title: Animating fragments and the back stack
body: <p>I am having trouble using or understanding how popping 
  FragmentTransactions off of the back stack handles the custom 
  animations. Specifically, I expect it to call the "out" animation, but 
  it doesn't seem to. </p>
  
  <p>I have a simple method to handle a fragment transaction 
  (FragmentTransaction) where I add a fragment and apply a custom 
  transition so that it will fade-in/fade-out. I am also adding this to 
  the back stack so that the user can undo that transaction with the 
  back button, essentially navigating to the state before the fragment 
  was added. </p>
  
  <pre><code>protected void changeFragment() { 
      FragmentTransaction ft = fm.beginTransaction(); 
      ft.setCustomAnimations(android.R.anim.fade_in, android.R.anim.fade_out); 
      ft.add(R.id.fragment_container, new TestFragment()); 
      ft.addToBackStack(null); 
      ft.commit(); 
  } 
  </code></pre>
  
  <p>Everything works great moving forward, but when the user clicks the 
  back button, the transition animations do not reverse. What I expected 
  was that when the fragment got removed, it would use the fade out 
  animation. Instead it seems to pop out (without animation) and then 
  the container seems to fade in. I'm not sure that this is exactly what 
  is happening, but the fragment is definitely not fading out.  </p>
  
  <p>My application uses the compatibility library to add fragment support, 
  but I assume this to be applicable to Honeycomb (android-11) as well. 
  Does anyone know if I am just doing something wrong here or if I am 
  just expecting too much? Ideally, I would like to animate the 
  fragments similarly to how Gmail (on the Xoom) does in regards to 
  moving forward by clicking a message and then back by using the back 
  button. Preferably not having to override the back button 
  functionality and keep up with my own fragment state since I could 
  have several "transactions" that I would want to back out of and I am 
  not a fan of re-inventing wheels.</p>
  
  <p>Also asked on the Android Developers Group: <a href="http://groups.google.com/group/android-developers/browse_thread/thread/1136a3a70fa0b6e9">http://groups.google.com/group/android-developers/browse_thread/thread/1136a3a70fa0b6e9</a></p>