title: Switch between UITabBarController and UINavigationController
body: <p>The main functionality of my app is controlled by a UITabBarController.  However, I need to load a View that has a UINavigationController.  When I return to my UITabBarController using </p>
  
  <pre><code>        self.tabBarController.selectedViewController = [self.tabBarController.viewControllers objectAtIndex:0];
  </code></pre>
  
  <p>My UITabBarController no longer responds to clicks.  It seems like the View does not have focus.</p>
  
  <p>However, if I use this code to switch back to the UITabBarController:</p>
  
  <pre><code>[window addSubview:tabBarController.view]
  </code></pre>
  
  <p>My buttons will respond.  I feel like "addSubview" is less efficient because I never remove the view from the window and therefore it must be adding a second copy of the view to the stack.  Am I correct?  Is there a way to use the first method and make my buttons respond?  Please let me know.</p>