How do I validate TextFields in an UIAlertController?

Question

Can anyone tell me how to validate UITextFields inside of a UIAlertController?

I need it to prevent the user from clicking \"Save\" unless

Answer 1

This can be achieved via NSNotificationCenter before you display the alert controller, all you have to do is ask the notification center to observe the notification for UITextFieldTextDidChangeNotification and you should be good,

Given below is the implementation for the same

@IBAction func showAlert(sender: AnyObject) {

    var alert = UIAlertController(title: "New user",
        message: "Add a new user",
        preferredStyle: .Alert)

    let saveAction = UIAlertAction(title: "Save",
        style: .Default) { (action: UIAlertAction!) -> Void in

            println("do your stuff here")
    }

    saveAction.enabled = false

    let cancelAction = UIAlertAction(title: "Cancel",
        style: .Default) { (action: UIAlertAction!) -> Void in
    }


    alert.addTextFieldWithConfigurationHandler {
        (textFieldName: UITextField!) in
        textFieldName.placeholder = "Enter full name"
    }

    alert.addTextFieldWithConfigurationHandler {
        (textFieldEmail: UITextField!) in
        textFieldEmail.placeholder = "Enter valid email adress"
        textFieldEmail.keyboardType = .EmailAddress

    }
// adding the notification observer here
 NSNotificationCenter.defaultCenter().addObserverForName(UITextFieldTextDidChangeNotification, object:alert.textFields?[0],
        queue: NSOperationQueue.mainQueue()) { (notification) -> Void in

            let textFieldName = alert.textFields?[0] as! UITextField
            let textFieldEmail = alert.textFields![1] as! UITextField
            saveAction.enabled = self.isValidEmail(textFieldEmail.text) &&  !textFieldName.text.isEmpty
    }


    NSNotificationCenter.defaultCenter().addObserverForName(UITextFieldTextDidChangeNotification, object:alert.textFields?[1],
        queue: NSOperationQueue.mainQueue()) { (notification) -> Void in

            let textFieldEmail = alert.textFields?[1] as! UITextField
            let textFieldName = alert.textFields?[0] as! UITextField
            saveAction.enabled = self.isValidEmail(textFieldEmail.text) &&  !textFieldName.text.isEmpty
    }


    alert.addAction(saveAction)
    alert.addAction(cancelAction)

    presentViewController(alert,
        animated: true,
        completion: nil)

}

 //  email validation code method
func isValidEmail(testStr:String) -> Bool {
    let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}"
    if let emailTest = NSPredicate(format:"SELF MATCHES %@", emailRegEx) as NSPredicate? {
        return emailTest.evaluateWithObject(testStr)
    }
    return false
}