Labels in viewcontroller are populated very slow - ios

Question

I'm struggling with extreme slow population of the labels in my viewcontroller.
The script sends a userid to a php script. To script retrieves data related to the userid in an array and sends it back as a json response to my app. Then the labels in my viewcontroller are populated with the corresponding data from the json array (dictionary).
the print statements in the "do{}" are executed immediately in the console, but the population of the labels in the viewcontroller takes ages. Putting self.lblStreet.text = self.loadedStreet outside do{}, but still in the task, it gives the same slow result.
class CharDetailViewController: UIViewController {
//Outlets
#IBOutlet weak var lblUID: UILabel!
#IBOutlet weak var lblStreet: UILabel!
//URL to our web service
let URL_GET_DETAILS = "http://somesite.com/script.php"
var passedUID: String!
var loadedStreet: String!
override func viewDidLoad() {
super.viewDidLoad()
let url = URL(string: URL_GET_DETAILS)
lblUID.text = passedUID
let request = NSMutableURLRequest(url: url! as URL)
request.httpMethod = "POST";
let sendUID = lblUID.text
let postParameters = "sendUID="+sendUID!;
request.httpBody = postParameters.data(using: String.Encoding.utf8)
let task = URLSession.shared.dataTask(with:request as URLRequest){
data, response, error in
if error != nil{
print("error is \(error)")
return;
}
do{
let myJSON = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary
if let parseJSON = myJSON {
var uid : String!
uid = parseJSON["userid"] as! String?
self.loadedStreet = parseJSON["street"] as! String!
self.lblStreet.text = parseJSON["street"] as! String!
print(uid)
print(self.loadedStreet)
}
}
catch {
print(error)
}
}
task.resume()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
}

Answer 1

Update your UI on the main thread. URLSession has you in a background thread. The appropriate code in Swift 3 is
DispatchQueue.main.async {
//your UI code
}
So your code should look more like this.
class CharDetailViewController: UIViewController {
//Outlets
#IBOutlet weak var lblUID: UILabel!
#IBOutlet weak var lblStreet: UILabel!
//URL to our web service
let URL_GET_DETAILS = "http://somesite.com/script.php"
var passedUID: String!
var loadedStreet: String!
override func viewDidLoad() {
super.viewDidLoad()
let url = URL(string: URL_GET_DETAILS)
lblUID.text = passedUID
let request = NSMutableURLRequest(url: url! as URL)
request.httpMethod = "POST";
let sendUID = lblUID.text
let postParameters = "sendUID="+sendUID!;
request.httpBody = postParameters.data(using: String.Encoding.utf8)
let task = URLSession.shared.dataTask(with:request as URLRequest){
data, response, error in
if error != nil{
print("error is \(error)")
return;
}
do{
let myJSON = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary
if let parseJSON = myJSON {
var uid : String!
uid = parseJSON["userid"] as! String?
DispatchQueue.main.async {
//your UI code
self.loadedStreet = parseJSON["street"] as! String!
self.lblStreet.text = parseJSON["street"] as! String!
}
print(uid)
print(self.loadedStreet)
}
}catch {
print(error)
}
}
task.resume()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
}

Answer 2

You shouldn't edit the UI anywhere other than the main thread. You can use this code to get the main thread in order to implement UI updates.
dispatch_async(dispatch_get_main_queue(), ^{
// Update UI stuff here
});