UIAlertController is not working in model class - ios

Question

I want to show an alert. But I want to show it by creating a function in another class and call that function from a viewcontroller. But it does not work.
Here is code from my LoginViewController:
class LoginViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
LoginModel().show_alert()
}
}
Here is code from my LoginModel:
class LoginModel{
let controller = LoginViewController()
public func show_alert(){
let alert = UIAlertController(title: "Title", message: "Some Message",
preferredStyle: UIAlertControllerStyle.alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler:
nil))
controller.present(alert, animated: true, completion: nil)
}
}

Answer 1

You need to pass the reference of UIViewController subclass to your LoginModel class, to present the UIAlertViewController on LoginViewController. You should call show alert once the LoginViewController view is appeared on the screen, move the call to ViewWillApear or viewDidApear method
final class LoginViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidApear(animated)
LoginModel().show_alert(on: self)
}
}
final class LoginModel {
public func show_alert(on vc: UIViewController) {
let alert = UIAlertController(title: "Title", message: "Some Message",
preferredStyle: UIAlertControllerStyle.alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler:
nil))
vc.present(alert, animated: true, completion: nil)
}
}
ideally you should not create the UI related methods in model classes, they should be on on UIViewController/UIView classes or their extension methods. Model classes should not know anything about UI stuff. So you can easily create simple extension method on UIViewController and call the showAlert method from viewController.
extension UIViewController {
func showAlert(_ title: String = "Alert", message: String) {
let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler:
nil))
present(alert, animated: true, completion: nil)
}
}
you can call this method from UIViewController like
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
showAlert(message: "This is alert message")
}

Answer 2

Reminder: Your model shouldn't know about any UI related stuffs. Instead you should create an extension to UIViewController, or create free function
As a free function
func showAlertViewOnto(controller: UIViewController, detailInfo: (title: String?, message: String?), handler: ((UIAlertAction) -> Void)? = nil ) {
let alert = UIAlertController(title:detailInfo.title , message: detailInfo.message, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler:
handler))
controller.present(alert, animated: true, completion: nil)
}
As an extension to your UIViewController
extension UIViewController {
func showAlertView(detailInfo: (title: String?, message: String?), handler: ((UIAlertAction) -> Void)? = nil ) {
let alert = UIAlertController(title:detailInfo.title , message: detailInfo.message, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler:
handler))
self.present(alert, animated: true, completion: nil)
}
}
To Use it
showAlertViewOnto(controller: self, detailInfo: (title: "Hello ", message: "welcome to our service"), handler: { _ in
// here you can add code once ok is pressed
})

Answer 3

There is a logical error in your code. An instance of LoginViewController is already present (in the navigation stack or is the initial view controller) which appears on the screen.
You created a new instance of LoginViewController in your model class
let controller = LoginViewController()
which is not added to your navigation stack, so you don’t see it on the screen.
controller.present(alert, animated: true, completion: nil)
Presenting UIAlertController over the new instance will not show user an alert since the controller here itself is not present on the screen.
You will need to present UIAlertController from the instance visible on screen(the initial one). You could change the functionshow_alert to the following:
class LoginModel{
func showAlert(forController controller: UIViewController /*you could add title, message and other stuff here if needed.*/){
let alert = UIAlertController(title: "Title", message: "Some Message",
preferredStyle: UIAlertControllerStyle.alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler:
nil))
controller.present(alert, animated: true, completion: nil)
}
And modify your call as follows:
LoginModel().showAlert(forController: self)