RealmChangeListener not called for RealmList of RealmObject

Goal

After adding a RealmChangeListener to a RealmList, if the number of its elements changes, the listener should be called.

Expected Results

RealmChangeListener should always be called when the number of elements of a RealmList changes.

Actual Results

RealmChangeListener is not always called when the number of elements of a RealmList changes.

Steps & Code to Reproduce

I created a simplified Android project to reproduce the issue’s workflow: https://github.com/jpmcosta/RealmTestProject/tree/9375194c255977ae944fde292b7ca5b9ba845f5a

The workflow of the issue:

• MainActivity opens a CreateActivity that starts CreateIntentService to add or remove items from a RealmList (then, CreateActivity is finished)
• when the MainActivity starts again, it adds a RealmChangeListener to the RealmList and logs its current number of items
• the listener’s onChange() method is not called, despite the number of items being changed (this is the issue)

To reproduce:

• run the app
• click on the floating action button to open CreateActivity and change the number of elements of the list
  • if the list is empty, it should fill the list with 10 items
  • if the list has items, it should clear all items
• logs are created when (log_tag: ItemListAdapter)
  • the RealmChangeListener is added: add listener <current number of items>
  • the RealmChangeListener is removed: remove listener
  • the RealmChangeListener.onChange(): onChange() <current number of items>
• to understand the issue:
  • notice the number of items when the listener is added, and compare it to the list’s actual number of items
  • notice whether or not onChange() was called (usually, it’s not called).
• you can also long press the floating action button to add a single item, to make sure the listener is working (it should work and a onChange() log should be created)

I’m reproducing the issue consistently, but not 100% of the time (maybe 99%). If you can’t reproduce the issue, try to change the Don't keep activities setting in Android’s Developer options.

Version of Realm and tooling

Realm version: 4.1.0

Android Studio version: 3.0

Which Android version and device: 7.1.2

[Zhuinden]

If you have custom item types in your Adapter then Realm doesn’t know about those. We ran into this by using getItemViewType for showing empty views, but that is not Realm bug ofc.

[cmelchior]

Yes, but the problem is not the recreation of the adapter as far as I can see. What I’m seeing is that a RealmListener on the Realm is triggered due to the background write, but the more specialized listener on realmlist is not.

This indicate that the problem is not around the adapter, but how the listeners work.

11-07 10:55:27.625 13292-13292/com.jpmcosta.test.realmtestproject I/REALM_JAVA: MainActivity: onStart()
11-07 10:55:27.625 13292-13292/com.jpmcosta.test.realmtestproject I/REALM_JAVA: Size of list: 10
11-07 10:55:27.663 13292-13292/com.jpmcosta.test.realmtestproject I/REALM_JAVA: onChange() called on Realm. Size: 0
<!-- The List specific  Listener should have been triggered here
11-07 10:55:27.759 13292-13292/com.jpmcosta.test.realmtestproject I/REALM_JAVA: getItemCount(): 0

Incidentally, converting the RealmList to RealmResults have the same error, but they use the same underlying mechanics so it isn’t entirely unsurprising.