title: "Back" button doesn't show up in UINavigationController
body: <p>I'm using the following code to try to make a "back" button for my app, the view that this code is located is in a modal view (if that has any bearing?):</p>
  
  <pre><code>navBar = [[UINavigationController alloc] initWithRootViewController:tvController];
  
  [navBar.view setFrame:CGRectMake(0, 0, 320, 460)];
  self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle: @"Back"
                                                                             style: self.navigationController.navigationItem.leftBarButtonItem.style
                                                                            target: self
                                                                            action: @selector(backAction)];
  navBar.navigationItem.backBarButtonItem.enabled = YES;
  
  [self.view addSubview:navBar.view];
  </code></pre>
  
  <p>The view does not show at all, thank you for any tips!</p>
  
  <p>EDIT: Even if I use a leftBarButtonItem, it still does not show up, I think there is some problem with the self.navigationItem bit of my code?</p>