ios - Why I couldn't assign fetched values from Firestore to an array in Swift?

Question

I tried several times with various ways to assign the collected values of documents from firestore into an array. Unfortunately, I could't find a way to solve this issue. I attached the code that I recently tried to implement. It includes before Firestore closure a print statement which print the whole fetched values successfully. However, after the closure and I tried to print the same array and the result is an empty array.

I tried to implement this code

var hotelCities: [String] = []

func getCities() {
    db.collection("Hotels").getDocuments() { (querySnapshot,  err) in
        if let err = err {
            print("Error getting documents: (err)")
        } else {
            for document in querySnapshot!.documents {
                var found = false
                let documentDetails = document.data() as NSDictionary
                let location = documentDetails["Location"] as! NSDictionary
                let city = location["city"]!
                if (self.hotelCities.count == 0) {
                    self.hotelCities.append(String(describing: city))
                }
                else{
                    for item in self.hotelCities {
                        if item == String(describing: city){
                            found = true
                        }
                    }
                    if (found == false){
                        self.hotelCities.append(String(describing: city))
                    }
                }
            }
        }
        print(self.hotelCities)
    }
    print(self.hotelCities)
}

Answer 1

Waitting for answers