Infinite loop in alertViewShouldEnableFirstOtherButton iOS5 - ios5

Question

I'm trying to change the first letter of the user input to the uppercase in the method alertViewShouldEnableFirstOtherButton. Everything works as expected in the iOS 6 but in iOS 5 it seems I get the infinite loop(when I set the text field of the alert view programmatically it calls the method alertViewShouldEnableFirstOtherButton recursively )
Here it is the code:
- (BOOL)alertViewShouldEnableFirstOtherButton:(UIAlertView *)alertView{
NSString *inputText = [[alertView textFieldAtIndex:0] text];
if(inputText.length==0)return NO;
unichar firstChar=[[inputText capitalizedString] characterAtIndex:0];
NSString *capitalizedLetter= [NSString stringWithCharacters:&firstChar length:1];
NSString *str=[inputText stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:capitalizedLetter];
[[alertView textFieldAtIndex:0] setText:str];// setText calls again alertViewShouldEnableFirstOtherButton
return YES;
}

Answer 1

- (BOOL)alertViewShouldEnableFirstOtherButton: is for the alertView to ask its delegate whether the first (non-cancel) button should be enabled or not.
The alertView is free to call this method at any time (for instance it might call it when its textfields are changed), to get a YES/NO answer from the delegate. Therefore, you should not implement side effects here.
I would recommend using something like [alertView textFieldAtIndex:0].delegate = self and use one of the textField delegate methods (for instance – textFieldDidBeginEditing:) to modify the string.

Answer 2

Actually I used the shouldChangeCharactersInRange method of UITextField to capitalize the first letter of the inserted string.
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
NSLog(#"range: %# string: %#", NSStringFromRange(range), string);
if ([string isEqualToString:#""]) {// detect when the user removes symbol
if ([textField.text length] > 0)textField.text = [textField.text substringToIndex:[textField.text length] - 1];//remove last character from the textfield
}
if (range.location==0) {//capitalize first letter
NSString *upperString = [[textField.text stringByAppendingString:string] uppercaseString];
textField.text = upperString;
}else {
textField.text=[textField.text stringByAppendingString:string];
}
return NO;
}