title: Realm object has been deleted or invalidated
body: <p>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.</p>
  
  <p>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:</p>
  
  <pre><code>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
  </code></pre>
  
  <p>This call stack lets me assume, that it's because of my write access in FavoriteLeaguesViewController's <code>generateLeagueList</code> method. The following is its body:</p>
  
  <pre><code>var favorites = FavoritesHelper.sharedInstance.favoriteLeagues
  favorites.sort { $0.sport &lt; $1.sport }
  
  for favorite in favorites {
    // Add to array, which we can later use for cellForRowAtIndexPath
  }
  </code></pre>
  
  <p><code>favorites</code> is of the type <code>[League]</code>, where <code>League</code> is a Realm Object. I'd assume the exception occurs because I'm accessing properties of the <code>League</code> 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).</p>
  
  <p>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 <code>League</code> objects prior to deleting them?</p>