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)


// 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: UITextField.textDidChangeNotification, 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).count ?? 0
            let textIsNotEmpty = textCount > 0
            
            // If the text contains non whitespace characters, enable the OK Button
            okAction.isEnabled = textIsNotEmpty
        
    })
}

@Shivdayallall
This happens when you have a function with wrong argument names.
Change the argument name from: .UITextFieldTextDidChange
To: UITextField.textDidChangeNotification

@IlijaMihajlovic thanks

Created service-class for such kind of alert presentation + added text field delegate to restrict non-digit user input:
https://gist.github.com/SergLam/652db7cec81e7e5a5c0fda070d300a12

This happens when you have a function with wrong argument names.
Change the argument name from: .UITextFieldTextDidChange
To: UITextField.textDidChangeNotification

I changed, but anyway I get Type of expression is ambiguous without more context"

I get error: Cannot infer contextual base in reference to member 'UITextField'

thank you.

really cool, thanks.
I would add
okAction.isEnabled = false
before add it to alertController since the TextField appears empty the first time.

I second this. The OK button will start out as enabled if this is not done. Minor line of code but pretty essential given the purpose of the whole procedure.

Pretty neat. I didn't want to create a new method in an already clustered viewcontroller.