title: NAvigationController Bar Buttons not showing
body: <p>I have NavigationViewController class and in <code>viewDidload</code> methods 
  like this. but Bar Buttons not showing any clue?    </p>
  
  <pre><code>MapViewController *p=[[MapViewController alloc]initWithNibName:self.nibName bundle:[NSBundle mainBundle]];
      UIBarButtonItem *rightButton = [[UIBarButtonItem alloc]
                                      initWithTitle:@"Code"
                                      style:UIBarButtonItemStylePlain
                                      target:self
                                      action:@selector(showDocco:)];
      [[self navigationController] setNavigationBarHidden:NO animated:NO];
       self.navigationItem.rightBarButtonItem = rightButton;
  
      self.modalPresentationStyle=UIModalPresentationFormSheet;
      [self pushViewController:p animated:YES];
  </code></pre>