Firebase .childAdded observer duplicating children - ios

Question

I am trying to have my program add every instance of a child to an array but whenever I delete a child then add another it duplicates that added child twice and if I do it again it will duplicate 3 times and so on depending on how many times I delete and add. The adding and deleting is mainly handled in the function below and I can't figure out why it is duplicating them.
func fetchContacts(completion: #escaping () -> ()){
contacts = [Contact]()
let userRef = ref.child("users").child(user).child("contacts")
userRef.observe(.childAdded, with: { (snapshot) in
if let dictionary = snapshot.value as? [String: AnyObject]{
print(snapshot)
let contact = Contact()
contact.setValuesForKeys(dictionary)
self.contacts.append(contact)
}
self.contactsTable.reloadData()
completion()
}, withCancel: nil)
userRef.observe(.childRemoved, with: { (snapshot) in
if let dictionary = snapshot.value as? [String: AnyObject]{
let contact = Contact()
contact.setValuesForKeys(dictionary)
if let i = self.contacts.index(where: { $0.name == contact.name }) {
self.contacts.remove(at: i)
}
}
self.contactsTable.reloadData()
completion()
}, withCancel: nil)
}
Here is where the deleting is handled and how the functions are called in the viewDidLoad:
override func viewDidLoad() {
contactsTable.delegate = self
contactsTable.dataSource = self
contactsTable.rowHeight = 65
super.viewDidLoad()
fetchContacts(){
self.contactsTable.reloadData()
}
}
func handleDelete(phone: String, completion: #escaping () -> ()){
let userRef = ref.child("users").child(user).child("contacts")
userRef.child(phone).removeValue { (error, ref) in
if error != nil {
print("Error: \(error)")
}
completion()
}
}

Answer 1

This may be to do with you not calling reloadData() on the main thread.
Instead of just:
self.contactsTable.reloadData()
try:
DispatchQueue.main.async {
self.contactsTable.reloadData()
}