-[NSKeyedUnarchiver decodeObjectForKey:]: cannot decode object of class (myCustomClass) - objective-c

Question

I'm new to objective-c and cocoa, and trying to create a document based application that saves and loads a custom class to and from the filesystem. My custom class that conforms to nscoding protocol is as follow:
NSString *const description = #"description";
#implementation PhotoItem
#synthesize description = _description;
-(id)init {
if(self = [super init]){
self.description = #"";
}
return self;
}
/* serializing into file */
- (void)encodeWithCoder:(NSCoder *)aCoder {
[aCoder encodeObject:self.description forKey:description];
}
/* deserializing */
- (id)initWithCoder:(NSCoder *)aDecoder {
self.description = [aDecoder decodeObjectForKey:description];
return self;
}
and my document:
#implementation AMRDocument
#synthesize imgMainImage = _imgMainImage, lblCreationDate = _lblCreationDate, photo=_photo,
txtDescription = _txtDescription;
- (id)init
{
self = [super init];
if (self) {
self.photo = [[PhotoItem alloc] init];
}
return self;
}
- (NSString *)windowNibName
{
return #"AMRDocument";
}
- (void)windowControllerDidLoadNib:(NSWindowController *)aController
{
NSLog(#"windowControllerDidLoadNib");
[super windowControllerDidLoadNib:aController];
// self.imgMainImage.image = self.photo.image;
[self.txtDescription setString: self.photo.description];
}
+ (BOOL)autosavesInPlace
{
return YES;
}
#pragma mark -saving and loading
- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError
{
// self.photo.image = self.imgMainImage.image;
// return [NSKeyedArchiver archivedDataWithRootObject:self.photo];
self.photo.description = self.txtDescription.string;
NSData *archivedData = [NSKeyedArchiver archivedDataWithRootObject:self.photo];
return archivedData;
}
- (BOOL)readFromData:(NSData *)data ofType:(NSString *)typeName error:(NSError **)outError
{
self.photo = [NSKeyedUnarchiver unarchiveObjectWithData:data];
return YES;
}
- (void)windowWillClose:(NSNotification *)notification {
}
- (IBAction)archiveClicked:(id)sender {
self.photo = [NSKeyedUnarchiver unarchiveObjectWithFile:[#"~/desktop/myphoto1.photo"
stringByExpandingTildeInPath]];
[self.txtDescription setString:self.photo.description];
}
- (IBAction)archiveClicked:(id)sender {
self.photo.description = self.txtDescription.string;
[NSKeyedArchiver archiveRootObject:self.photo toFile:[#"~/desktop/myphoto1.photo"
stringByExpandingTildeInPath]];
}
#end
As you can see I've created two actions called archiveClicked, and unarchiveClicked, one for writing and the other for reading from the file.
It works perfectly fine.
When I'm saving the document using command+s, it can also successfully writes to the file, or at least no exception is thrown then. But when I'm trying to open up the saved file, it'll give me following exception in a popup instead of running the application and loads from the disk.
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Application Specific Information:
*** Terminating app due to uncaught exception 'NSInvalidUnarchiveOperationException', reason: '*** -[NSKeyedUnarchiver decodeObjectForKey:]: cannot decode object of class (PhotoItem)'
terminate called throwing an exception
abort() called
Application Specific Backtrace 1:
0 CoreFoundation 0x00007fff8f715b06 __exceptionPreprocess + 198
1 libobjc.A.dylib 0x00007fff912f03f0 objc_exception_throw + 43
2 CoreFoundation 0x00007fff8f7158dc +[NSException raise:format:] + 204
3 Foundation 0x00007fff98a1e8c3 _decodeObjectBinary + 2559
4 Foundation 0x00007fff98a1dd24 _decodeObject + 226
5 Foundation 0x00007fff98a90df3 +[NSKeyedUnarchiver unarchiveObjectWithData:] + 92
6 DocumentBasedApp 0x0000000108e49a11 -[AMRDocument readFromData:ofType:error:] + 113
7 AppKit 0x00007fff8d764527 -[NSDocument readFromURL:ofType:error:] + 546
8 AppKit 0x00007fff8d365348 -[NSDocument _initWithContentsOfURL:ofType:error:] + 135
9 AppKit 0x00007fff8d364ff4 -[NSDocument initWithContentsOfURL:ofType:error:] + 262
10 AppKit 0x00007fff8d78d765 -[NSDocumentController makeDocumentWithContentsOfURL:ofType:error:] + 332
11 AppKit 0x00007fff8d78ce7f __block_global_12 + 230
12 AppKit 0x00007fff8d78ca1b __block_global_8 + 955
13 AppKit 0x00007fff8d78bdba -[NSDocumentController _openDocumentWithContentsOfURL:usingProcedure:] + 593
14 AppKit 0x00007fff8d78c655 __block_global_7 + 273
15 libdispatch.dylib 0x00007fff926b4f01 _dispatch_call_block_and_release + 15
16 libdispatch.dylib 0x00007fff926b10b6 _dispatch_client_callout + 8
17 libdispatch.dylib 0x00007fff926b60c8 _dispatch_main_queue_callback_4CF + 275
18 CoreFoundation 0x00007fff8f6b7b4c __CFRunLoopRun + 1644
19 CoreFoundation 0x00007fff8f6b70e2 CFRunLoopRunSpecific + 290
20 HIToolbox 0x00007fff8df91eb4 RunCurrentEventLoopInMode + 209
21 HIToolbox 0x00007fff8df91b94 ReceiveNextEventCommon + 166
22 HIToolbox 0x00007fff8df91ae3 BlockUntilNextEventMatchingListInMode + 62
23 AppKit 0x00007fff8d44c533 _DPSNextEvent + 685
24 AppKit 0x00007fff8d44bdf2 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 128
25 AppKit 0x00007fff8d4431a3 -[NSApplication run] + 517
26 AppKit 0x00007fff8d3e7bd6 NSApplicationMain + 869
27 DocumentBasedApp 0x0000000108e49652 main + 34
28 libdyld.dylib 0x00007fff8d2647e1 start + 0
I've actually created the actions to check the correctness of my nscoding functions and it seems to be working fine, but have no clue, and cannot find anything related to my issue.
Appreciate any help. Needless to say this is a part of my homework.
Edit:
name of this application is "PhotoManager". Earlier I had another document based app called "DocumentBasedApp", and the exception starts with :
Process: DocumentBasedApp [4852]
Path: /Users/USER/Library/Caches/*/DocumentBasedApp.app/Contents/MacOS/DocumentBasedApp
Identifier: com.cjcoax.DocumentBasedApp
Version: 1.0 (1)
Code Type: X86-64 (Native)
Parent Process: launchd [132]
User ID: 501

Answer 1

Your initWithCoder: needs to call [super init];.
- (id)initWithCoder:(NSCoder *)aDecoder {
self = [super init];
if (self) {
self.description = [aDecoder decodeObjectForKey:description];
}
return self;
}

Answer 2

The serialized version of MyCustomClass differs from the current version in your code, probably due to changes during development.
/Users/USER/Library/Caches/*/DocumentBasedApp.app/Contents/MacOS/DocumentBasedApp
Deleting the Cache directory got rid of the old serialized data.

Answer 3

Finally solved, I delete everything from the cache as I could not find following path:
/Users/USER/Library/Caches/*/DocumentBasedApp.app/Contents/MacOS/DocumentBasedApp
and it started working! Bizarre!

Answer 4

I had another problem with NSCoder's decodeObjectForKey method while using FXForm - it crashed without any explanation.
- (id)initWithCoder:(NSCoder *)decoder
{
if (self = [super init]) {
self.someObject = [decoder decodeObjectForKey:#"someObject"];
}
return self;
}
The reason was in memory issues. Commonly, looks like when there is no explanation of a bug in logs, it means, it's a memory issue. I forgot to use correct property attribute - copy. I used assign instead. This is correct code:
#interface MyClass : : NSObject <FXForm, NSCoding>
#property (nonatomic, copy) SomeClass *someObject;
#end
Just in case somebody meets this problem too.