How to check text field input at real time?

Question

I am writing validation for my textfield, I found something interesting that whether I can check how many digits I am typing into the textfield at real time. My text field i

Answer 1

Set up a delegate for the UITextField and implement the method – textField:shouldChangeCharactersInRange:replacementString: Details and examples are in the UITextFieldDelegate Protocol Reference, but here's a quick example:

- (BOOL)textField:(UITextField *)textField 
shouldChangeCharactersInRange:(NSRange)range 
replacementString:(NSString *)string
{
        NSString *text = [textField text];
        // NOT BACKSPACE
        if ([string length] || text.length + string.length < 8) {
            return YES;
        } else if (text.length + string.length > 8) {
            return NO;
        } else {
                // DO SOMETHING FOR LENGTH == 8
                return YES;
        }
}