Firebase won't jump inside methods

Question

For some reason my firebase methods do things that make no sense to me. I want to login with a user and afterwards check on some data to make a decision. Both methods signIn() and getDocument() don't go beyond the curly brackets. If I set a breakpoint or step over the next point where it stops is outside the curly brackets. What am I doing wrong?

This is the whole code:

import Foundation
import Firebase

//@objc(LoginViewController)
class LoginViewController: UIViewController {

    @IBOutlet weak var errorMessage: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBOutlet weak var emailField: UITextField!
    @IBOutlet weak var passwordField: UITextField!

    @IBAction func didTapEmailLogin(_ sender: UIButton) {

        // Check if empty
        guard emailField.text != nil, passwordField.text != nil else {
            self.errorMessage.text = "Fields can't be empty."
            return
        }

        // Log in
        let email = emailField.text!
        let password = passwordField.text!
        guard login(with: email, with: password) else {
            print("Login didn't work")
            return
        }

        // Check if user has a group yet
        guard userHasGroup() else {
            print("Getting data didn't work")
            return
        }
    }

    func userHasGroup() -> Bool {
        var succesful = true
        let db = Firestore.firestore()
        let userUid = Auth.auth().currentUser?.uid
        let docRef = db.collection("users").document(userUid!)
        docRef.getDocument { (document, _) in
            if let document = document, document.exists {
                // Test
                print(document.data() as! [String: Any])
            } else {
                succesful = false
            }
        }
        return succesful
    }

    func login(with email: String, with password: String) -> Bool {
        var succesful = true
        Auth.auth().signIn(withEmail: email, password: password) { (user, error) in
            guard error == nil, user != nil else {
                // There was an error.
                self.errorMessage.text = "Email/password incorrect."
                succesful = false
                return
            }
        }
        return succesful
    }
}

Answer 1

This is the definition of async behaviour. The first time through your function all the code outside the closure is executed. Then when this async call to signIn returns the code inside the closure is executed.

The problem is the structure of your function. You can't reliably return a value from a function that contains a closure as the value won't be set when the function returns.

You need to change your function to use a completion handler.

I've posted a recent example of how to do this here Why aren't my Firebase Storage URLs uploading to Google Cloud Firestore?

Answer 2

So indeed it was an async problem.

This is how I made it work:

  @IBAction func didTapEmailLogin(_ sender: UIButton) {

    // Check if empty
    guard emailField.text != nil, passwordField.text != nil else {
        self.errorMessage.text = "Fields can't be empty."
        return
    }

    let email = emailField.text!
    let password = passwordField.text!

    loginAsync(with: email, with: password) { (loginSuccesful) in
        if loginSuccesful {
            self.userHasGroupAsync(completionHandler: { (hasGroup) in
                if hasGroup {
                    self.performSegue(withIdentifier: "fromLoginToHome", sender: self)
                } else {
                    self.performSegue(withIdentifier: "fromLoginToCreateJoinGroup", sender: self)
                }
            })
        }
    }
}

func loginAsync(with email: String, with password: String, completionHandler: @escaping (Bool) -> ()) {
    var succesful = true
    Auth.auth().signIn(withEmail: email, password: password) {
        (user, error) in
        guard error == nil, user != nil else {
            // There was an error.
            self.errorMessage.text = "Email/password incorrect."
            succesful = false
            return
        }
        completionHandler(succesful)
    }
}

func userHasGroupAsync(completionHandler: @escaping (Bool) -> ()) {
    var hasGroup = false
    let db = Firestore.firestore()
    let userUid = Auth.auth().currentUser?.uid
    let docRef = db.collection("users").document(userUid!)
    docRef.getDocument { (document, _) in
        if let document = document, document.exists {
            let data: [String: Any] = document.data()!
            let group = data["group"] as! String
            if group != "" { hasGroup = true }
        }
        completionHandler(hasGroup)
    } 
}