title: How to pop back to specify viewController from navigationController(viewControllers/stack)?
body: <p>I've created an application with serial views (A,B,C,D,...), and I need to pop back D to B.
  Someone may say Why not using:</p>
  
  <pre><code>[self.navigationController popToViewController:[[self.navigationController viewControllers] objectAtIndex:1] animated:YES];
  </code></pre>
  
  <p>However, it is not a good solution. Because this method needs you to get the index which our "B" is store in. </p>
  
  <p><strong>Question</strong>: How to get the index of "B" in the viewControllers?</p>
  
  <p>format in the <code>UIViewControllers</code> should be:<br>
      "&lt; A: 0x6e70710 >",
      "&lt; C: 0x6e30370 >",
      "&lt; B: 0x6988a70 >",
      "&lt; D: 0x6ea8950 >",
      "&lt; E: 0x6eaaad0 >"</p>
  
  <p>I've tried and failed to use <code>rangeOfString</code> and <code>hasPrefix</code> to get the "B" view's index.</p>