Table view not showing data from realm database on first launch Swift - ios

Question

My goal is to display data fetched from realm database on the table view that I previously asynchronously added whenever I launch the app.
The problem is that when I first launch my app the table view doesn't show any data fetched from realm database but if I pull it to refresh the data is displayed.
Here is what I do in the following code:
I fetch data (contacts) from apple's contacts framework and pass them through a closure to a helper method where I:
Add them to realm database
fetch the contacts and store them in the data source array (setDataSource)
create the section titles for the table view
So far I made the debugging and noticed that the problem maybe with threading and concurrency, that is, on first launch the data is being added to realm asynchronously so when I fetch the contacts there's nothing to fetch.
Saying that, I haven't been able to solve the above identified problem so far because I don't know how to. I am learning to code with threading and concurrency and to use realm.
I've also seen some posts but in none of them were a similar problem.
I'd be very grateful for your help.
Thank you!
Table view controller:
override func viewDidLoad() {
super.viewDidLoad()
populateTableView() // TODO: Contacts don't show up on first launch of the app after installation.
}
func populateTableView() {
contactManager.populateDataSource(for: self)
tableView.reloadData()
}
Contact manager Class:
let store = CNContactStore()
let dataBase = DataBase()
var contactsDataSource = [[Contact]]()
var sectionTitles = [String]()
var deletedContactsDataSource = [[Contact]]()
var sectionTitlesForDeletedContactsTable = [String]()
func fetchUserContacts(completion: #escaping ContactsFetchingResult) {
print("Attempting to fetch contacts today...")
store.requestAccess(for: .contacts) { (granted, error) in
if let errorToCatch = error {
print("Failed to request access: ", errorToCatch)
} else if granted {
print("Access granted")
let keys = [CNContactGivenNameKey, CNContactFamilyNameKey, CNContactPhoneNumbersKey, CNContactThumbnailImageDataKey, CNContactImageDataAvailableKey, CNContactIdentifierKey, CNContactOrganizationNameKey]
let request = CNContactFetchRequest(keysToFetch: keys as [CNKeyDescriptor])
do {
try self.store.enumerateContacts(with: request, usingBlock: { (contact, stopPointerIfYouWantToStopEnumerating) in
completion(contact, nil)
})
} catch {
completion(nil, error)
}
} else {
print("Access denied")
}
}
}
func populateDataSource(for viewController: UIViewController?) {
fetchUserContacts { (result, error) in
if let errorToCatch = error {
guard let vc = viewController else { return }
UITableViewController.Alert.showFetchingErrorAlert(on: vc, message: errorToCatch.localizedDescription)
} else if let contact = result {
self.dataBase.insert(each: Contact(contact: contact, wasDeleted: false))
self.setDataSource()
self.setSectionTitles()
}
}
}
func setDataSource(from searchTerm: String = "") {
//Not deleted contacts
if !searching {
contactsDataSource = formatResults(from: dataBase.fetchContacts(), using: sectionTitles)
} else {
setDataSourceForFilteredContacts(from: searchTerm)
}
//Deleted contacts
deletedContactsDataSource = formatResults(from: dataBase.fetchDeletedContacts(), using: sectionTitlesForDeletedContactsTable)
}
func setSectionTitles() {
sectionTitles = generateSectionTitles(from: dataBase.fetchContacts())
sectionTitlesForDeletedContactsTable = generateSectionTitles(from: dataBase.fetchDeletedContacts())
}
Database:
func insert(each contact: Contact) {
let realm = try! Realm()
try! realm.write {
realm.add(contact, update: .modified)
}
}
func fetchContacts() -> Results<Contact> {
let realm = try! Realm()
return realm.objects(Contact.self).filter("wasDeleted = false").sorted(byKeyPath: "firstName", ascending: true)
}