i wonder if there's the possibility to get all filenames in a directory. I didn't found anything about that in the docs and would be happy if someone could point me in the right direction.
you need to get the File object for the directory first (using getFile()) then you'd call getDirectoryListing():
var dfo = Titanium.Filesystem.getFile(yourDir);
var fid = dfo.getDirectoryListing();