title: Can't add any items to activity_main.xml in Android Studio
body: <p>In Android Studio, I can't add any items from Palette to activity_main.xml in Design view. It just won't let me drag and drop them. Any idea why this happens?</p>
  
  <p>Here is the PrintScreen:</p>
  
  <p><img src="https://i.stack.imgur.com/Uphws.png" alt=""></p>