Assign username value from firestore

Question

i'm creating my first app (and newbie in swift). When i login from Facebook, the name and email are saved in Firestore. I'm trying to set the name from facebook to a variable to use it in other places, but i can't assign the value, always shows "nil" in the console. Anyone can help me please?

1. I set the variable

var userN: String?

2. I get the data from Firestore

func readDatabase(){

    let db = Firestore.firestore()
    let docRef = db.collection("users").document("email")


    docRef.getDocument { (document, error) in
        if let document = document, document.exists {
            let dataDescription = document.data().map(String.init(describing:)) ?? "nil"
            print("Document data: \(dataDescription)")

            let data = document.data()

            let userName = data!["name"]! as! String
            print(userName)

            let userEmail = data!["email"]! as! String
            print(userEmail)

let containerController = ContainerController()
            let containerController.userN = userName;
            return
        }
    }

}

i want to assign userN = userName, to use it in other view How can i do that? thanks

Answer 1

If you are using StoryBoards you can pass this through the segue function;

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "YourStoryBoardSegue" {
            if let viewController = segue.destination as? ContainerController {
                viewController.userN = userName
            }    
        }
   }

otherwise, best practice would be to use a delegate method.

Search stack overflow for best practices using delegates to pass data.

Answer 2

The question is extremely broad and without knowing details the only way to address it is with a general answer that specifically addresses how to read data from Firestore and save it in a variable to be used later.

Suppose your Firestore looks like this

root
   users
      uid_0
         name: "users name"
      uid_1
         name: "another users name"

and when the app loads, we want to read the users name and store it in in a variable per your question:

a variable to use it in other places

Here's what that could look like

class ViewController: NSViewController {

    var usersName = ""

    override func viewDidLoad() {
        super.viewDidLoad()
        FirebaseApp.configure()
        self.db = Firestore.firestore()
        let settings = self.db.settings
        self.db.settings = settings
        self.readUserName()
    }

    func readUsersName() {
        let users = self.db.collection("users")
        let thisUser = users.document("uid_1")
        thisUser.getDocument(completion: { documentSnapshot, error in
            if let error = error {
                print(error.localizedDescription)
                return
            }
            let name = documentSnapshot?.get("name") as! String
            self.usersName = name
        })
    }

The code sets up Firestore, reads the user name from the uid_1 document and stores it in a variable where it could be used later.

Suppose we want to let the user change their name. There's 100 ways to do it; passing data via a segue, use a delegate method or open a detail view controller and before it closes, have this master controller read the updated name from a textField and save the data. You could even pass the users uid and then in the detail viewcontroller read the document via that uid and then update it upon closing. However, all of those go beyond the scope of the question.