领域对象已被删除或无效

Question

启动应用程序时，我将执行API调用以查看是否有可用的新数据。数据存储在我的本地Realm数据库中，其中一些显示在初始表视图控制器中。

API调用完成后，我将检查是否满足某些条件，这些条件要求我从数据库中删除一堆先前的数据，然后创建新对象。但是，当我删除旧数据时，我的应用程序崩溃，但出现以下异常：

2015-08-06 11:56:32.057 MSUapp[19754:172864] *** Terminating app due to uncaught exception 'RLMException', reason: 'Object has been deleted or invalidated.'
*** First throw call stack:
(
0   CoreFoundation                      0x000000010660cc65 __exceptionPreprocess + 165
1   libobjc.A.dylib                     0x00000001083bdbb7 objc_exception_throw + 45
2   Realm                               0x0000000105b78e95 _ZL17RLMVerifyAttachedP13RLMObjectBase + 85
3   Realm                               0x0000000105b7878d _ZL10RLMGetLinkP13RLMObjectBasemP8NSString + 29
4   Realm                               0x0000000105b7c23e ___ZL17RLMAccessorGetterP11RLMProperty15RLMAccessorCodeP8NSString_block_invoke_12 + 46
5   MSUapp                              0x0000000105764867 _TFFC6MSUapp29FavoriteLeaguesViewController18generateLeagueListFS0_FT_T_U_FTCS_6LeagueS1__Sb + 39
6   MSUapp                              0x00000001057648eb _TTRXFo_oC6MSUapp6LeagueoS0__dSb_XFo_iS0_iS0__dSb_ + 27
7   libswiftCore.dylib                  0x0000000108674ae2 _TFSs14_insertionSortUSs21MutableCollectionType_USs13GeneratorType__Ss22BidirectionalIndexType_Ss18_SignedIntegerType_Ss33_BuiltinIntegerLiteralConvertible____FTRQ_GVSs5RangeQQ_5Index_RFTQQQ_9Generator7ElementS7__Sb_T_ + 1570
8   libswiftCore.dylib                  0x0000000108676682 _TFSs14_introSortImplUSs21MutableCollectionType_USs13GeneratorType__Ss21RandomAccessIndexType_Ss18_SignedIntegerType_Ss33_BuiltinIntegerLiteralConvertible_Ss16SignedNumberType_S3_____FTRQ_GVSs5RangeQQ_5Index_RFTQQQ_9Generator7ElementS8__SbSi_T_ + 1250
9   libswiftCore.dylib                  0x0000000108676172 _TFSs10_introSortUSs21MutableCollectionType_USs13GeneratorType__Ss21RandomAccessIndexType_Ss18_SignedIntegerType_Ss33_BuiltinIntegerLiteralConvertible_Ss16SignedNumberType_S3_____FTRQ_GVSs5RangeQQ_5Index_FTQQQ_9Generator7ElementS8__Sb_T_ + 1058
10  libswiftCore.dylib                  0x00000001085ec947 _TFSs4sortUSs21MutableCollectionType_USs13GeneratorType__Ss21RandomAccessIndexType_Ss18_SignedIntegerType_Ss33_BuiltinIntegerLiteralConvertible_Ss16SignedNumberType_S3_____FTRQ_FTQQQ_9Generator7ElementS6__Sb_T_ + 471
11  libswiftCore.dylib                  0x00000001086a8d9e _TPA__TFFSa4sortU__FRGSaQ__FFTQ_Q__SbT_U_FRGVSs26UnsafeMutableBufferPointerQ__T_ + 222
12  libswiftCore.dylib                  0x00000001086a8e18 _TPA__TTRG0_R_XFo_lGVSs26UnsafeMutableBufferPointerq___dT__XFo_lGS_q___iT__42 + 56
13  libswiftCore.dylib                  0x00000001085f7fda _TFSa30withUnsafeMutableBufferPointerU__fRGSaQ__U__FFRGVSs26UnsafeMutableBufferPointerQd___Q_Q_ + 522
14  libswiftCore.dylib                  0x00000001085f7db4 _TFSa4sortU__fRGSaQ__FFTQ_Q__SbT_ + 132
15  MSUapp                              0x0000000105761709 _TFC6MSUapp29FavoriteLeaguesViewController18generateLeagueListfS0_FT_T_ + 1097
16  MSUapp                              0x000000010576354b _TFC6MSUapp29FavoriteLeaguesViewController27numberOfSectionsInTableViewfS0_FCSo11UITableViewSi + 59
17  MSUapp                              0x00000001057635fa _TToFC6MSUapp29FavoriteLeaguesViewController27numberOfSectionsInTableViewfS0_FCSo11UITableViewSi + 58
18  UIKit                               0x000000010737cac3 -[UITableViewRowData _updateNumSections] + 84
19  UIKit                               0x000000010737d4b4 -[UITableViewRowData invalidateAllSections] + 69
20  UIKit                               0x00000001071c873b -[UITableView _updateRowData] + 217
21  UIKit                               0x00000001071de2b7 -[UITableView noteNumberOfRowsChanged] + 112
22  UIKit                               0x00000001071dd9f5 -[UITableView reloadData] + 1355
23  MSUapp                              0x00000001057647c6 _TFFC6MSUapp29FavoriteLeaguesViewController11viewDidLoadFS0_FT_T_U_FTO10RealmSwift12NotificationCS1_5Realm_T_ + 166
24  RealmSwift                          0x0000000105f37210 _TFF10RealmSwift41rlmNotificationBlockFromNotificationBlockFFT12notificationOS_12Notification5realmCS_5Realm_T_bTSSCSo8RLMRealm_T_U_FTSSS2__T_ + 224
25  RealmSwift                          0x0000000105f372af _TTRXFo_oSSoCSo8RLMRealm_dT__XFdCb_dCSo8NSStringdS__dT__ + 111
26  Realm                               0x0000000105c0645a -[RLMRealm sendNotifications:] + 986
27  Realm                               0x0000000105c068e6 -[RLMRealm commitWriteTransaction] + 262
28  Realm                               0x0000000105c06a48 -[RLMRealm transactionWithBlock:] + 120
29  RealmSwift                          0x0000000105f34250 _TFC10RealmSwift5Realm5writefS0_FFT_T_T_ + 176
30  MSUapp                              0x00000001056d46db _TZFC6MSUapp14DatabaseHelper23removeForSportAndSeasonfMS0_FTCS_5Sport6seasonSS_T_ + 603
31  MSUapp                              0x0000000105710d22 _TFFFC6MSUapp11AppDelegate14loadRemoteDataFS0_FT_T_U_FGSaCS_5Sport_T_U_FGSaCS_6League_T_ + 866
32  MSUapp                              0x0000000105710dc7 _TTRXFo_oGSaC6MSUapp6League__dT__XFo_iGSaS0___iT__ + 23
33  MSUapp                              0x00000001057103d1 _TPA__TTRXFo_oGSaC6MSUapp6League__dT__XFo_iGSaS0___iT__ + 81
34  MSUapp                              0x000000010575de90 _TTRXFo_iGSaC6MSUapp6League__iT__XFo_oGSaS0___dT__ + 32
35  MSUapp                              0x000000010575ddeb _TFZFC6MSUapp9APIHelper11loadLeaguesFMS0_FTSi18shouldWriteToRealmSb10completionGSqFGSaCS_6League_T___T_U_FCSo6NSDataT_ + 2763
36  MSUapp                              0x00000001056f4a0e _TTSf2n_n_n_n_n_d_i_n_n_n___TFFC6MSUapp14JSONDataSource18loadRemoteJsonDataFS0_FTSSCS_19GETParameterBuilderFCSo6NSDataT__T_U_FTCSo12NSURLRequestGSqCSo17NSHTTPURLResponse_GSqS2__GSqCSo7NSError__T_ + 2302
37  MSUapp                              0x00000001056f2d59 _TPA__TTSf2n_n_n_n_n_d_i_n_n_n___TFFC6MSUapp14JSONDataSource18loadRemoteJsonDataFS0_FTSSCS_19GETParameterBuilderFCSo6NSDataT__T_U_FTCSo12NSURLRequestGSqCSo17NSHTTPURLResponse_GSqS2__GSqCSo7NSError__T_ + 249
38  Alamofire                           0x00000001059e7599 _TTRXFo_oCSo12NSURLRequestoGSqCSo17NSHTTPURLResponse_oGSqCSo6NSData_oGSqCSo7NSError__dT__XFo_oS_oGSqS0__iGSqS1__oGSqS2___dT__ + 25
39  Alamofire                           0x00000001059e7461 _TFFFC9Alamofire7Request8responseFDS0_US_18ResponseSerializer___FT5queueGSqCSo8NSObject_18responseSerializerQ_17completionHandlerFTCSo12NSURLRequestGSqCSo17NSHTTPURLResponse_GSqQ0__GSqCSo7NSError__T__DS0_U_FT_T_U_FT_T_ + 737
40  Alamofire                           0x00000001059e690e _TPA__TFFFC9Alamofire7Request8responseFDS0_US_18ResponseSerializer___FT5queueGSqCSo8NSObject_18responseSerializerQ_17completionHandlerFTCSo12NSURLRequestGSqCSo17NSHTTPURLResponse_GSqQ0__GSqCSo7NSError__T__DS0_U_FT_T_U_FT_T_ + 206
41  Alamofire                           0x00000001059a89d7 _TTRXFo__dT__XFdCb__dT__ + 39
42  libdispatch.dylib                   0x000000010938b186 _dispatch_call_block_and_release + 12
43  libdispatch.dylib                   0x00000001093aa614 _dispatch_client_callout + 8
44  libdispatch.dylib                   0x0000000109392a1c _dispatch_main_queue_callback_4CF + 1664
45  CoreFoundation                      0x00000001065741f9 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
46  CoreFoundation                      0x0000000106535dcb __CFRunLoopRun + 2043
47  CoreFoundation                      0x0000000106535366 CFRunLoopRunSpecific + 470
48  GraphicsServices                    0x000000010cc17a3e GSEventRunModal + 161
49  UIKit                               0x00000001070f08c0 UIApplicationMain + 1282
50  MSUapp                              0x000000010570f857 main + 135
51  libdyld.dylib                       0x00000001093df145 start + 1
52  ???                                 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

该调用堆栈让我假设，这是由于我在FavoriteLeaguesViewController的generateLeagueList方法中具有写访问权限。其主体如下：

var favorites = FavoritesHelper.sharedInstance.favoriteLeagues
favorites.sort { $0.sport < $1.sport }

for favorite in favorites {
  // Add to array, which we can later use for cellForRowAtIndexPath
}

favorites类型为[League]，其中League是领域对象。我以为发生异常是因为我正在访问League对象的属性，这些对象的属性已同时从Realm数据库中删除（因为已经在AppDelegate中启动的API调用已完成）。

那么我的问题是：如何防止这种情况发生？League在删除对象之前，如何确保没有对任何对象的写入/读取权限？

Answer 1

问题在我FavoritesHelper班上。它同时具有favoriteLeagueIDs和favoriteLeagues属性。每当我想要这些联赛的一些数据时，我总是将它们都设置好，并将这些ID用于内部使用，并将另一个属性用于其他用途。

这意味着，favoriteLeagues（属性[League]）的属性会不断引用所有喜欢的联赛，因此当我想要在无效后获取它们时，应用程序就会崩溃。

为了解决这个问题，我要做的就是将属性更改favoriteLeagues为计算属性，如下所示：

var favoriteLeagues: [League] {
    get {
        var leagues = [League]()
        for id in favoriteLeagueIDs {
            if let league = realm.objectForPrimaryKey(League.self, key: id) {
                leagues.append(league)
            }
        }
        return leagues
    }
}

现在不再需要引用联赛，而是在需要阅读联赛时从数据库中加载它们。无效或删除的对象由于该if let语句而不会被加载（在这种情况下该Realm.objectForPrimaryKey(:key:)方法将返回nil）。