Question

I have a question about text field. I am writing to let the user only can enter number into the text field.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    static NSCharacterSet *charSet = nil;
    if(!charSet) {
        charSet = [[[NSCharacterSet characterSetWithCharactersInString:@"0123456789"] invertedSet] retain];
    }
    NSRange location = [string rangeOfCharacterFromSet:charSet];
    return (location.location == NSNotFound);
}

Above is the code, it works fine now, the only thing is how can I release charSet since I retain it already. If I release it here, it will crash. Please text me the way. Or is it still ok if I keep it retain like that?

Answer 1

You should never have retained charSet in the first place. It is autoreleased when it comes to you: it lives long enough for the rest of your code to run, and then goes out of existence all by itself.

Of course if you use iOS 5 and ARC you’ll never have to worry about retain and release again…

EDIT: Oh, I see what the problem is, you’re assigning to a static. Okay then, just retain it as you are doing, and let it leak later on. Either that or use an instance variable and that way you can memory-manage it. Sorry about getting the answer wrong the first time, but better to admit that I read carelessly… 🙂

ANOTHER EDIT: But why are you assigning to a static? Do you really think this is saving you a lot of time? Isn’t this a case of “premature optimization”? Computers are really fast, much much faster than the user can type; I think your device can very happily calculate [[NSCharacterSet characterSetWithCharactersInString:@"0123456789"] invertedSet] every time through this routine without slowing things down.