title: Android: Looping through pictures and setting each as background
body: <p>I have about 25 pictures in my <code>res/drawables</code>.
  I want to loop through them, setting the next one as the background everytime the user hits a button on the screen. </p>
  
  <p>Of course the drawables folder also has other pictures like droid icon etc which I don't want to use.</p>
  
  <p>Cannot think of a good way of doing it. I thought of naming my pictures back1.jpg, back2.jpg... back25.jpg, and somehow looping through but this doesn't work. Can someone suggest a way/ sample code? </p>