Kotlin ConcurrentModificationException: when finding object from a list (Without removing any object or touching original list)

Question

I have a MutableList of "DisplayableMessage" unmanaged objects, and I want to find an object from this MutableList by property "messageId".

The code is in onBindViewHolder of a RecyclerViewAdapter:

val displayableMessage = displayableMessages?.find { item -> item?.messageId == message.id  }

When the main thread is running this line of code, The exception "java.util.ConcurrentModificationException" is raised.

The last 5 line of stack:

    at java.util.ArrayList$Itr.next(ArrayList.java:860)
    at MessagesAdapter.onBindViewHolder(MessagesAdapter.kt:279)
    at MessagesAdapter.onBindViewHolder(MessagesAdapter.kt:81)
    at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7059)
    at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7101)

MessagesAdapter.kt:279 is the code that I mentioned above.

As you see I'm not removing the list object nor touching the original list.

Edit v1: displayableMessages is referencing a mutable list that is created from detached realm results (This creation happens in another thread).

The code for detaching realm results:

val copiedMessages = Realm.getDefaultInstance().copyFromRealm(realmResults)

After this code, MutableList "list" is created from copiedMessages in another thread (because it includes reading from DB) and then displayableMessages is set to "list".

Then I use the main thread to notify that dataset was changed:

GlobalScope.launch(Dispatchers.Main) {
        notifyDataSetChanged()
    }

All these codes are run every time realmResults changes.

Managed/Unmanaged objects are instances of realmDB objects. Unmanaged objects are just like ordinary Java objects, they are not persisted and they will not be updated automatically. — Mohammad Jafari, Aug 24 '22 at 13:22
Especially the definition of `displayableMessages` would be useful — user3738870, Aug 24 '22 at 13:26
Is RealmDB managing the list that `displayMessages` is referencing. If so it might be changing it in another thread. — Michael Krussel, Aug 24 '22 at 21:36
I updated the question. As you can see displayableMessages is referencing a list that is created from detached realmResults. — Mohammad Jafari, Aug 25 '22 at 04:55

Kotlin ConcurrentModificationException: when finding object from a list (Without removing any object or touching original list)

0 Answers0