title: Android change widget drawable opacity
body: <p>I want to change the widget background opacity, which is defined by a drawable including a color code, programmatically in the onEnabled method.</p>
  
  <p>This is the drawable:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;shape xmlns:android="http://schemas.android.com/apk/res/android"&gt;
      &lt;corners android:radius="5dp"/&gt;
      &lt;solid android:color="#FFFFFF"/&gt;
  &lt;/shape&gt;
  </code></pre>
  
  <p>I want to change the color opacity programmatically, how can I do that? I already tried using:</p>
  
  <pre><code>Drawable drawable = getResources().getDrawable(R.drawable.widget_shape);
  drawable.setAlpha(80);
  </code></pre>
  
  <p>But without success</p>