ios - Extremely Odd Crash When saving a transformable NSAttributedString into Core Data -

i have project using core data. has note object has 1 transformable attribute called content. storing nsattributedstring property. property saves fine first save, when try create second note object, app crashes.

here code use save:

- (ibaction)save:(id)sender {       note* newnote = [nsentitydescription insertnewobjectforentityforname:@"note"     inmanagedobjectcontext:[self managedobjectcontext]];     nsattributedstring* string = [[self textview]attributedtext];      [newnote setcontent:string];     nsarray* tokens = [[self tokenfield]tokens];      nserror* error = nil;      if (![[self managedobjectcontext]save:&error]) {         nslog(@"error saving %@",[error localizeddescription]);     }     [[self navigationcontroller]popviewcontrolleranimated:yes]; } 

again code saves no problem when there no objects in persistent store.
when attempt save new object (in non empty store:) exception thrown first (i have break point set exceptions) -[nsconcretemutableattributedstring compare:]: unrecognized selector sent instance 0x1759e8b0

then when continue, this:

2013-07-18 10:17:39.011 meta[2417:60b] coredata: error: serious application error. exception caught during core data change processing. bug within observer of nsmanagedobjectcontextobjectsdidchangenotification. -[nsconcretemutableattributedstring compare:]: unrecognized selector sent instance 0x1759e8b0 userinfo (null) 2013-07-18 10:17:39.014 meta[2417:60b] *** terminating app due uncaught exception 'nsinvalidargumentexception', reason: '-[nsconcretemutableattributedstring compare:]: unrecognized selector sent instance 0x1759e8b0'

i using nsmanagedobject subclass implemented follows:

@interface note : nsmanagedobject  @property (nonatomic, strong) id content; @end 

again content attempting store attributed string

i have tried using default nsvaluetransformer , own subclass. both cause same problem.

edit: here implementation of value transformer:

#import "attributedstringvaluetransformer.h"  @implementation attributedstringvaluetransformer +(class)transformedvalueclass {     return [nsattributedstring class]; } +(void)initialize {     [nsvaluetransformer setvaluetransformer:[[self alloc]init] forname:@"nsattributedstringvaluetransformer"]; }  +(bool)allowsreversetransformation {     return yes; }  -(nsdata*)transformedvalue:(nsattributedstring*)value {     nsdata* stringasdata = [nskeyedarchiver archiveddatawithrootobject:value];     return stringasdata; }  -(nsattributedstring*)reversetransformedvalue:(nsdata*)value {     nsattributedstring* string = [nskeyedunarchiver unarchiveobjectwithdata:value];      return string; } 

edit: here backtrace:

(lldb) bt * thread #1: tid = 0x5d2ef, 0x39a3d688 libobjc.a.dylib`objc_exception_throw, queue = 'com.apple.main-thread, stop reason = breakpoint 1.1     frame #0: 0x39a3d688 libobjc.a.dylib`objc_exception_throw     frame #1: 0x2f958fa2 corefoundation`-[nsobject(nsobject) doesnotrecognizeselector:] + 202     frame #2: 0x2f95787a corefoundation`___forwarding___ + 706     frame #3: 0x2f8a5528 corefoundation`__forwarding_prep_0___ + 24     frame #4: 0x302a5d48 foundation`_nscompareobject + 32     frame #5: 0x3034fe7e foundation`-[nssortdescriptor compareobject:toobject:] + 270     frame #6: 0x2f79e5f4 coredata`+[nsfetchedresultscontroller(privatemethods) _insertindexforobject:inarray:lowidx:highidx:sortdescriptors:] + 216     frame #7: 0x2f79ada6 coredata`-[nsfetchedresultscontroller(privatemethods) _postprocessinsertedobjects:] + 514     frame #8: 0x2f79c842 coredata`-[nsfetchedresultscontroller(privatemethods) _managedobjectcontextdidchange:] + 1898     frame #9: 0x2f89c836 corefoundation`_cfxnotificationpost + 1718     frame #10: 0x302a13b0 foundation`-[nsnotificationcenter postnotificationname:object:userinfo:] + 76     frame #11: 0x2f72280a coredata`-[nsmanagedobjectcontext(_nsinternalnotificationhandling) _postobjectsdidchangenotificationwithuserinfo:] + 78     frame #12: 0x2f721b0a coredata`-[nsmanagedobjectcontext(_nsinternalchangeprocessing) _createandpostchangenotification:withdeletions:withupdates:withrefreshes:] + 298     frame #13: 0x2f6a0af6 coredata`-[nsmanagedobjectcontext(_nsinternalchangeprocessing) _processrecentchanges:] + 2346     frame #14: 0x2f7159ba coredata`-[nsmanagedobjectcontext save:] + 190     frame #15: 0x00106f82 meta`-[newnoteviewcontroller save:](self=0x15dd2030, _cmd=0x325ba35a, sender=0x15dc5a70) + 918 @ newnoteviewcontroller.m:176     frame #16: 0x320482a2 uikit`-[uiapplication sendaction:to:from:forevent:] + 90     frame #17: 0x32048330 uikit`-[uibarbuttonitem(uiinternal) _sendaction:withevent:] + 120     frame #18: 0x320482a2 uikit`-[uiapplication sendaction:to:from:forevent:] + 90     frame #19: 0x32048242 uikit`-[uiapplication sendaction:totarget:fromsender:forevent:] + 30     frame #20: 0x32048220 uikit`-[uicontrol sendaction:to:forevent:] + 44     frame #21: 0x3217cfce uikit`-[uicontrol _sendactionsforevents:withevent:] + 374     frame #22: 0x32048036 uikit`-[uicontrol touchesended:withevent:] + 590     frame #23: 0x31f830e0 uikit`-[uiwindow _sendtouchesforevent:] + 528     frame #24: 0x31f718f0 uikit`-[uiapplication sendevent:] + 196     frame #25: 0x32114406 uikit`_uiapplicationhandlehidevent + 6262     frame #26: 0x306765ce iokit`__iohideventsystemclientqueuecallback + 222     frame #27: 0x2f911f04 corefoundation`__cfmachportperform + 136     frame #28: 0x2f91d206 corefoundation`__cfrunloop_is_calling_out_to_a_source1_perform_function__ + 34     frame #29: 0x2f91d1a2 corefoundation`__cfrunloopdosource1 + 346     frame #30: 0x2f91b966 corefoundation`__cfrunlooprun + 1398     frame #31: 0x2f892446 corefoundation`cfrunlooprunspecific + 522     frame #32: 0x2f89222a corefoundation`cfrunloopruninmode + 106     frame #33: 0x343f06da graphicsservices`gseventrunmodal + 138     frame #34: 0x31fbae00 uikit`uiapplicationmain + 1136     frame #35: 0x00105374 meta`main(argc=1, argv=0x27d07d1c) + 116 @ main.m:16 

found it:

* thread #1: tid = 0x5d2ef, 0x39a3d688 libobjc.a.dylib`objc_exception_throw, queue = 'com.apple.main-thread, stop reason = breakpoint 1.1     frame #0: 0x39a3d688 libobjc.a.dylib`objc_exception_throw     frame #1: 0x2f958fa2 corefoundation`-[nsobject(nsobject) doesnotrecognizeselector:] + 202     frame #2: 0x2f95787a corefoundation`___forwarding___ + 706     frame #3: 0x2f8a5528 corefoundation`__forwarding_prep_0___ + 24     frame #4: 0x302a5d48 foundation`_nscompareobject + 32     frame #5: 0x3034fe7e foundation`-[nssortdescriptor compareobject:toobject:] + 270**     frame #6: 0x2f79e5f4 coredata`+[nsfetchedresultscontroller(privatemethods) _insertindexforobject:inarray:lowidx:highidx:sortdescriptors:] + 216     frame #7: 0x2f79ada6 coredata`-[nsfetchedresultscontroller(privatemethods) _postprocessinsertedobjects:] + 514     frame #8: 0x2f79c842 coredata`-[nsfetchedresultscontroller(privatemethods) _managedobjectcontextdidchange:] + 1898 

as save happened, fetched results controller started update tableview (which on presenting view controller).

i have tableview controller subclass use easy setup takes sort descriptor key (as string) , internally turns array , sets fetch request.

[self setsortdescriptorkey:@"content"]; 

content transformable attribute in data model (transforms nsattributedstring). normal string, needed store attribute data well. after changing it, frc sending compare it. fixed changing sort descriptor key:

[self setsortdescriptorkey:@"content.string"];