Extract xml from zip to nsdata (cocoa)

I have a zip file with a .xml in it. This xml has to be unzipped and saved into NSData. I already know ziparchive and zippack. And I also know that I can unzip the archive, save it and get the xml file. But because of many other stuff in the zip that I don't need thats not very good for my case I think. Can anyone help? At the momen开发者_如何学运维t I'm able to get the file from zip, but the conversion to NSData fails with "Document empty".