title: Android Using layer-list for button selector
body: <p>How do we use a layer-list as a drawable for a button.
  I have a button:
      </p>
  
  <pre><code>&lt;item android:state_pressed="true"&gt;
      &lt;shape&gt;
          &lt;gradient android:endColor="@color/white"
              android:startColor="@color/grey_blue_light" android:angle="90" /&gt;
          &lt;stroke android:width="1dp" android:color="@color/aqua_blue" /&gt;
          &lt;corners android:radius="3dp" /&gt;
          &lt;padding android:left="10dp" android:top="10dp"
              android:right="10dp" android:bottom="10dp" /&gt;
      &lt;/shape&gt;
  &lt;/item&gt;
  
  
  &lt;item android:state_focused="true"&gt;
  
  &lt;/item&gt;
  &lt;item&gt;
  
  &lt;/item&gt;
  </code></pre>
  
  <p></p>
  
  <p>Now I need a layer-list to be used as a shape when say button state is pressed:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;layer-list xmlns:android="http://schemas.android.com/apk/res/android"&gt;
  &lt;item&gt;
      &lt;shape android:shape="oval"&gt;
          &lt;solid android:color="@color/aqua_blue" /&gt;
      &lt;/shape&gt;
  &lt;/item&gt;
  &lt;item android:top="1dp" android:left="1dp" android:right="1dp" android:bottom="1dp"&gt;
      &lt;shape android:shape="oval"&gt;
          &lt;solid android:color="@color/aqua_blue" /&gt;
      &lt;/shape&gt;
  &lt;/item&gt;
  </code></pre>
  
  <p></p>
  
  <p>How do we use this layer list in the button selector?</p>