title: Android fragment transition callbacks
body: <p>is there a way to detect that a fragment has started transition (in or out). What I am trying to acheve:</p>
  
  <p>I have a fragment whcih has a SurfaceView with complex graphics in it. When I click on a button I want this fragment to slide away from the screen. But we all know, that SurfaceView can't be animated. So I want to replace it with a drawing cache bitmap before I start the transition.</p>
  
  <p>There fore I need to know when the fragment starts transition. This is especially important for open transitions, because I call replace with image routine manually before out transition, but I need to know when the open transition was complete. Is there a better way than a timer (which seems awful to me).</p>
  
  <p>Thanks.</p>
  
  <p>P. S. compatibility lib</p>