NSString is integer?

Question

How to check if the content of a NSString is an integer value? Is there any readily available way?

There got to be some better way then doing something like this:

Answer 1

Building on an answer from @kevbo, this will check for integers >= 0:

if (fooString.length <= 0 || [fooString rangeOfCharacterFromSet:[[NSCharacterSet decimalDigitCharacterSet] invertedSet]].location != NSNotFound) {
    NSLog(@"This is not a positive integer");
}

A swift version of the above:

func getPositive(incoming: String) -> String {
    if (incoming.characters.count <= 0) || (incoming.rangeOfCharacterFromSet(NSCharacterSet.decimalDigitCharacterSet().invertedSet) != nil) {
        return "This is NOT a positive integer"
    }
    return "YES! +ve integer"
}