View-based NSOutlineView Lion Backwards Compatibility?

Question

Can someone explain this crash I'm getting when attempting to use a view-based NSOutlineView? The crash only happens on OS X Lion (10.7), not Mountain Lion (10.8). If I run the app on ML, everything works fine. But if I run it on Lion, it crashes with the "cannot decode object of class (NSSourceListBackgroundView)" error below. This happens even if I set the build target (not just the deployment target) to the 10.7 SDK (it builds against both the 10.7 and 10.8 SDKs with no warnings or errors, and runs fine on 10.8 when built against either).

Am I unknowingly using some 10.8-only feature here that isn't being flagged by the compiler? I have customized the backgrounds of the NSTableCellView and NSTableRowView objects used by the outline view, if that matters, and my app uses Autolayout. I couldn't find anything in the Apple changelogs, header files, or NSOutlineView/NSTableView documentation about this, and I was under the impression that view-based NSOutlineViews were compatible with 10.7. I've used NSTableView extensively before, and never had problems like this, although this is the first time I've tried doing an NSOutlineView.

I searched for this on Google and quite a few other places, and all I was able to find was some discussion of what looks like an identical problem on a German-language site that didn't seem to have a resolution (from what I could tell using Google Translate).

*** -[NSKeyedUnarchiver decodeObjectForKey:]: cannot decode object of class (NSSourceListBackgroundView)
    0   CoreFoundation                      0x00007fff944fcf56 __exceptionPreprocess + 198
1   libobjc.A.dylib                     0x00007fff95110d5e objc_exception_throw + 43
2   CoreFoundation                      0x00007fff944fcd8a +[NSException raise:format:arguments:] + 106
3   CoreFoundation                      0x00007fff944fcd14 +[NSException raise:format:] + 116
4   Foundation                          0x00007fff96f29705 _decodeObjectBinary + 2714
5   Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
6   Foundation                          0x00007fff96f0145c -[NSArray(NSArray) initWithCoder:] + 486
7   Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
8   Foundation                          0x00007fff96f28ab2 _decodeObject + 201
9   AppKit                              0x00007fff91e08832 -[NSView initWithCoder:] + 1051
10  AppKit                              0x00007fff91e2667f -[NSScrollView initWithCoder:] + 240
11  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
12  Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
13  Foundation                          0x00007fff96f0145c -[NSArray(NSArray) initWithCoder:] + 486
14  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
15  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
16  AppKit                              0x00007fff91e08832 -[NSView initWithCoder:] + 1051
17  AppKit                              0x00007fff91e083a1 -[NSCustomView initWithCoder:] + 652
18  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
19  Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
20  Foundation                          0x00007fff96f0145c -[NSArray(NSArray) initWithCoder:] + 486
21  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
22  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
23  AppKit                              0x00007fff91e08832 -[NSView initWithCoder:] + 1051
24  AppKit                              0x00007fff91e083a1 -[NSCustomView initWithCoder:] + 652
25  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
26  Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
27  Foundation                          0x00007fff96f0145c -[NSArray(NSArray) initWithCoder:] + 486
28  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
29  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
30  AppKit                              0x00007fff91e08832 -[NSView initWithCoder:] + 1051
31  AppKit                              0x00007fff91e083a1 -[NSCustomView initWithCoder:] + 652
32  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
33  Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
34  Foundation                          0x00007fff96f0145c -[NSArray(NSArray) initWithCoder:] + 486
35  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
36  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
37  AppKit                              0x00007fff91e08832 -[NSView initWithCoder:] + 1051
38  AppKit                              0x00007fff91e083a1 -[NSCustomView initWithCoder:] + 652
39  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
40  Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
41  Foundation                          0x00007fff96f0145c -[NSArray(NSArray) initWithCoder:] + 486
42  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
43  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
44  AppKit                              0x00007fff91e08832 -[NSView initWithCoder:] + 1051
45  AppKit                              0x00007fff91e279cf -[NSClipView initWithCoder:] + 56
46  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
47  Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
48  Foundation                          0x00007fff96f0145c -[NSArray(NSArray) initWithCoder:] + 486
49  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
50  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
51  AppKit                              0x00007fff91e08832 -[NSView initWithCoder:] + 1051
52  AppKit                              0x00007fff91e2667f -[NSScrollView initWithCoder:] + 240
53  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
54  Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
55  Foundation                          0x00007fff96f0145c -[NSArray(NSArray) initWithCoder:] + 486
56  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
57  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
58  AppKit                              0x00007fff91e08832 -[NSView initWithCoder:] + 1051
59  AppKit                              0x00007fff91e083a1 -[NSCustomView initWithCoder:] + 652
60  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
61  Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
62  Foundation                          0x00007fff96f0145c -[NSArray(NSArray) initWithCoder:] + 486
63  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
64  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
65  AppKit                              0x00007fff91e08832 -[NSView initWithCoder:] + 1051
66  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
67  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
68  AppKit                              0x00007fff91ef993e -[NSWindowTemplate initWithCoder:] + 3998
69  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
70  Foundation                          0x00007fff96f2a976 -[NSKeyedUnarchiver _decodeArrayOfObjectsForKey:] + 1193
71  Foundation                          0x00007fff96f2a377 -[NSSet(NSSet) initWithCoder:] + 519
72  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
73  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
74  AppKit                              0x00007fff91d0d1b9 -[NSIBObjectData initWithCoder:] + 2099
75  Foundation                          0x00007fff96f29797 _decodeObjectBinary + 2860
76  Foundation                          0x00007fff96f28ab2 _decodeObject + 201
77  AppKit                              0x00007fff91d0c864 loadNib + 235
78  AppKit                              0x00007fff91d0bdb8 +[NSBundle(NSNibLoading) _loadNibFile:nameTable:withZone:ownerBundle:] + 217
79  AppKit                              0x00007fff91d0bcd3 +[NSBundle(NSNibLoading) loadNibFile:externalNameTable:withZone:] + 141
80  AppKit                              0x00007fff91d0bc16 +[NSBundle(NSNibLoading) loadNibNamed:owner:] + 364
81  AppKit                              0x00007fff91f7ccd7 NSApplicationMain + 398

Additional Info: Since NSSourceListBackgroundView is apparently not part of the public API, I started looking around for where it's being instantiated. From looking at the XML in my .xib file, I was able to determine that they are apparently subviews of the NSScrollView that contains the NSOutlineView in question (so IB puts them in there, apparently?). I inserted a log statement to dump the subviews of the NSScrollView and there are a bunch of NSSourceListBackgroundView objects in there.

There are two NSScroller objects and one NSClipView, as expected. But there are also a bunch of these NSSourceListBackgroundView objects that apparently can't be instantiated on Lion (and that have no corresponding public header file that I can see). None of my other view-based NSTableView objects have this, except for the NSOutlineView.

Also, I DO NOT have the highlight style set to "source list": it is set to "None".

Does anyone know what the purpose of these objects is, or why IB added them to my XIB file? Is my XIB corrupt? I would REALLY rather not have to rebuild it, so I'm hoping not.

Answer 1

I ended up fixing this by simply deleting the entire NSOutlineView and its containing NSScrollView from my xib file and reconstructing them exactly the same way from scratch. When I did this, the mysterious NSSourceListBackgroundView objects were no longer present in the xib, and the crash on Lion stopped happening. It seems to still work perfectly fine on both Lion and Mountain Lion without them.

I never found a great explanation for why they were ever there in the first place (and would be interested if anyone can reproduce it), but my guess is that this was caused by an Xcode/IB bug. I've noticed in the past that files created by IB can be a bit "brittle" and intolerant of lots of fiddling around with their options (which is sort of annoying since making it easy to change options is kind of the whole point of having IB instead of just doing everything in code). So probably I changed some option on that part of the UI that left these objects behind as "cruft" in the xib because IB didn't clean it up. Going straight to the final design when reconstructing it avoided the issue.