title: Custom Preference with a StringSet
body: <p>I have a list of folders I'd like to display in a preference as a list of strings.  I'm storing the folders via <code>SharedPreferences.Editor.putStringSet()</code>. The user can click a row to remove that entry. </p>
  
  <p>I'm not sure how to display the values in a custom <code>Preference</code>; a ListView would be ideal.  The built in preferences don't support this use case and <code>Preference.getPersistedStringSet</code> is hidden "pending API approval", apparently for years, so a custom Preference won't work easily.</p>
  
  <p>I could use a delimited string with a static helper method within the custom <code>Preference</code> to ensure a call to <code>SharedPreferences.Editor.putString()</code> (instead of <code>putStringSet</code>) is formatted properly, but that's a bit sloppy.  Any better ideas?</p>