iOS swift 3.0 Json parsing and alert issue - swift

Question

I'm working on login form. I'm a fresher on iOS development.
After successful login, I want to show an alert after completion of json parsing. I've parsed Ngoid inside a do while block. Now I want to pass the value "Ngoid" to the next view controller so that it can be used to fetch the further data.
Main Problem: Here is the code I have written and it gives me error to write alert it on main thread only.
As I want the "Ngoid" value for further use there, so how should I write it and what is the correct way to execute the code?
Here is the code I have written:
#IBAction func loginbutton(_ sender: Any) {
let myUrl = NSURL(string: "http://www.shreetechnosolution.com/funded/ngo_login.php")
let request = NSMutableURLRequest(url:myUrl! as URL)
request.httpMethod = "POST"// Compose a query string
let postString = "uname=\(textfieldusername.text!)&password=\(textfieldpassword.text!)";
request.httpBody = postString.data(using: String.Encoding.utf8)
let task = URLSession.shared.dataTask(with: request as URLRequest){ data , response , error in
if error != nil
{
//let alert = UIAlertView()
let alert = UIAlertController(title: "Alert Box !", message: "Login Failed", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
return
}
// You can print out response object
print("*****response = \(String(describing: response))")
let responseString = NSString(data: data! , encoding: String.Encoding.utf8.rawValue )
if ((responseString?.contains("")) == nil) {
print("incorrect - try again")
let alert = UIAlertController(title: "Try Again", message: "Username or Password Incorrect", preferredStyle: .alert)
let yesAction = UIAlertAction(title: "Nochmalversuchen", style: .default) { (action) -> Void in
}
// Add Actions
alert.addAction(yesAction)
// Present Alert Controller
self.present(alert, animated: true, completion: nil)
}
else {
print("correct good")
}
print("*****response data = \(responseString!)")
do {
//create json object from data
if let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary {
if let email = json["UserName"] as? String,
let password1 = json["passowrd"] as? String {
print ("Found User id: called \(email)")
}
let msg = (json.value(forKey: "message") as! NSString!) as String
let id = (json.value(forKey: "NgoId") as! NSString!) as String
// let alert : UIAlertView = UIAlertView(title: "Alert box!", message: "\(msg!).",delegate: nil, cancelButtonTitle: "OK")
// alert.show()
self.alert = UIAlertController(title: "Alert Box!", message: "\(msg)", preferredStyle: .alert)
print("the alert\(self.alert)")
self.action = UIAlertAction(title: "OK", style: .default) { (action) -> Void in
let viewControllerYouWantToPresent = self.storyboard?.instantiateViewController(withIdentifier: "pass1") as! ViewControllerngodetails
viewControllerYouWantToPresent.temp1 = self.id
self.present(viewControllerYouWantToPresent, animated: true, completion: nil)
}
self.alert.addAction(self.action)
self.present(self.alert, animated: true, completion: nil)
}
}catch let error {
print(error)
}
}
task.resume()
}

Answer 1

A pro tip:
All your UI related tasks need to be done in the main thread. Here you are presenting the alert inside a closure which executes in a background thread, thats the problem. You need to call the main queue and present alert in that block.
EDIT:
Just put your alert code in this-
For Swift 3-
Get main queue asynchronously
DispatchQueue.main.async {
//Code Here
}
Get main queue synchronously
DispatchQueue.main.sync {
//Code Here
}

Answer 2

Every UI update has to be on main thread:
#IBAction func loginbutton(_ sender: Any) {
let myUrl = NSURL(string: "http://www.shreetechnosolution.com/funded/ngo_login.php")
let request = NSMutableURLRequest(url:myUrl! as URL)
request.httpMethod = "POST"// Compose a query string
let postString = "uname=\(textfieldusername.text!)&password=\(textfieldpassword.text!)";
request.httpBody = postString.data(using: String.Encoding.utf8)
let task = URLSession.shared.dataTask(with: request as URLRequest){ data , response , error in
if error != nil
{
DispatchQueue.main.async {
let alert = UIAlertController(title: "Alert Box !", message: "Login Failed", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
// Present Alert Controller
self.present(alert, animated: true, completion: nil)
}
return
}
// You can print out response object
print("*****response = \(String(describing: response))")
let responseString = NSString(data: data! , encoding: String.Encoding.utf8.rawValue )
if ((responseString?.contains("")) == nil) {
print("incorrect - try again")
DispatchQueue.main.async {
let alert = UIAlertController(title: "Try Again", message: "Username or Password Incorrect", preferredStyle: .alert)
let yesAction = UIAlertAction(title: "Nochmalversuchen", style: .default) { (action) -> Void in }
// Add Actions
alert.addAction(yesAction)
// Present Alert Controller
self.present(alert, animated: true, completion: nil)
}
}
else {
print("correct good")
}
print("*****response data = \(responseString!)"
do {
//create json object from data
if let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary {
if let email = json["UserName"] as? String,
let password1 = json["passowrd"] as? String {
print ("Found User id: called \(email)")
}
let msg = (json.value(forKey: "message") as! NSString!) as String
let id = (json.value(forKey: "NgoId") as! NSString!) as String
DispatchQueue.main.async {
self.alert = UIAlertController(title: "Alert Box!", message: "\(msg)", preferredStyle: .alert)
print("the alert\(self.alert)")
self.action = UIAlertAction(title: "OK", style: .default) { (action) -> Void in
let viewControllerYouWantToPresent = self.storyboard?.instantiateViewController(withIdentifier: "pass1") as! ViewControllerngodetails
viewControllerYouWantToPresent.temp1 = self.id
self.present(viewControllerYouWantToPresent, animated: true, completion: nil)
}
self.alert.addAction(self.action)
self.present(self.alert, animated: true, completion: nil)
}
}
}catch let error {
print(error)
}
}
task.resume()
}