Ios 将可转换的NSAttribute字符串保存到核心数据时发生异常崩溃

我有一个使用核心数据的项目。它有一个Note对象，该对象有一个称为content的可转换属性。我正在将NSAttributed字符串存储到此属性中。属性在第一次保存时可以很好地保存，但当我尝试创建第二个note对象时，应用程序崩溃

以下是我用来保存的代码：

- (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];
}

当持久性存储区中没有对象时，此代码再次保存，没有问题。
当我尝试保存一个新对象时（在非空存储中：），首先抛出此异常（我为所有异常设置了断点） -[NSContectEmustableAttributedString比较：]：发送到实例0x1759e8b0的选择器无法识别

然后，当我继续时，我得到：

2013-07-18 10:17:39.011元[2417:60b]核心数据：错误：严重的应用程序错误。在核心数据更改处理期间捕获异常。这通常是NSManagedObjectContextObjectsIDChangeNotification的观察者中的错误-[NSConcreteModableAttributedString compare::]：发送到实例0x1759e8b0的无法识别的选择器带有userInfo（null） 2013-07-18 10:17:39.014 Meta[2417:60b]***由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因：'-[NSConcreteMutableAttributedString比较：]：无法识别的选择器发送到实例0x1759e8b0'

我还使用了一个NSManagedObject子类，其实现如下：

@interface Note : NSManagedObject

@property (nonatomic, strong) id content;
@end

内容也是我试图存储属性字符串的地方

我已经尝试使用默认的NSValueTransformer和我自己的子类。两者都会导致相同的问题

编辑：以下是my value transformer的实现：

#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;
}

编辑：以下是回溯：

(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 at 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 at main.m:16

找到它：

* 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

保存时，获取的结果控制器开始更新tableview（位于显示视图控制器上）

我有一个tableview控制器子类，用于轻松设置，它接受排序描述符键（作为字符串），并在内部将其转换为数组并设置获取请求

[self setSortDescriptorKey:@"content"];

内容是数据模型中的可转换属性（转换NSAttribute字符串）。 最初它只是一个普通字符串，但我还需要存储属性数据。更改后，FRC将发送比较。我通过更改排序描述符键修复了它：

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

---

当抛出“unrecognized selector”异常时，查看回溯是什么样子会很有用。这很可能是核心问题，第二个例外是第一个例外的副作用。也，这可能有助于查看您的值转换器的外观。添加了值转换器植入和回溯。无论是使用值转换器还是让核心数据使用默认值，我都会得到相同的结果。我猜fetchedResultsController实现中有什么东西试图在对属性字符串排序时调用compare:tableView（位于导航堆栈上此视图之前的视图中）。排序描述符。听起来是个不错的猜测，排序描述符看起来像什么？它可能第一次起作用，因为对于一个对象没有排序，但是对于两个或更多的对象，描述符起作用。