Padarom Padarom - 9 days ago 7
Swift Question

Realm object has been deleted or invalidated

When I start my app, I perform an API call to see whether there's new data available. The data is stored in my local Realm database, and some of it is displayed in the initial table view controller.

Once the API call is finished, I check if some conditions are met that require me to delete a bunch of the previous data from the database and then create new objects. However, when I delete the old data, my app crashes with the following exception:

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


This call stack lets me assume, that it's because of my write access in FavoriteLeaguesViewController's
generateLeagueList
method. The following is its body:

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
is of the type
[League]
, where
League
is a Realm Object. I'd assume the exception occurs because I'm accessing properties of the
League
objects, which have been deleted from the Realm database in the mean time (because the API call that has been started in the AppDelegate is now finished).

My question then is: How can I prevent this from happening? How can I make sure that there's no more writing/reading-access to any of the
League
objects prior to deleting them?

Answer

The issue was in my FavoritesHelper class. It had both a favoriteLeagueIDs and favoriteLeagues property. I always set both of them and used the IDs for internal usage and the other property for whenever I want some data from these leagues.

This meant, that all favorite leagues were constantly referenced by the favoriteLeagues property (of the type [League]), thus crashing the app when I wanted to fetch them after they're invalidated.

What I've done to fix this, was to change the property favoriteLeagues to a computed property as follows:

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
    }
}

Now the leagues are no longer referenced and just get loaded from the database when I need to read them. Invalidated or deleted objects don't get loaded because of the if let statement (the Realm.objectForPrimaryKey(:key:) method returns nil in such a case).

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