented it like this:

FIRAuth.auth()?.addStateDidChangeListener { auth, user in
  if let user = user {
    // User is signed in. Show home screen
  } else {
    // No User is signed in. Show user the login screen
  }
}

If you don't need the User object after checking, you can replace if let user = user with a boolean test, like this:

FIRAuth.auth()?.addStateDidChangeListener { auth, user in
  if user != nil {
    // User is signed in. Show home screen
  } else {
    // No User is signed in. Show user the login screen
  }
}

Where to put the listener (from the comments):

For the cases I used to check if a user is signed in, it was enough to put it at the beginning of viewDidLoad in the specific view controller. But if you have any cases where you need to check every time you enter the specific view controller then it would be better to put it at the beginning of viewDidAppear. But I think in most cases you need to check only once, if the user enters the view

Answer 2

If you're setting up the StateDidChangeListener in application:didFinishLaunchingWithOptions, you'll notice that it fires once when the listener is attached (to set the initial state, which is nil when initialising) and then again once it's finished initialising (potentially not nil). This is intended behaviour, but really impractical if you're setting it up early.

An alternative to using the listener is using NotificationCenter. This will fire once initialisation has finished:

NotificationCenter.default.addObserver(forName: NSNotification.Name.AuthStateDidChange, object: Auth.auth(), queue: nil) { _ in
    let user = Auth.auth().currentUser
}