title: FragmentActivity: Cannot cast from Fragment to derived class
body: <p>I am trying to use a Fragment in a FragmentActivity like so:</p>
  
  <pre><code>TutViewerFragment viewer = (TutViewerFragment)    
  getSupportFragmentManager().findFragmentById(R.id.tutview_fragment);
  </code></pre>
  
  <p>And my <code>TutViewerFragment</code> extends <code>Fragment</code>. However I am getting an error:</p>
  
  <blockquote>
    <p>Cannot cast from Fragment to TutViewerFragment.  </p>
  </blockquote>
  
  <p>I really don't understand why this is happening.  Why can't it be cast?</p>