title: Tab Bar Controller does not display XIB UIViewController when tab is clicked
body: <p>Here is the scenario</p>
  
  <p>Create new project Tabbed Application.  Add new controller, TestViewController with XIB file, in the XIB file just add one button with text "TestViewControllerButton".</p>
  
  <p>If I create a button in FirstViewController, and add an action to go to TestViewController, the button in XIB file is displaed.</p>
  
  <pre><code>TestViewController* vc = [[TestViewController alloc] init];
  [self presentViewController:vc animated:YES completion:nil];
  </code></pre>
  
  <p>The problem is when I add TestViewController to tab controller (index 2, start from 0), it does not show the XIB (I mean, the button does not displayed).</p>
  
  <p>Here are my steps.  I add UIViewController in Tab Controller, then change the class to TestViewController in Identity Inspector.  Then add Tab Bar Item to TestViewController and link it to Tab Bar Controller, so when the last tab is clicked, it linked to TestViewController.  But the problem is, the button in the XIB is not displayed (I add the button in TestViewController.xib).</p>
  
  <p>Yeah, off course I can add the button directly in Main.storyboard in my TestViewController, but the idea is I want to manage the UI in TestViewController XIB, and the main.storyboard just load the view in TestViewController image.</p>
  
  <p>Ok, I add some screenshot to make understand.  This screen runs well when I do programmatically, run in UIViewController (code above - self presentViewController:vc animated:YES completion:nil).</p>
  
  <p><img src="https://i.stack.imgur.com/3ngIA.png" alt="Run in UiViewController"></p>
  
  <p>When I run from Tab</p>
  
  <p><img src="https://i.stack.imgur.com/EoAG1.png" alt="enter image description here"></p>
  
  <p>The setting I think is already correct (since it runs well in UIViewController)</p>
  
  <p><img src="https://i.stack.imgur.com/XWh2w.png" alt="Main storyboard custom class controller"></p>
  
  <p>Already set file owner to the TestViewController</p>
  
  <p><img src="https://i.stack.imgur.com/tNtxW.png" alt="File Owner"></p>
  
  <p>Already bind the outlet</p>
  
  <p><img src="https://i.stack.imgur.com/asa8N.png" alt="Outlet"></p>
  
  <p>Thanks!</p>