Write and Read to a iOS device! Help

Hi everyone! I've been working on a code for 1 1/2 day to use on iOS device. I've been using testing it on a mac, but switching it iOS didn't go well. I thought i could just switch from using Application.dataPath to peristentDataPath and it would work. But NO! I'm not familiar with using a serializer, so i followed this example http://unitynoobs.blogspot.no/2011/04/xml-writing-to-existing-xml-file.html. I used a StreamWriter and created a .txt file, is it a way to use these together. I would really be greatful for a simple but a full example how to get this done :) Thank you in advance.