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

Question

I just downloaded iOS 13 for my iPhone and the new Xcode. I wanted to test my app for iOS 13, but when I try to run my app it will give me a error after a few seconds. Error

Answer 1

Your network fetch code is almost right - you are reloading the table on the main queue but not stopping the activity indicator.

You just need to move that line inside the closure:

let downloadedData_user = try decoder.decode(Top_us.self, from: data)
    self.Top_Search = downloadedData_user.users
    DispatchQueue.main.async {
        self.tableView.reloadData()
        self.Indicator.stopAnimating()
    }

Note that by convention, properties should start with a lower case letter while classes should start with an upper case letter. Both should use camelCase, so Top_Search should be topSearch, Top_us should be TopUsers and Indicator should be indicator.

Answer 2

You should wrap handling error by DispatchQueue.main.async{}

func Download_ID() {
    let urlString = "https://www.instagram.com/\(self.username_String)/?__a=1"
    guard let url = URL(string: urlString) else { return }
    URLSession.shared.dataTask(with: url) { data, urlResponse, error in
        guard let data = data, error == nil, urlResponse != nil else {
            // Add DispatchQueue
            DispatchQueue.main.async {
              print(error)
            }
            return
        }
        do
        {
            let decoder = JSONDecoder()
            let downloadedData_user = try decoder.decode(Website.self, from: data)
            // your logic
            DispatchQueue.main.async {
               // update or reload table in here
            }
        } catch {
            // Add dispach_queue
            DispatchQueue.main.async {
              print(error)
            }
        }
    }.resume()
}

Answer 3

For anyone having problems pinning down the cause, try the following.

Click on your scheme (next to the stop button), then Edit Scheme.

Under Run -> Diagnostics you have to activate Main Thread Checker.

As indicated by the breakpoint that got added, your execution will now halt when you try to alter the UI on a non-main thread.