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I'd like to store some additional information along with a document, but I can't use bundles or packages, and I cannot store it inside the document itself.

The application is a text editor, and I'd like it to store code folding and bookmark locations with the document, but obviously this cannot be embedded into the code directly, and I don't want to alter the code with ugly comments.

Can I use NSDocument to store information in the resource fork of a document? If so, how can I do this? Should I directly write to <filename>/..namedfork/rsrc or is there an API available?

Peter Mortensen
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3 Answers3

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First, don't use the resource fork. It's virtually deprecated. Instead, use extended attributes. They can be set programmatically at the BSD level via setxattr and getxattr. Extended attributes are used in many places... for example, in the latest OS X, the resource fork itself is implemented as a special type of extended attributes.

For example, the Cocoa text system automatically adds an extended attribute to a file to specify the encoding.

I thought NSFileManager and NSFileWrapper supported extended attributes since Snow Leopard, but I can't find any documentation :p You can always use the BSD level functions, though.

Yuji
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Does the state need to move with the file if it's copied to another computer? If not, you could do a lot worse than emulating the way Bare Bones handles document state with BBEdit. They store state for all documents in ~/Library/Preferences/com.barebones.bbedit.PreferenceData/Document State.plist.

The resource fork documentation is here. But it contains plenty of suggestions to not use the resource fork.

SSteve
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I have a class on my web site for reading and writing resource forks, which I have never got around to moving to my GitHub repository because, as Yuji points out, they are not really used any more.

I was going to say alias files and web Internet location file are the only places they are used, but I used and tested it on Mac OS X v10.7 (Lion), and they are not even used there any more; they may still be used for custom icons. I didn't test for that exclusively. I will have to see how that affect my NDAlias class on 10.7.

ndresourcefork

Peter Mortensen
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Nathan Day
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  • Dear Nathan, nice to see you here! I used your `NDAlias` in my project which helped me greatly. (I moved to the official bookmark API in `NSURL`, though.) – Yuji Aug 09 '11 at 18:05
  • Yeah I have heard about that I will have to look into it. – Nathan Day Aug 12 '11 at 05:17