Simple document app, throwing an exception on "revert to saved" in Mac OS X 10.7 Lion - objective-c

Question

I have a simple document app, based on the document template, which is throwing an exception when the "Revert to Saved -> Last Opened Version" menu item is selected on Mac OS X 10.7.
The exception isn't in my code, it's inside Cocoa. It also doesn't appear to be related to anything I'm doing. My app is very simple (at this stage), almost a vanilla cocoa document based app, based on the template included with the latest stable version of Xcode.
I realise this is probably a bug in Lion, but I need to find a workaround.
See below for the exception, and the entire contents (very small) of my NSDocument subclass.
Steps to reproduce
open any document
type a single character into the text view
select File -> Revert to Saved
click Last Opened Version
Exception
2011-09-04 07:10:29.182 myapp[15433:707] *** -[NSPathStore2 stringByAppendingPathExtension:]: nil argument
2011-09-04 07:10:29.191 myapp[15433:707] (
0 CoreFoundation 0x00007fff89c2b986 __exceptionPreprocess + 198
1 libobjc.A.dylib 0x00007fff90c6ed5e objc_exception_throw + 43
2 CoreFoundation 0x00007fff89c2b7ba +[NSException raise:format:arguments:] + 106
3 CoreFoundation 0x00007fff89c2b744 +[NSException raise:format:] + 116
4 Foundation 0x00007fff86d2b172 -[NSPathStore2 stringByAppendingPathExtension:] + 112
5 AppKit 0x00007fff9148f8c3 -[NSDocument _preserveCurrentVersionForReason:error:] + 579
6 AppKit 0x00007fff9147655b __-[NSDocument _revertToVersion:preservingFirst:error:]_block_invoke_3 + 99
7 Foundation 0x00007fff86ef28c3 __-[NSFileCoordinator coordinateReadingItemAtURL:options:error:byAccessor:]_block_invoke_1 + 113
8 Foundation 0x00007fff86ef2f34 -[NSFileCoordinator(NSPrivate) _invokeAccessor:orDont:thenRelinquishAccessClaimForID:] + 202
9 Foundation 0x00007fff86d98a28 -[NSFileCoordinator(NSPrivate) _coordinateReadingItemAtURL:options:error:byAccessor:] + 663
10 Foundation 0x00007fff86ef284c -[NSFileCoordinator coordinateReadingItemAtURL:options:error:byAccessor:] + 79
11 AppKit 0x00007fff91484b41 __-[NSDocument _revertToVersion:preservingFirst:error:]_block_invoke_1 + 347
12 AppKit 0x00007fff914901e3 -[NSDocument performSynchronousFileAccessUsingBlock:] + 42
13 AppKit 0x00007fff9148fc90 -[NSDocument _revertToVersion:preservingFirst:error:] + 125
14 AppKit 0x00007fff91476cf9 -[NSDocument _revertToDiscardRecentChangesPreservingFirst:error:] + 43
15 AppKit 0x00007fff91477094 __-[NSDocument _revertToDiscardRecentChangesThenContinue:]_block_invoke_3 + 164
16 AppKit 0x00007fff91474851 __-[NSDocument performSynchronousFileAccessUsingBlock:]_block_invoke_1 + 19
17 AppKit 0x00007fff91475bda -[NSDocument continueFileAccessUsingBlock:] + 227
18 AppKit 0x00007fff91490413 -[NSDocument _performFileAccessOnMainThread:usingBlock:] + 466
19 AppKit 0x00007fff9149023f -[NSDocument performSynchronousFileAccessUsingBlock:] + 134
20 AppKit 0x00007fff91495891 __-[NSDocument _revertToDiscardRecentChangesThenContinue:]_block_invoke_2 + 301
21 AppKit 0x00007fff914909a9 -[NSDocument _something:wasPresentedWithResult:soContinue:] + 21
22 AppKit 0x00007fff91381bee -[NSAlert didEndAlert:returnCode:contextInfo:] + 93
23 AppKit 0x00007fff9138e356 -[NSApplication endSheet:returnCode:] + 275
24 AppKit 0x00007fff91381ab4 -[NSAlert buttonPressed:] + 265
25 CoreFoundation 0x00007fff89c1b11d -[NSObject performSelector:withObject:] + 61
26 AppKit 0x00007fff911dd852 -[NSApplication sendAction:to:from:] + 139
27 AppKit 0x00007fff911dd784 -[NSControl sendAction:to:] + 88
28 AppKit 0x00007fff911dd6af -[NSCell _sendActionFrom:] + 137
29 AppKit 0x00007fff911dcb7a -[NSCell trackMouse:inRect:ofView:untilMouseUp:] + 2014
30 AppKit 0x00007fff9125c57c -[NSButtonCell trackMouse:inRect:ofView:untilMouseUp:] + 489
31 AppKit 0x00007fff911db786 -[NSControl mouseDown:] + 786
32 AppKit 0x00007fff911a666e -[NSWindow sendEvent:] + 6280
33 AppKit 0x00007fff9113ef19 -[NSApplication sendEvent:] + 5665
34 AppKit 0x00007fff910d542b -[NSApplication run] + 548
35 AppKit 0x00007fff9135352a NSApplicationMain + 867
36 myapp 0x00000001000018d2 main + 34
37 myapp 0x00000001000018a4 start + 52
)
NSDocument Subclass
#implementation MyTextDocument
#synthesize textStorage;
#synthesize textView;
+ (BOOL)autosavesInPlace
{
return YES;
}
- (id)init
{
self = [super init];
if (self) {
self.textStorage = nil;
self.textView = nil;
textContentToLoad = [#"" retain];
}
return self;
}
- (NSString *)windowNibName
{
return #"MyTextDocument";
}
- (void)windowControllerDidLoadNib:(NSWindowController *)aController
{
[super windowControllerDidLoadNib:aController];
self.textStorage = self.textView.textStorage;
[self loadTextContentIntoStorage];
}
- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError
{
return [self.textStorage.string dataUsingEncoding:NSUTF8StringEncoding];
}
- (BOOL)readFromData:(NSData *)data ofType:(NSString *)typeName error:(NSError **)outError
{
textContentToLoad = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
if (!textContentToLoad) {
*outError = [NSError errorWithDomain:NSCocoaErrorDomain code:NSFileReadUnknownError userInfo:nil];
return NO;
}
[self loadTextContentIntoStorage];
return YES;
}
- (void)loadTextContentIntoStorage
{
if (!self.textStorage || !textContentToLoad)
return;
[self.textStorage beginEditing];
[self.textStorage replaceCharactersInRange:NSMakeRange(0, self.textStorage.length) withString:textContentToLoad];
[textContentToLoad release], textContentToLoad = nil;
}
#end

Answer 1

Is your plist set up correctly when it comes to types?
It appears that NSDocument passes the result of [self fileNameExtensionForType:[self autosavingFileType] saveOperation:NSAutosaveElsewhereOperation] to stringByAppendingPathExtension: (the method that's throwing the exception here). If your app returns nil for this expression, then this exception may result.
You should probably file a bug at Apple for this, but in the meantime, make sure your app returns something non-nil.

Answer 2

Paste this into you document class (e.g. Document.m):
-(NSString*)fileNameExtensionForType:(NSString *)typeName saveOperation: (NSSaveOperationType)saveOperation
{
return #"yourAutosaveExtension";
}
Before, like kperryua said, this method was not implemented and returned nil.