I am using Firestore to retrieve some data about a user and just update a label to be the user's first name on viewDidLoad of the Home screen. However, I learned the label was getting loaded/updated before even receiving the data.

I knew I had to wait until we fully received the data from Firestore. I feel like completion handlers were my best bet and I feel like I have followed Swift completion handler documentation to a T, but I can't seem to get it to work! If someone could please tell me what I am doing wrong here. One important thing to keep in mind here is before I make HomeViewController the rootview controller and present it to the user after logging in, I am retrieving the Google firestore DocumentReference and setting userProfileDoc to this reference to be used by the HomeViewController class in a different method.

class HomeViewController: UIViewController {
    var userProfileDoc: DocumentReference?
    private var currentUser: UserProfile?

    @IBOutlet weak var userFirstName: UILabel!
    @IBOutlet weak var logoutButton: UIButton!

    override func viewDidLoad() {
        super.viewDidLoad()

        let myCompletionHandler: (UserProfile) -> Void = { theUser in
            self.userFirstName.text = "Welcome, "   theUser.userFirstName!
            self.userFirstName.sizeToFit()
        }

        initializeUserProfile(using: myCompletionHandler)
    }

    func initializeUserProfile(using completionHandler: (UserProfile) -> Void) {
        self.currentUser = UserProfile(userProfileDoc!)

        completionHandler(self.currentUser!)
    }
}

`

Below is the constructor of UserProfile `

class UserProfile {
    var userFirstName: String?
    var userLastName: String?
    var profilePicURL: String?
    var UID: String?

    init(_ documentRef: DocumentReference) {
        documentRef.getDocument { [self] document, error in
            if let error = error as NSError? {
                print("Error getting document: \(error.localizedDescription)")
            }
            else {
                if let document = document {
                    let data = document.data()
                    userFirstName = data?["firstName"] as? String ?? ""
                    userLastName = data?["lastName"] as? String ?? ""
                    profilePicURL = data?["profilePicURL"] as? String ?? ""
                    UID = data?["uid"] as? String ?? ""
                }
            }
        }
    }
}

CodePudding user response：

Don't make the asynchronous call in the init but move it to initializeUserProfile instead and call the completion handler from inside the closure of the asynchronous call like below.

func initializeUserProfile(_ documentRef: DocumentReference, using completionHandler: (UserProfile) -> Void) {
    documentRef.getDocument { [self] document, error in
        if let error = error as NSError? {
            print("Error getting document: \(error.localizedDescription)")
        } else {
            if let document = document {
                let data = document.data()
                let userFirstName = data?["firstName"] as? String ?? ""
                let userLastName = data?["lastName"] as? String ?? ""
                let profilePicURL = data?["profilePicURL"] as? String ?? ""
                let userID = data?["uid"] as? String ?? ""
                completionHandler(UserProfile(userFirstName: userFirstName,
                                              userLastName: userLastName,
                                              profilePicURL: profilePicURL,
                                              UID: userID))
            }
        }
    }
}

and call it from viewDidLoad

initializeUserProfile(userProfileDoc, using: myCompletionHandler)

Note that I don't use Firebase myself so I haven't been able to compile the code given here but it should be enough to explain how I think this should be solved and this also mean I don't know if there are other improvements that should be done.

For completeness, this is how I changed the UserProfile class

class UserProfile {
    var userFirstName: String?
    var userLastName: String?
    var profilePicURL: String?
    var userID: String?

    init(userFirstName: String?, userLastName: String?, profilePicURL: String?, userID: String?) {
        self.userFirstName = userFirstName
        self.userLastName = userLastName
        self.profilePicURL = profilePicURL
        self.userID = userID
    }
}