download a complete folder

in my app I use several png-graphics. For the present version they are installed with the app in the folder "graphic". I made while programming. Now I need some more png-graphics and I don't want to make each time an app-update. How can I manage it, that the app is downloading the png-files from my webserver without knowing the name. I am looking for something which compares the files on the webse开发者_高级运维rver with the files on the iPhone and if there is a new (or newer) file download it. Or is it possible to make an plist-file with the graphics??

If you enabled directory listing, you could parse the listing and download all files in there.