Disable Alert Controller button if Alert Controller text field is empty or whitespace

Disable Alert Button.swift

import UIKit

// Create an alert controller
let alertController = UIAlertController(title: "Alert", message: "Please enter text", preferredStyle: .alert)

// Create an OK Button
let okAction = UIAlertAction(title: "OK", style: .default) { (_) in
    // Print "OK Tapped" to the screen when the user taps OK
    print("OK Tapped")
}

// Add the OK Button to the Alert Controller
alertController.addAction(okAction)
//Disble okAction as textField is empty at the first time
 okAction.isEnabled = false

// Add a text field to the alert controller
alertController.addTextField { (textField) in
    
    // Observe the UITextFieldTextDidChange notification to be notified in the below block when text is changed
    NotificationCenter.default.addObserver(forName: .UITextFieldTextDidChange, object: textField, queue: OperationQueue.main, using:
        {_ in
            // Being in this block means that something fired the UITextFieldTextDidChange notification.
            
            // Access the textField object from alertController.addTextField(configurationHandler:) above and get the character count of its non whitespace characters
            let textCount = textField.text?.trimmingCharacters(in: .whitespacesAndNewlines).characters.count ?? 0
            let textIsNotEmpty = textCount > 0
            
            // If the text contains non whitespace characters, enable the OK Button
            okAction.isEnabled = textIsNotEmpty
        
    })
}