title: Design screen disappeared in Android studio 2.2
body: <p>Recently I was playing with <code>ConstraintLayout</code> introduced in Android Studio 2.2 preview.</p>
  
  <p><a href="https://i.stack.imgur.com/S9fSS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/S9fSS.png" alt="enter image description here"></a></p>
  
  <p>Screen was like above, but suddenly I have pressed few keys and that black screen disappears.</p>
  
  <p><a href="https://i.stack.imgur.com/15EIx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/15EIx.png" alt="enter image description here"></a></p>
  
  <p>Does anyone have any idea about how to get back the design screen?</p>