title: List all of one file type on Android device?
body: <p>For example, I want to retrieve a list of all .mp3 files on the internal AND external storage. I would also like the path (<code>String</code>) of each .mp3 file for reference (store them in a <code>List</code>?) How could I do this? Is this a relatively expensive operation? If so, should it be put on a thread and while that is running, present the user with a "Loading" <code>ProgressDialog</code>?</p>