我有一个使用 Core Data 的项目。它有一个 Note 对象，该对象具有一个称为内容的可转换属性。我将 NSAttributedString 存储到此属性中。该属性在第一次保存时保存得很好，但是当我尝试创建第二个笔记对象时，应用程序崩溃了。
这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];
}
同样，当持久存储中没有对象时，此代码可以毫无问题地保存。
当我尝试保存新对象时（在非空存储中：）首先抛出此异常（我为所有异常设置了断点）-[NSConcreteMutableAttributedString compare:]: unrecognized selector sent to instance 0x1759e8b0
然后当我继续时，我得到了这个：
2013-07-18 10:17:39.011 Meta[2417:60b] CoreData：错误：严重的应用程序错误。在核心数据更改处理期间捕获到异常。这通常是 NSManagedObjectContextObjectsDidChangeNotification 观察者中的一个错误。-[NSConcreteMutableAttributedString compare:]: 无法识别的选择器发送到实例 0x1759e8b0 与 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 compare:]：无法识别的选择器发送到实例 0x1759e8b0'
我还使用了一个 NSManagedObject 子类，它的实现方式如下：
@interface Note : NSManagedObject
@property (nonatomic, strong) id content;
@end
同样，内容是我试图存储属性字符串的地方
我尝试使用默认的 NSValueTransformer 和我自己的子类。两者都会导致同样的问题。
编辑：这是我的价值转换器的实现：
#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：这是回溯：
(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