Realm, Object has been deleted or invalidated - ios

Question

I am trying to build an new iOS app and am using the RxSwift Library and Realm as database.
I build a tableview which shows a list of object from realm and these object should be editable and can be removed. (I don't use the tableview editing capabilities for this.)
Now when I remove an item from the table the table should refresh because i used RxSwift to bind the tableview to the Realm results. But instead of updating it crashes the app.
The error I get when the app crashes is 'RLMException', reason: 'Object has been deleted or invalidated.'
Also I get a stack trace in the output, but I can't find the source / reason why the crash happens.
Output stacktrace:
2018-05-14 00:09:34.660634+0200 RealmTest[65540:4239839] *** Terminating app due to uncaught exception 'RLMException', reason: 'Object has been deleted or invalidated.'
*** First throw call stack:
(
0 CoreFoundation 0x000000010f76e1e6 __exceptionPreprocess + 294
1 libobjc.A.dylib 0x000000010ee03031 objc_exception_throw + 48
2 Realm 0x000000010d44abd3 _ZL17RLMVerifyAttachedP13RLMObjectBase + 83
3 Realm 0x000000010d44c89c _ZN12_GLOBAL__N_18getBoxedIN5realm10StringDataEEEP11objc_objectP13RLMObjectBasem + 28
4 Realm 0x000000010d44c877 ___ZN12_GLOBAL__N_115makeBoxedGetterIN5realm10StringDataEEEP11objc_objectm_block_invoke + 39
5 RealmTest 0x000000010cf9c6a9 _T09RealmTest0B9ModelItemV8identitySSvg + 41
6 RealmTest 0x000000010cf9c6f5 _T09RealmTest0B9ModelItemV14Differentiator16IdentifiableTypeAadEP8identity8IdentityQzvgTW + 21
7 Differentiator 0x000000010d29f24e _T014Differentiator4DiffO23calculateAssociatedData33_D199D3FBF4B7CA3AFA95223EE09B4772LLs15ContiguousArrayVyAGyAC04ItemdE0AELLVGG_AKtAGyAGyxGG07initialP5Cache_AM05finalpR0tKAA16IdentifiableTypeRzlFZ + 2094
8 Differentiator 0x000000010d2ac30e _T014Differentiator4DiffO16CommandGenerator33_D199D3FBF4B7CA3AFA95223EE09B4772LLV22calculateItemMovementss15ContiguousArrayVyAIyAC0N14AssociatedDataAELLVGG_AMtAIyAIy0N0QzGG07initialN5Cache_AQ05finalnU0AIyAC07SectionrS0AELLVG0twS0AV0vwS0tKFZ + 334
9 Differentiator 0x000000010d2a1d65 _T014Differentiator4DiffO16CommandGenerator33_D199D3FBF4B7CA3AFA95223EE09B4772LLV27generatorForInitialSectionsAFy_xGSayxG_AI05finalP0tKFZ + 1253
10 Differentiator 0x000000010d2a1395 _T014Differentiator4DiffO27differencesForSectionedViewSayAA9ChangesetVyxGGSayxG15initialSections_AI05finalI0tKAA26AnimatableSectionModelTypeRzlFZ + 277
11 RxDataSources 0x000000010e35ede4 _T013RxDataSources0a26TableViewSectionedAnimatedB6SourceC05tableE0ySo07UITableE0C_0A5Swift5EventOySayxGG08observedL0tFyACyxG_AJtcfU_yycfU_ + 660
12 RxDataSources 0x000000010e360049 _T013RxDataSources0a26TableViewSectionedAnimatedB6SourceC05tableE0ySo07UITableE0C_0A5Swift5EventOySayxGG08observedL0tFyACyxG_AJtcfU_yycfU_TA + 25
13 RxDataSources 0x000000010e35f63d _T0Ieg_IeyB_TR + 45
14 libdispatch.dylib 0x0000000113b5b807 _dispatch_call_block_and_release + 12
15 libdispatch.dylib 0x0000000113b5c848 _dispatch_client_callout + 8
16 libdispatch.dylib 0x0000000113b6792b _dispatch_main_queue_callback_4CF + 628
17 CoreFoundation 0x000000010f730c99 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
18 CoreFoundation 0x000000010f6f4ea6 __CFRunLoopRun + 2342
19 CoreFoundation 0x000000010f6f430b CFRunLoopRunSpecific + 635
20 GraphicsServices 0x0000000117bb5a73 GSEventRunModal + 62
21 UIKit 0x000000010fbeb0b7 UIApplicationMain + 159
22 RealmTest 0x000000010cf9a0a7 main + 55
23 libdyld.dylib 0x0000000113bd9955 start + 1
24 ??? 0x0000000000000001 0x0 + 1
)
My question is if somebody knows what I do wrong and wat the correct way of removing an realm object is using RxSwift and Databinding?
Edit:
I Made a small test project and put it on my github, it errors when you tab the deleteFirst button. https://github.com/Hiiragisan09/ios-example-project-realm-test

Answer 1

I found the solution my self.
When I started using Realm I didn't know that the object mutates if you delete it.
It was a bit of a struggle because when realm crashes on 'realm object has been deleted or invalidated' it doesn't give a stacktrace of where you tried to access a property of the realmobject.
So when you delete an item from Realm it will trigger the table to get new items, and because the table is animated it will try to diff the new data with the old data. And when the Diff tries to access a property in the old data it will crash.
To fix the problem I created structs that represent the data in the table. So that when I delete a Realm object, the table will not crash because the Diff can still access the old data.
The way I use structs with Realm How to save a struct to realm in swift

Answer 2

I had the same issue. Then I read Martyn's answer. I gave him the upvote because triaging the problem was the hardest part for me. But I implemented a different solution than his. Adding a struct-based repository layer on top of my Realm data-model feels heavy given the scope of the problem.
My lighter-weight solution: I added a parameter to my collectionView reload method to control the reload animation. I default the param to true, and then override it & set it to false as needed. The collectionView doesn't try to access old / deleted Realm objects because it's not trying to animate the old elements off the view. Problem solved.
func displayRecipes(_ recipes: [Recipe], withAnimations: Bool = true) {
...
dataSource?.apply(snapshot, animatingDifferences: withAnimations)
}