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

func getPositive(input: String) -> String {
    if (input.count <= 0) || (input.rangeOfCharacter(from: NSCharacterSet.decimalDigits.inverted) != nil) {
        return "This is NOT a positive integer"
    }
    return "YES! integer"
}

Update @coco's answer for Swift 5