+ (void)choseRootVC{    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];    NSString *saveVersion = [defaults objectForKey:@"CFBundleVersion"];    NSString *currentVersion = [NSBundle mainBundle].infoDictionary[@"CFBundleVersion"];    if ([saveVersion isEqualToString:currentVersion]) {//两个版本号相同，不是第一次使用这个软件        IWTabBarController *main = [[IWTabBarController alloc]init];        [UIApplication sharedApplication].keyWindow.rootViewController = main;    }else//版本号不同，第一次使用这个软件    {        IWNewfeatureViewController *newfeature = [[IWNewfeatureViewController alloc]init];        [UIApplication sharedApplication].keyWindow.rootViewController = newfeature;    }}