title: Getting all .pdf files from External storage on android
body: <p>I'm trying to get all pdf's recursively from the External storage. What I'd like to have, is an interface just like pdf reader's, meaning, that it loads the files asynchronously and displays each directory name in a separator. I've got the separator part down, but now I need the loading.</p>
  
  <p>Any tips on doing this? I know that I should just iterate through all files, check if the files is a directory and launch the recursive algorithm again, but how to write this to only show .pdf files?</p>