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

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 exce开发者_开发百科ption 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

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.

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.