title: creating a icon button that has a selector xml file as background
body: <p>I am trying to make a icon button that when the user clicks on it, as a click effect, the color of the icon changes. for this, i tried a selector xml file that select different png files, this is a simple selector code that I thaught it would work, but there must be something that I am missing, the xml file looks like this:</p>
  
  <pre><code>    &lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;selector xmlns:android="http://schemas.android.com/apk/res/android"&gt;
      &lt;item android:state_pressed="true"
          android:drawable="@drawable/continue_pressed"/&gt;
      &lt;item android:state_pressed="false"
          android:drawable="@drawable/continue_not_pressed"/&gt;
  &lt;/selector&gt;
  </code></pre>
  
  <p>however when I try to run the app on emulator, it crashes! and there is nothing in log so i can tell what the problem is. but when i try just one png file for the background of the button it works!
  the xml code for the button looks like this:</p>
  
  <pre><code>&lt;Button
              android:id="@+id/about_icon1"
              android:background="@drawable/button_continue"
              android:layout_width="100dp"
              android:layout_height="100dp"
              android:alpha="0.5" /&gt;
  </code></pre>
  
  <p>How can I fix this?</p>