关于添加UINavigationController

如果给UIViewController添加作为modal的UINavigationController。

有一个flow,在firstViewController中开始，然后在view中调用secondViewController。

- (IBAction)PressButton:(id)sender {

    SecondViewController *second = [[SecondViewController alloc] init];
    second.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
    UINavigationController *nav = self.navigationController;
    [nav presentViewController:second animated:YES completion:nil];                              
}

在secondViewController 中希望能推进thirdViewController，但是没有用，我用了下面的方法尝试：

- (IBAction)pressButton:(id)sender {

   ThirdViewController *tvc = [[ThirdViewController alloc] init];
   UINavigationController *nav = self.navigationController;
   [nav pushViewController:tvc animated:YES];
}

点击 secondViewController 时完全没有反应。

请高手指点一下哪里出错了，谢谢
我用的：
OSX 10.8.2
Xcode 4.6
iOS 6.1

将第二个view作为导航控制器的root,同时从所属的view中调用当前ViewController

- (IBAction)PressButton:(id)sender {
        SecondViewController *second = [[SecondViewController alloc] init];
        second.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
        UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:second];
        [self presentViewController:navigationController animated:YES completion:nil];    
    }