How to limit character input in UIAlertView UITextField

Question

I am trying to limit the number of characters my user is allowed to input into my UITextField within my UIAlertView.

I've tried the some common answers on the web. Such as shown below :

  #define MAXLENGTH 10


- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    if ([textField.text length] > MAXLENGTH) {
        textField.text = [textField.text substringToIndex:MAXLENGTH-1];
        return NO;
    }
    return YES;
}

Anyone able to help?

Answer 1

.h file

  @property (strong,nonatomic)  UITextField *alertText;

@interface LocationSearchViewController : UIViewController<UITextFieldDelegate>

.m file

- (IBAction)butPostalCode:(id)sender {

UIAlertView *alrt=[[UIAlertView alloc]initWithTitle:@"" message:@"" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK", nil];
alrt.alertViewStyle = UIAlertViewStylePlainTextInput;
[[alrt textFieldAtIndex:0] setPlaceholder:@"Enter postal Code"];
alertText = [alrt textFieldAtIndex:0];
alertText.keyboardType = UIKeyboardTypeNumberPad;
alertText.delegate=self;
alrt.tag=100;
[alrt show];
}



-(BOOL) textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
if(yourtextfieldname.text.length >= 10 && range.length == 0) {
    return NO;

}
return YES;
}

Swift

class LocationSearchViewController: UIViewController, UITextFieldDelegate {

 Var alertText:UITextField!
}

func butPostalCode(sender: AnyObject) {
var alrt: UIAlertView = UIAlertView(title: "", message: "", delegate: self, cancelButtonTitle: "Cancel", otherButtonTitles: "OK")
alrt.alertViewStyle = .PlainTextInput
alrt.textFieldAtIndex(0).placeholder = "Enter postal Code"
alertText = alrt.textFieldAtIndex(0)
alertText.keyboardType = .NumberPad
alertText.delegate = self
alrt.tag = 100
alrt.show()
}

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
if yourtextfieldname.text.length >= 10 && range.length == 0 {
    return false
}
return true
}

Answer 2

Unfortunately this isn't allowed. You aren't allowed to mess with a UIAlertViews hierarchy and so you can't go changing things on it like the UITextFields properties.

Please see this link

Specifically

The UIAlertView class is intended to be used as-is and does not support subclassing. The view hierarchy for this class is private and must not be modified

EDIT

Whilst you shouldn't be messing with the UIAlertView hierarchy itself like I have said above, you might actually be able to set the UITextFields delegate but first you need to retrieve it. First make sure you have set the UITextFieldDelegate in the header file (.h file).

Then after you have created your UIAlertView and set the alertViewStyle: property, so we have something like

// We create an instance of our UIAlertView
UIAlertView *myAlert = [[UIAlertView alloc] initWithTitle:@"My Alert"
                                                  message:nil
                                                 delegate:self
                                        cancelButtonTitle:@"Cancel"
                                        otherButtonTitles:@"OK", nil];

// We set the alertViewStyle to a plain text input, so 1 textfield
[myAlert setAlertViewStyle:UIAlertViewStylePlainTextInput];

// Then we retrieve that UITextField from the index 0 
UITextField *plainTextField = [myAlert textFieldAtIndex:0];
// Now that we have retrieved the text field we can set the delegate on it/
// Probably best to give it a tag as well so we can identify it later.
[plainTextField setDelegate:self]; 
[plainTextField setTag:1001];

Once we have set the delegate you should then enter your method as shouldChangeCharactersInRange: is a UITextFieldDelegate method.

-(BOOL) textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    // Make sure that it is our textField that we are working on otherwise forget the whole thing.
    if([textField tag] == 1001) {
        if([textField text].length >= 10 && range.length == 0) {
            return NO;
        }
    }
    return YES;
}

Warning

As the text field being retrieved from textFieldAtIndex: is part of the UIAlertViews hierarchy Apple may class this as altering the UIAlertView which isn't allowed (See first part of answer) and whatever you do don't use addSubview: when using UIAlertViews