title: Count items in drawable folder that start with specific string
body: <p>How would I count the number of items in the drawable folder that start with "fr"?</p>
  
  <p>Background; I want to create a randomizer to pick a random image from the drawables folder. To make it future-proof, I want to set the max value of the randomizer to the number of items that are eligable for picking..</p>