Modifications to the layout engine must not be performed from a background thread after it has been accessed from the main thread in swift - swift

Question

I have given DispatchQueue.main.async {} where it necessary but when i give break point from dataTask here it says
Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Modifications to the layout engine must not be performed from a background thread after it has been accessed from the main thread.'
Cannot be called with asCopy = NO on non-main thread.
class EventsViewController: UIViewController {
#IBOutlet weak var backBtn: UIButton!
var eventsListArray = [AnyObject]()
var eventType: String?
var eventList : EventsModel? = nil
#IBOutlet weak var eventsTableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
getAllEventsList()
}
func getAllEventsList() {
DispatchQueue.main.async {
let deviceId: String = (UIDevice.current.identifierForVendor?.uuidString)!
let personalId: String = UserDefaults.standard.string(forKey: "regUserID") ?? ""//KeychainWrapper.standard.string(forKey: "USERID") ?? ""
let headers = ["deviceid": deviceId,"userType": "personal","key": personalId]
DispatchQueue.main.async {
let string = Constants.GLOBAL_URL + "/get/allevents"
var urlComponents = URLComponents(string: string)
let eventStatus = self.eventType
let requestEventType = URLQueryItem(name: "eventstatus", value: eventStatus)
urlComponents?.queryItems = [requestEventType]
let urlStr = urlComponents?.url
let request = NSMutableURLRequest(url: urlStr!, cachePolicy: .useProtocolCachePolicy,timeoutInterval: 10.0)
request.httpMethod = "POST"
request.allHTTPHeaderFields = headers as! [String : String]
let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
if error == nil {
let httpResponse = response as? HTTPURLResponse
if httpResponse!.statusCode == 200 {
do {
let jsonObject = try JSONSerialization.jsonObject(with: data!, options: .mutableLeaves) as! [String :AnyObject]
print("publish event \(jsonObject)")
self.eventList = EventsModel.init(fromDictionary: jsonObject)
DispatchQueue.main.async {
if self.eventList?.events.count != 0 {
DispatchQueue.main.async {
self.eventsTableView.reloadData()
}
}
else {
DispatchQueue.main.async {
Constants.showAlertView(alertViewTitle: "", Message: "No Events \(self.eventType)", on: self)
self.eventList?.events.removeAll()
self.eventsTableView.reloadData()
}
}
}
} catch { print(error.localizedDescription) }
} else {
Constants.showAlertView(alertViewTitle: "", Message: "Something went wrong, Please try again", on: self)
}
}
})
dataTask.resume()
}
}
}
}

Answer 1

You've probably missed a few spots where you're trying to present an alert when errors are thrown. Why don't you just enter the main queue right after the data request is complete.
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
DispatchQueue.main.async {
if error == nil {
//...
}
}
})