Using present in UIViewController properly - swift

Question

I encounter the problem that I cannot present a dynamic UIViewController in my class using "self". It tells me "Value of type '(LoginScreenVC) -> () -> (LoginScreenVC)' has no member 'view'".
It would work using a closure like e.g. if let loginScreen = UIStoryBoard ..., but since the UIViewController to switch to is dynamic, I cannot cast it to a specific UIViewController.
is there any other way to present the ViewController?
This is my code:
SWIFT 4.2 / XCode 10.1
import UIKit
class LoginScreenVC: UIViewController {
let myTokenHandler = TokenHandler()
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func loginButton(_ sender: Any) {
print("Login button pressed")
let usernameInputField = self.view.viewWithTag(6548) as! UITextField
let passwordInputField = self.view.viewWithTag(6549) as! UITextField
userInput = usernameInputField.text!
passInput = passwordInputField.text!
// call completion handler
requestToken(success: handlerBlock)
}
// completion handler step 1: request token and get redirect string to switch screen
func requestToken(success: (String) -> Void) {
let requestResult = myTokenHandler.requestToken(password: passInput, username: userInput)
success(requestResult)
}
// completion handler step 2: use redirect string to switch screen
let handlerBlock: (String) -> Void = { redirect in
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let loginScreen = storyboard.instantiateViewController(withIdentifier: redirect)
self.present(loginScreen, animated: true, completion: nil) //Value of type '(LoginScreenVC) -> () -> (LoginScreenVC)' has no member 'view'
}
}

Answer 1

You are saying:
let handlerBlock: (String) -> Void = { redirect in
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let loginScreen = storyboard.instantiateViewController(withIdentifier: redirect)
self.present(loginScreen, animated: true, completion: nil)
}
The problem is that you are using the term self in a context where there is no self. (Well, there is a self, but it isn't what you think.) present is a UIViewController instance method, so self needs to be a UIViewController instance; and in this context, it isn't.
I can think of half a dozen ways to express the thing you're trying to express, but the simplest would probably be to rewrite that as:
func handlerBlock(_ redirect:String) -> Void {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let loginScreen = storyboard.instantiateViewController(withIdentifier: redirect)
self.present(loginScreen, animated: true, completion: nil)
}
Now handlerBlock is an instance method, and self is meaningful — it is the instance, which is just what you want. The rest of your code is unchanged, because the bare name handlerBlock in the expression requestToken(success: handlerBlock) is a function name, just as before.