title: ConstraintLayout - proportional width/height to self?
body: <p>I'm trying to figure out how to achieve the following behaviour using constraint layout:</p>
  
  <ol>
  <li>Place a view in the center of the ConstraintLayout parent</li>
  <li>Make the view width to be half of the parent's width</li>
  <li>Make the view height equals to its width</li>
  </ol>
  
  <p>(i.e - place a square in the center)</p>
  
  <p>I tried to use this combination:</p>
  
  <pre><code>  android:layout_width="0dp"
    android:layout_height="0dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintDimensionRatio="2:1"
  </code></pre>
  
  <p>But I'm not sure how to continue from here</p>