UITextField delegate method shouldChangeCharactersInRange for allowing a valid currency value with the format of $x.xx. The following rules are enforced: 1) The value within the textField begins with a $ 2) Allows a decimal to be inserted only when there is 1 or more integers already in the field 3) Prevents more than 1 decimal to be inserted 4)…

CurrencyExample.mm

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

    NSString *textValue = textField.text;
    if(textValue.length > 0 && string.length > 0) {

        NSRange dotRange = [textValue rangeOfString:@"."];
        BOOL isDot = [string isEqualToString:@"."];

        if(isDot) {
            return (dotRange.length == 0);
        } else if(dotRange.length > 0) {
            return (int) textValue.length - dotRange.location - 1 < 2;
        }

        return YES;

    } else if(string.length == 0 && textValue.length > 1) {
        return YES;
    } else {
        textField.text = @"$";
    }

    return NO;
}