判断字符串是否只含有数字 - iOS

- (BOOL)validateNumber:(NSString*)number {
BOOL res = YES;
NSCharacterSet* tmpSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];
int i = 0;
while (i < number.length) {
    NSString * string = [number substringWithRange:NSMakeRange(i, 1)];
    NSRange range = [string rangeOfCharacterFromSet:tmpSet];
    if (range.length == 0) {
        res = NO;
        break;
    }
    i++;
}
return res;
}