title: Change Button Shape on selected State?
body: <p>I have an Android Button: </p>
  
  <pre><code>&lt;Button
         android:layout_width="wrap_content"
         android:layout_height="44dp"
         android:background="@drawable/action_button" /&gt;
  </code></pre>
  
  <p><code>action_button.xml</code> is:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;shape xmlns:android="http://schemas.android.com/apk/res/android"
         android:shape="rectangle"&gt;
  
      &lt;padding
          android:left="25dp"
          android:right="25dp"/&gt;
  
      &lt;gradient
          android:angle="0"
          android:endColor="@color/whiteColor"
          android:startColor="@color/whiteColor"/&gt;
  
      &lt;corners android:radius="@dimen/borderRadius"/&gt;
  
      &lt;stroke
          android:width="2px"
          android:color="@color/actionColor"/&gt;
  &lt;/shape&gt;
  </code></pre>
  
  <p>How can I change the shape, when the button is pressed?</p>