alert_controller_alert.swift

//create object
        let alertController = UIAlertController(title: "Login ✉︎", message: "Please enter your username/email and password.", preferredStyle: .alert)
        
        // create action object
        // which can be used to handle the different action when user tapped on any one of them
        let okAction = UIAlertAction(title: "Ok", style: .default) { (action) in
            //handle ok button action
            print("ok button tapped")
        }
        
        let cancelAction = UIAlertAction(title: "Cancel", style: .destructive) { (action) in
            //handle cancel button
            print("cancel button tapped")
        }
        
        //add two button action to the alert controller
        alertController.addAction(okAction)
        alertController.addAction(cancelAction)
        
        //adding user input to the alertcontroller
        alertController.addTextField { (textField) in
            textField.placeholder = "Enter username"
            textField.keyboardAppearance = .dark
            textField.keyboardType = .emailAddress
        }
        
        alertController.addTextField { (textField) in
            textField.placeholder = "Enter password"
            textField.keyboardAppearance = .dark
            textField.isSecureTextEntry = true
        }
        
        //display
        present(alertController, animated: true, completion: nil)