What are good apps for file sharing online?

How & why do some apps only use iTunes File sharing in one direction?

• Some apps (e.g. Write for iPhone & Scanner Mini) allow you to copy files out of the app into the computer using iTunes, but will not recognize files you place in the app's 'folder'. I read on Apple developer that iTunes file sharing exposes the app's documents directory to the user. So my question is, how and why do the aforementioned apps (and others like them) avoid recognizing files added from the PC while allowing the user to copy files made in the app?

• Answer:

  I'm not sure what your question is. An app writes it's own objects and methods for selecting files to open- there is no pre-made open dialog box like in OSX and Windows. Some programs generate files from scratch and do not open and re-edit, so they would only write and not read. Others store proprietary files internally, such as in the Library folder, and only export files in more common formats to the Documents folder. It's all just software design decisions.