title: Can't activate Preview mode Android Studio
body: <p>I am trying to switch over to the new Android Studio (awesome btw) but I can' activate the "Preview" window to view my XML files like they demo'd in I/O.</p>
  
  <p>When I navigate to View-->Tool Windows-->Preview   'Preview' is greyed out and I can't select it.</p>
  
  <p>Does anyone know a fix for this?</p>