Why tableview datasource not changing from Realm Collection observer? - ios

Question

I have the request to realm database
func allContacts() -> Results<RMContact> {
let realm = self.encryptedRealm()
return realm!.objects(RMContact.self).sorted(byKeyPath: "lastActive", ascending: false)
}
And code from presenter
DispatchQueue.main.async {
let contacts = RMContactsManager.shared.allContacts()
self.notificationToken = contacts.observe { [weak self] (changes: RealmCollectionChange) in
guard let tableView = self?.view.tableView else { return }
switch changes {
case .initial:
UIView.performWithoutAnimation {
tableView.reloadData()
}
case .update(_, let deletions, let insertions, let modifications):
UIView.performWithoutAnimation {
tableView.beginUpdates()
tableView.insertRows(at: insertions.map({ IndexPath(row: $0, section: 0) }), with: .automatic)
tableView.deleteRows(at: deletions.map({ IndexPath(row: $0, section: 0)}), with: .automatic)
tableView.reloadRows(at: modifications.map({ IndexPath(row: $0, section: 0) }), with: .automatic)
tableView.endUpdates()
}
case .error(let error):
fatalError("\(error)")
}
}
}
After setting new lastActive value sequence in tableview didn't change
For the first time sorting is actual for the controller, but after setting new values to lastActive property no changes. Is it an observer problem?

Answer 1

The issue seems to be that you are getting changes in terms of insertions, deletions and modifications.
If you will first do the insertion and then deletion, (This is what you are doing right now), It will insert new values and the datasource will be modified so now when you delete the rows, it will not be correct.
Also in your case, where you are sorting the array, generally two elements will be replaced, one being deleted and other will be added.
So what can solve your problem is, first do deletions and then do insertions. Like this:
UIView.performWithoutAnimation {
tableView.beginUpdates()
tableView.deleteRows(at: deletions.map({ IndexPath(row: $0, section: 0)}), with: .automatic)
tableView.insertRows(at: insertions.map({ IndexPath(row: $0, section: 0) }), with: .automatic)
tableView.reloadRows(at: modifications.map({ IndexPath(row: $0, section: 0) }), with: .automatic)
tableView.endUpdates()
}