How get Realm result of objects in background queue, then use it on main thread

Question

I'm new in Realm. I have db Reaml and show some data from db to Tableview.

My code:

class MyRealmObject: Object {
@objc dynamic var id = 0
@objc dynamic var name = ""
@objc dynamic var favorite = false}

class MyViewController: UIViewController, ... {
    let realm = try! Realm()
    var objectsResult: Results<MyRealmObject>!
    ...
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)

    cell.textLabel?.text = objectsResult[indexPath.row].name
    ...

    return cell
}

func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
    //searching block
    ...
    DispatchQueue.global().async {
        autoreleasepool{
            let realm = try! Realm()
            var newObjectsResult: Results< MyRealmObject>!
            newObjectsResult = realm.objects(Objects.self).sorted(byKeyPath: "name", ascending: true).filter("name beginswith[cd] %@", searchText)
            objectsResult = newObjectsResult
            DispatchQueue.main.async {
                self.tableView.reloadData()
            }
        }
    }

}

In this case I got this error:

2018-09-22 14:42:48.262734+0800 TestApp[1194:338211] *** Terminating app due to uncaught exception 'RLMException', reason: 'Realm accessed from incorrect thread.'

How I can use realm objects from background thread to main thread for reloading my tableview?

Answer 1

You need to pass the instances across threads to the main thread. You can do this by using a ThreadSafeReference object. The Realm documentation contains an example:

let person = Person(name: "Jane")
try! realm.write {
    realm.add(person)
}
let personRef = ThreadSafeReference(to: person)
DispatchQueue(label: "background").async {
    autoreleasepool {
        let realm = try! Realm()
        guard let person = realm.resolve(personRef) else {
            return // person was deleted
        }
        try! realm.write {
            person.name = "Jane Doe"
        }
    }
}