I have a TextField for IP Address. Currently I am validating my IP Address on click of a button like this:

```
- (IBAction)addPrinter:(id)sender {

     NSString* validIPRegEx = @"^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$";
     NSRegularExpression *regex = [NSRegularExpression
                                  regularExpressionWithPattern:validIPRegEx
                                  options:0
                                  error:nil];
     NSUInteger numberOfMatches = [regex numberOfMatchesInString:_printerIPAddress.text options:0 range:NSMakeRange(0, [_printerIPAddress.text length])];
    if (numberOfMatches!=1) {
        UIAlertView *myAlertView = [[UIAlertView alloc] initWithTitle:@"Error"
                                                              message:@"Invalid IP Address"
                                                             delegate:nil
                                                    cancelButtonTitle:@"OK"
                                                    otherButtonTitles: nil];
        [myAlertView show];
    }
}

```

But, my requirement is that I validate my IP Address on the go as user is entering text in TextField.

For example when user start typing in the TextField he should be allowed to enter a number between **0-255** before any of the three dot in an IP Address i.e if user has already typed 26 then the text shouldn't change if he types anything except a dot. Similarly the text should not change if he types any other character except numbers and dot.

I have searched a lot about this but found no help. Any help regarding this will be appreciated.

Thanks in advance!