Function duplicating in Swift causing figure to double inappropriately - ios

Question

I'm currently attempting to pull a series of items from my database, and append them into an array stored within a variable.
This works successfully - and once the viewDidLoad executes.
I then want to call a function which iterates through this array, and for each element in it, pull out a balance and add it to a global variable.
I can do this by calling the function inside my initial database call, and wrapping it in DispatchQueue, however - it's duplicating, and actually doubling the value, almost like the add function is being called twice.
But I can't see where this is happening, or why. My understanding is that this database call only occurs once, but it seems like the function is getting called twice.
Particularly, my problem is happening like follows:
totalBalance is equal to 0 while the database call resolves
database call finds two entries, saves them to accounts variable
calculateBalance finds first balance of 2, second balance of 3 and adds together, updating totalBalance variable to 5
calculateBalance gets called again, adding 2 and 3 to totalBalance and equalling 10
totalBalance should equal 5, but it gets 2 + 3 twice, so ends up as being 10.
Here's my code:
class DashboardViewController: UIViewController {
let db = Firestore.firestore()
var accounts: [Account] = []
var totalBalance: Int = 0
#IBOutlet weak var tableView: UITableView!
#IBOutlet weak var balanceLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
fetchAccounts()
}
func fetchAccounts() {
db.collection("accounts")
.getDocuments { (QuerySnapshot, error) in
if let err = error {
print("Error getting documents: \(err)")
} else {
if let snapshotDocuments = QuerySnapshot?.documents {
for doc in snapshotDocuments {
let data = doc.data()
if let balance = data["accountBalance"] as? String {
let newAccount = Account(
accountBalance: balance,
)
self.accounts.append(newAccount)
}
DispatchQueue.main.async {
self.calculateBalance()
self.tableView.reloadData()
}
}
}
}
}
}
func calculateBalance() {
for cash in accounts {
totalBalance += Int(cash.accountBalance)!
}
DispatchQueue.main.async {
self.balanceLabel.text = "Overall balance - -£\(self.totalBalance)"
}
}
}
Any feedback here would be really appreciated - been scratching my head but think someone coming in from the outside will be able to spot what my problem is.

Answer 1

If I'm reading this correctly, you're calling the calculateBalance method in a loop, if you had 5 accounts in snapshotDocuments the method would get called 5 times:
for doc in snapshotDocuments {
let data = doc.data()
if let balance = data["accountBalance"] as? String {
let newAccount = Account(
accountBalance: balance,
)
self.accounts.append(newAccount)
}
//This will get called multiple times
//DispatchQueue.main.async {
// self.calculateBalance()
// self.tableView.reloadData()
//}
}
//This will get called only once
DispatchQueue.main.async {
self.calculateBalance()
self.tableView.reloadData()
}