Why can't I seem to unarchive objects in an iPhone app that were archived by an OS X app?

Question

I'm writing an iPhone app that is mainly centered around grid patterns, so I have a Pattern class which contains an NSMutableArray of NSMutableArrays. This class implements NSCoding, and it seems the following code works just fine in my iPhone app:

GridPattern * pattern = [GridPattern patternWithWidth:8 height:8];
[pattern setValueAtColumn:0 row:7 value:1];
[NSKeyedArchiver archiveRootObject:pattern toFile:@"test.pat"];
pattern = [NSKeyedUnarchiver unarchiveObjectWithFile:@"test.pat"];

If I debug the code above, I find after stepping over line 4, that I have a GridPattern object with the appropriate value set for column 0, row 7.

I have also written a Cocoa OSX application intended for creating patterns for the iPhone app, which also uses the same GridPattern class. It can also load and save the patterns successfully.

What I wanted to do was:

• create and save the patterns in the OS X app
• add the pattern files into Resources group in XCode for the iPhone app; (I added it as test.pat)

• unarchive the patterns in my iPhone app, using code such as:

  pattern = [NSKeyedUnarchiver unarchiveObjectWithFile:@"test.pat"];

However, when I try to unarchive the objects from this file, all that is returned is nil. I thought I might have had the file path wrong and also tried @"Resources/test.pat" to no avail.

Am I simply referring to the file incorrectly? Or are archived objects simply not cross-platform? Is this whole approach just plain wrong? If so, how would you do it?

Answer 1

I don't know about the compatibility of archiving across platforms, but to refer to a bundle resource, you should always use NSBundle to find it. Don't depend on the current path.

Answer 2

As your model is just an array of arrays, you could use XML property lists which do work across architectures.