title: Android Studio 3 - Constraint layout editor is not working
body: <p>I recently installed android studio 3 but The constraint layout shows a grey window..I tried everything but I couldn't fix the the problem</p>
  
  <p>Thanks in advance for any help provided:</p>
  
  <p><img src="https://i.stack.imgur.com/ioiHO.png" alt="enter image description here"></p>
  
  <p><img src="https://i.stack.imgur.com/vBg4y.png" alt="enter image description here"></p>
  
  <p>XML code:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt; 
  &lt;android.support.constraint.ConstraintLayout 
      xmlns:android="schemas.android.com/apk/res/android"; 
      xmlns:app="schemas.android.com/apk/res-auto"; 
      xmlns:tools="schemas.android.com/tools"; 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      tools:context="com.example.chihaoui.myapplication.MainActivi‌​ty"&gt; 
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>