title: How to change app:elevation programmatically
body: <p>My app is work for API 19. So I can't use android:elevation. So I app:elevation in my layout.</p>
  
  <p><a href="https://stackoverflow.com/questions/33054316/android-xml-androidelevation-vs-appelevation">Android XML: android:elevation vs. app:elevation</a></p>
  
  <p>For exemple :</p>
  
  <pre><code>&lt;android.support.design.widget.AppBarLayout
      android:id="@+id/appBar"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:theme="@style/AppTheme.AppBarOverlay"
      app:elevation="5dp"&gt;
  </code></pre>
  
  <p>How to change app:elevation programmatically ? I can change android:elevation but I can't find how to change app:elevation !</p>