title: iOS - [ObjC] NavigationBarButtonItem is not showing when the navigation bar's root view is presented modally
body: <p>In my app I have two tabs that handle different set of functions.</p>
  
  <p>One tab is the user tab, when the user switch to this tab, the tab controller checks whether the user has logged in. If not, it shows a button(<code>LoginBtn</code>) which triggers a log in view controller to show when tapped.</p>
  
  <p>I intend to present the log in controller modally with a navigation bar.</p>
  
  <p>However, the navigation bar is not showing the right button item although I've initiated it.</p>
  
  <p>Here's the code</p>
  
  <pre><code>- (void)clickLoginBtn{
      LogginController* _cLogginController = [[LogginController alloc] init];
  
      UINavigationController *_cNavController = [[UINavigationController alloc] initWithRootViewController:_cLogginController];
  
      _cNavController.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"取消" style:UIBarButtonItemStylePlain target:self action:@selector(dismissLoginView)];
      [_cNavController.navigationItem.rightBarButtonItem setTintColor:kColorWhite];
      _cNavController.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
      [self presentViewController:_cNavController animated:YES completion:nil];
  }
  </code></pre>
  
  <p>What could be the problem? Is it possible that is because I present to controller modally?</p>