Swift 3 - Declared variable giving me 'unresolved identifier error' - swift

Question

Im trying to use the securityCode variable in an if statement but its saying that its an 'unresolved identifier', any idea why?
heres my code:
func loginAction (sender: UIButton!){
guard let url = URL(string: "myurl") else{ return }
let session = URLSession.shared
session.dataTask(with: url) { (data, response, error) in
if let response = response {
print(response)
}
if let data = data {
print(data)
do {
let json = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as? NSDictionary
if let parseJSON = json {
let securityCode = parseJSON["security"] as? Bool
print("security code bool: \(String(describing: securityCode))")
}
} catch {
print(error)
}
}
}.resume()
if securityCode! == true {
let layout = UICollectionViewFlowLayout()
let mainScreen = MainController(collectionViewLayout: layout)
present(mainScreen, animated: true, completion: nil)
}
}

Answer 1

You need to read about scopes in Swift.
securityCode was declared inside this if statement:
if let parseJSON = json {
let securityCode = parseJSON["security"] as? Bool
print("security code bool: \(String(describing: securityCode))")
}
So, only the code inside the scope of this if statement will be aware of securityCode.
If you want the code after this if statement to be aware of securityCode you need to make its declaration outside of that scope, and this can be achieved like this:
var securityCode: Bool?
if let parseJSON = json {
securityCode = parseJSON["security"] as? Bool
print("security code bool: \(String(describing: securityCode))")
}

Answer 2

if securityCode! == true {
let layout = UICollectionViewFlowLayout()
let mainScreen = MainController(collectionViewLayout: layout)
present(mainScreen, animated: true, completion: nil)
}
This is out of scope.
To make it work, you have to embed the function into the same scope. For example,
if let parseJSON = json {
let securityCode = parseJSON["security"] as? Bool
print("security code bool: \(String(describing: securityCode))")
if let securityCode = securityCode{
if securityCode == true {
let layout = UICollectionViewFlowLayout()
let mainScreen = MainController(collectionViewLayout: layout)
self.present(mainScreen, animated: true, completion: nil)
}
}
}
Or declare the variable outside session.