在这种情况下，pushViewController的正确方法是什么？

Question

我有一个自定义的UITabBarController。在它上面我添加了3个视图控制器，首先为每个控制器添加一个navigationController。看起来像这样

·customTabBarController.m viewDidLoad：

- (void)viewDidLoad
{
    [super viewDidLoad];

    FirstViewController *firstController = [[FirstViewController alloc] initWithNibName:@"FirstViewController" bundle:nil];
    UINavigationController *firstNavController = [[UINavigationController alloc] initWithRootViewController:firstController];

    SecondViewController *secondController = [[SecondViewController alloc] initWithNibName:@"SecondViewController" bundle:nil];
    UINavigationController *secondNavController = [[UINavigationController alloc] initWithRootViewController:secondController];

    self.viewControllers = [NSArray arrayWithObjects:firstNavController, secondNavController, nil];

    [self addLeftButtonImage];
    [self addRightButtonImage];
    self.selectedIndex = 1;
}

现在，当我在视图控制器上并且我想要pushViewController时，我该如何调用它？