我在尝试从[__NSCFArray objectForKey:]: unrecognized selector sent to instance获取某些数据时收到错误Core Data。
我对iOS编程比较陌生，并且不太了解这个错误试图告诉我的内容。我设置exception breakpoint来确定哪条线给我的问题，这就是这行代码：
if let fetchResults = managedObjectContext!.executeFetchRequest(fetchRequest, error: nil) as? [User] {
为什么我会收到此错误，如何解决？这与我保存Core Data的方式有关吗？我刚刚做了一个更改，我从服务器收到JSON，然后在后台处理，最后在主线程中保存对ManagedObjectContext的更改。
func getUser(userId: String) -> User? {
let fetchRequest = NSFetchRequest(entityName: "User")
fetchRequest.predicate = NSPredicate(format: "userId == %@", userId)
fetchRequest.fetchLimit = 1
if let fetchResults = managedObjectContext!.executeFetchRequest(fetchRequest, error: nil) as? [User] {
if !fetchResults.isEmpty {
return fetchResults[0]
}
else {
println("UserId \(userId) not in database")
}
}
return nil
}
错误
2014-12-06 13:09:36.087 LFDate[3162:51570] -[__NSCFArray objectForKey:]: unrecognized selector sent to instance 0x7fb9e95c4310
2014-12-06 13:09:36.090 LFDate[3162:51570] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFArray objectForKey:]: unrecognized selector sent to instance 0x7fb9e95c4310'
*** First throw call stack:
(
0 CoreFoundation 0x00000001025c2f35 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x000000010465ebb7 objc_exception_throw + 45
2 CoreFoundation 0x00000001025ca04d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3 CoreFoundation 0x000000010252227c ___forwarding___ + 988
4 CoreFoundation 0x0000000102521e18 _CF_forwarding_prep_0 + 120
5 CoreFoundation 0x000000010248beaf CFDictionaryGetValue + 159
6 Foundation 0x0000000102befd78 -[NSKeyedUnarchiver initForReadingWithData:] + 1698
7 Foundation 0x0000000102c135ea +[NSKeyedUnarchiver unarchiveObjectWithData:] + 66
8 CoreData 0x000000010210b4e0 _prepareResultsFromResultSet + 3552
9 CoreData 0x0000000102108930 newFetchedRowsForFetchPlan_MT + 3296
10 CoreData 0x00000001020f53ac -[NSSQLCore objectsForFetchRequest:inContext:] + 524
11 CoreData 0x00000001020f4e2b -[NSSQLCore executeRequest:withContext:error:] + 299
12 CoreData 0x00000001021ca4f3 __65-[NSPersistentStoreCoordinator executeRequest:withContext:error:]_block_invoke + 3331
13 CoreData 0x00000001021d27ee gutsOfBlockToNSPersistentStoreCoordinatorPerform + 190
14 libdispatch.dylib 0x00000001052117f4 _dispatch_client_callout + 8
15 libdispatch.dylib 0x00000001051f8774 _dispatch_barrier_sync_f_invoke + 365
16 CoreData 0x00000001021c53d5 _perform + 197
17 CoreData 0x00000001020f4ac8 -[NSPersistentStoreCoordinator executeRequest:withContext:error:] + 504
18 CoreData 0x00000001020f33e0 -[NSManagedObjectContext executeFetchRequest:error:] + 544
19 LFDate 0x0000000101b9c3b3 _TFC6LFDate14DatabaseHelper7getUserfS0_FSSGSqCS_4User_ + 1075
20 LFDate 0x0000000101c4ce01 _TFC6LFDate23MenuTableViewController9tableViewfS0_FTCSo11UITableView21cellForRowAtIndexPathCSo11NSIndexPath_CSo15UITableViewCell + 4689
21 LFDate 0x0000000101c4e4ff _TToFC6LFDate23MenuTableViewController9tableViewfS0_FTCSo11UITableView21cellForRowAtIndexPathCSo11NSIndexPath_CSo15UITableViewCell + 79
22 UIKit 0x000000010349d4b3 -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] + 508
23 UIKit 0x000000010347cfb1 -[UITableView _updateVisibleCellsNow:isRecursive:] + 2846
24 UIKit 0x0000000103492e3c -[UITableView layoutSubviews] + 213
25 UIKit 0x000000010341f973 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 521
26 QuartzCore 0x000000010318ade8 -[CALayer layoutSublayers] + 150
27 QuartzCore 0x000000010317fa0e _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 380
28 QuartzCore 0x000000010317f87e _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24
29 QuartzCore 0x00000001030ed63e _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 242
30 QuartzCore 0x00000001030ee74a _ZN2CA11Transaction6commitEv + 390
31 QuartzCore 0x00000001030eedb5 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 89
32 CoreFoundation 0x00000001024f7dc7 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
33 CoreFoundation 0x00000001024f7d20 __CFRunLoopDoObservers + 368
34 CoreFoundation 0x00000001024edb53 __CFRunLoopRun + 1123
35 CoreFoundation 0x00000001024ed486 CFRunLoopRunSpecific + 470
36 GraphicsServices 0x00000001072f09f0 GSEventRunModal + 161
37 UIKit 0x00000001033a6420 UIApplicationMain + 1282
38 LFDate 0x0000000101be33ae top_level_code + 78
39 LFDate 0x0000000101be33ea main + 42
40 libdyld.dylib 0x0000000105246145 start + 1
41 ??? 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException