Wsrtjtyk

I am adding a UITextField to a UIAlertController, which appears as an AlertView. Before dismissing the UIAlertController, I want to validate the input of the UITextField. Based on the validation I want to dismiss the UIAlertController or not. But I have no clue how to prevent the dismissing action of the UIAlertController when a button is pressed. Has anyone solved this problem or any ideas where to start ? I went to google but no luck :/ Thanks!

You're correct: if the user can tap a button in your alert, the alert will be dismissed. So you want to prevent the user from tapping the button! It's all just a matter of disabling your UIAlertAction buttons. If an alert action is disabled, the user can't tap it to dismiss.

To combine this with text field validation, use a text field delegate method or action method (configured in the text field's configuration handler when you create it) to enable/disable the UIAlertActions appropriately depending on what text has (or hasn't) been entered.

Here's an example. We created the text field like this:

alert.addTextFieldWithConfigurationHandler {

    (tf:UITextField!) in

    tf.addTarget(self, action: "textChanged:", forControlEvents: .EditingChanged)

}

We have a Cancel action and an OK action, and we brought the OK action into the world disabled:

(alert.actions[1] as UIAlertAction).enabled = false

Subsequently, the user can't tap OK unless there is some actual text in the text field:

func textChanged(sender:AnyObject) {

    let tf = sender as UITextField

    var resp : UIResponder = tf

    while !(resp is UIAlertController) { resp = resp.nextResponder() }

    let alert = resp as UIAlertController

    (alert.actions[1] as UIAlertAction).enabled = (tf.text != "")

}

EDIT Here's the current (Swift 3.0.1 and later) version of the above code:

alert.addTextField { tf in

    tf.addTarget(self, action: #selector(self.textChanged), for: .editingChanged)

}

and

alert.actions[1].isEnabled = false

and

@objc func textChanged(_ sender: Any) {

    let tf = sender as! UITextField

    var resp : UIResponder! = tf

    while !(resp is UIAlertController) { resp = resp.next }

    let alert = resp as! UIAlertController

    alert.actions[1].isEnabled = (tf.text != "")

}

I've simplified matt's answer without the view hierarcy traversing. This is holding the action itself as a weak variable instead. This is a fully working example:

weak var actionToEnable : UIAlertAction?



func showAlert()

{

    let titleStr = "title"

    let messageStr = "message"



    let alert = UIAlertController(title: titleStr, message: messageStr, preferredStyle: UIAlertControllerStyle.Alert)



    let placeholderStr =  "placeholder"



    alert.addTextFieldWithConfigurationHandler({(textField: UITextField) in

        textField.placeholder = placeholderStr

        textField.addTarget(self, action: "textChanged:", forControlEvents: .EditingChanged)

    })



    let cancel = UIAlertAction(title: "Cancel", style: UIAlertActionStyle.Cancel, handler: { (_) -> Void in



    })



    let action = UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: { (_) -> Void in

        let textfield = alert.textFields!.first!



        //Do what you want with the textfield!

    })



    alert.addAction(cancel)

    alert.addAction(action)



    self.actionToEnable = action

    action.enabled = false

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

}



func textChanged(sender:UITextField) {

    self.actionToEnable?.enabled = (sender.text! == "Validation")

}

Cribbing off of @Matt's answer, here's how I did the same thing in Obj-C

- (BOOL)textField: (UITextField*) textField shouldChangeCharactersInRange: (NSRange) range replacementString: (NSString*)string

{

    NSString *newString = [textField.text stringByReplacingCharactersInRange: range withString: string];



    // check string length

    NSInteger newLength = [newString length];

    BOOL okToChange = (newLength <= 16);    // don't allow names longer than this



    if (okToChange)

    {

        // Find our Ok button

        UIResponder *responder = textField;

        Class uiacClass = [UIAlertController class];

        while (![responder isKindOfClass: uiacClass])

        {

            responder = [responder nextResponder];

        }

        UIAlertController *alert = (UIAlertController*) responder;

        UIAlertAction *okAction  = [alert.actions objectAtIndex: 0];



        // Dis/enable Ok button based on same-name

        BOOL duplicateName = NO;

        // <check for duplicates, here>



        okAction.enabled = !duplicateName;

    }





    return (okToChange);

}

I realise that this is in Objectiv-C but it shows the principal. I will update this with a swift version later.

You could also do the same using a block as the target.

Add a property to your ViewController so that the block (closure for swift) has a strong reference

@property (strong, nonatomic) id textValidationBlock;

Then create the AlertViewController like so:

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Title" message:@"Message" preferredStyle:UIAlertControllerStyleAlert];

UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {



}];



   __weak typeof(self) weakSelf = self;

UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"Ok" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

        [weakSelf doSomething];



}];

[alertController addAction:cancelAction];

[alertController addAction:okAction];

[alertController.actions lastObject].enabled = NO;

self.textValidationBlock = [^{

    UITextField *textField = [alertController.textFields firstObject];

    if (something) {

        alertController.message = @"Warning message";

        [alertController.actions lastObject].enabled = NO;

    } else if (somethingElse) {

        alertController.message = @"Another warning message";

        [alertController.actions lastObject].enabled = NO;

    } else {

        //Validation passed

        alertController.message = @"";

        [alertController.actions lastObject].enabled = YES;

    }



} copy];

[alertController addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {

    textField.placeholder = @"placeholder here";

    [textField addTarget:weakSelf.textValidationBlock action:@selector(invoke) forControlEvents:UIControlEventEditingChanged];

}];

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