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

Register for the text field change notifications and validate the text fields there:

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

let textFieldValidationObserver: (NSNotification!) -> Void = { _ in
    let textFieldName = alert.textFields![0] as! UITextField
    let textFieldEmail = alert.textFields![1] as! UITextField
    saveAction.enabled = self.isValidEmail(textFieldEmail.text) && textFieldName.text.length > 0
}

// Notifications for textFieldName changes
NSNotificationCenter.defaultCenter().addObserverForName(UITextFieldTextDidChangeNotification,
    object: alert.textFields![0],  // textFieldName
    queue: NSOperationQueue.mainQueue(), usingBlock: textFieldValidationObserver)

// Notifications for textFieldEmail changes
NSNotificationCenter.defaultCenter().addObserverForName(UITextFieldTextDidChangeNotification,
    object: alert.textFields![1],  // textFieldEmail
    queue: NSOperationQueue.mainQueue(), usingBlock: textFieldValidationObserver)

alert.addAction(saveAction)
//...

Answer 2

Following what @Kupendiran presented for email input validation with UIAlertController. Here is a version thats working with Objective-C and the newer UIAlertController format as UIAlertView is now depreciated.

Step 1. add the following to .h and .m files with other properties and variables

.h

@property(strong,nonatomic)UITextField *emailAddressField;

.m

UITextField *emailAddressField;

Step 2. Create the alert message, buttons and validation process.

UIAlertController * alertView =   [UIAlertController
                                           alertControllerWithTitle:@"E-Mail Address"
                                           message:@"Enter your email address:"
                                           preferredStyle:UIAlertControllerStyleAlert];

        [alertView addTextFieldWithConfigurationHandler:^(UITextField *emailTextField) {
            emailTextField.placeholder = @"E-Mail Address";
            emailTextField.autocorrectionType= UITextAutocorrectionTypeYes;
            emailTextField.keyboardType= UIKeyboardTypeEmailAddress;

            emailAddressField = emailTextField;
        }];

Step 3. Create the alert actions

        UIAlertAction * ok= [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
            //Handel your OK button action here
            NSLog(@"Email Address Entered is: %@", emailAddressField.text);

            //Validate email address is correct format
            if(emailAddressField.text.length>0){//

                NSString *emailString= emailAddressField.text;
                NSString *emailReg= @"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}";
                NSPredicate *emailTest= [NSPredicate predicateWithFormat:@"SELF MATCHES %@",emailReg];

                if(([emailTest evaluateWithObject:emailString]!=YES) || [emailString isEqualToString:@""]){

                    NSLog(@"Email Address Entered is not valid: %@", emailAddressField.text);

                    UIAlertController *badEmailAlert = [UIAlertController
                                                     alertControllerWithTitle:@"Email Address"
                                                                      message:@"\nPlease enter valid Email (example@example.com format) ."
                                                               preferredStyle:UIAlertControllerStyleAlert];
                    [self presentViewController:badEmailAlert animated:YES completion:nil];

                    UIAlertAction* cancel = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleDefault
                                                                   handler:^(UIAlertAction * action) {
                                                                       [badEmailAlert dismissViewControllerAnimated:YES completion:nil];
                                                                       [self presentViewController:alertView animated:YES completion:nil];
                                                                   }];
                    [badEmailAlert addAction:cancel];


                }else{

                    NSLog(@"your TextField successfully validated");

                }
            }else{

                [self presentViewController:alertView animated:YES completion:nil];

            }

        }];
        [alertView addAction:ok];


        //Handel your Cancel button action here
        UIAlertAction* cancel = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleDefault
                                                       handler:^(UIAlertAction * action) {
                                                           [alertView dismissViewControllerAnimated:YES completion:nil];
                                                       }];
        [alertView addAction:cancel];

Step 4. Present the alert message on the screen

[self presentViewController:alertView animated:YES completion:nil];

Answer 3

This can be done by extending UIAlertViewController:

extension UIAlertController {

    func isValidEmail(_ email: String) -> Bool {
        return email.characters.count > 0 && NSPredicate(format: "self matches %@", "[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,64}").evaluate(with: email)
    }

    func isValidPassword(_ password: String) -> Bool {
        return password.characters.count > 4 && password.rangeOfCharacter(from: .whitespacesAndNewlines) == nil
    }

    func textDidChangeInLoginAlert() {
        if let email = textFields?[0].text,
            let password = textFields?[1].text,
            let action = actions.last {
            action.isEnabled = isValidEmail(email) && isValidPassword(password)
        }
    }
}

// ViewController
override func viewDidLoad() {
    super.viewDidLoad()

    let alert = UIAlertController(title: "Please Log In", message: nil, preferredStyle: .alert)

    alert.addTextField {
        $0.placeholder = "Email"
        $0.addTarget(alert, action: #selector(alert.textDidChangeInLoginAlert), for: .editingChanged)
    }

    alert.addTextField {
        $0.placeholder = "Password"
        $0.isSecureTextEntry = true
        $0.addTarget(alert, action: #selector(alert. textDidChangeInLoginAlert), for: .editingChanged)
    }

    alert.addAction(UIAlertAction(title: "Cancel", style: .cancel))

    let loginAction = UIAlertAction(title: "Submit", style: .default) { [unowned self] _ in
        guard let email = alert.textFields?[0].text,
            let password = alert.textFields?[1].text
            else { return } // Should never happen

        // Perform login action
    }

    loginAction.isEnabled = false
    alert.addAction(loginAction)
    present(alert, animated: true)
}

Answer 4

Most elegant way is to use

NotificationCenter.default.addObserver(forName: NSNotification.Name.UITextFieldTextDidChange...

Swift 3.0 example

let alert = UIAlertController(title: nil, message: nil, preferredStyle: .alert)
    alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
    let saveAction = UIAlertAction(title:"Save", style: .destructive, handler: { (action) -> Void in

    })
    alert.addAction(saveAction)
    alert.addTextField(configurationHandler: { (textField) in
        textField.placeholder = "Enter something"
        NotificationCenter.default.addObserver(forName: NSNotification.Name.UITextFieldTextDidChange, object: textField, queue: OperationQueue.main) { (notification) in
            saveAction.isEnabled = textField.text!.length > 0
        }
    })
    present(alert, animated: true, completion: nil)

Answer 5

For Swift 4.2 (NSNotification.Name.UITextFieldTextDidChange) update:

let alert = UIAlertController(title: nil, message: nil, preferredStyle: .alert)
    alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
    let saveAction = UIAlertAction(title:"Save", style: .destructive, handler: { (action) -> Void in

    })
    alert.addAction(saveAction)
    alert.addTextField(configurationHandler: { (textField) in
        textField.placeholder = "Enter something"
        NotificationCenter.default.addObserver(forName: UITextField.textDidChangeNotification, object: textField, queue: OperationQueue.main) { (notification) in
            saveAction.isEnabled = textField.text?.count > 0
        }
    })
    present(alert, animated: true, completion: nil)

Answer 6

Swift 4.0 Example

This is based on Mihael Isaev's answer. I had to change it up a bit to get the Save button to NOT be active immediately. I tried with and without the placeholder text. In the end, had to specifically inactivate Save to start with. In my case, I elected to use an alert title rather than placeholder text. But, it worked the same either way.

let alert = UIAlertController(title: "Enter Username", message: nil, preferredStyle: .alert)

alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: { (action) -> Void in}))
let saveAction = UIAlertAction(title:"Save", style: .destructive, handler: { (action) -> Void in
})
alert.addAction(saveAction)
alert.addTextField(configurationHandler: { (textField) in
    textField.text = ""
    saveAction.isEnabled = false
    NotificationCenter.default.addObserver(forName: NSNotification.Name.UITextFieldTextDidChange, object: textField, queue: OperationQueue.main) { (notification) in
        saveAction.isEnabled = textField.text!.length > 0
    }
})
self.present(alert, animated: true, completion: nil)