Object changelisteners does not trigger if a linked object changes

Goal

Detect changes of nested objects of a single RealmObject using RealmChangeListener . Understand the differences between RealmChangeListener on RealmObject and RealmResults.

Expected Results

RealmChangeListener of a single RealmObject would listen to changes of its nested objects. RealmChangeListener of a single RealmObject would listen to more changes than the RealmChangeListener of RealmResults.

Actual Results

RealmChangeListener of a single RealmObject doesn’t listen to changes of its nested objects. RealmChangeListener of RealmResults listens to changes of its children’s nested objects.

Steps & Code to Reproduce

I created a simple Android project to reproduce my use case: https://github.com/jpmcosta/RealmTestProject/tree/262ee9099b47852c2b26bc2f7e3874c8670e6264

Schema:

• App object contains a RealmColor property. That’s just a (bad) pattern to illustrate the issue.

How to reproduce the issue:

• there’s a list with a single App object
• click on that object to randomly change the value of its RealmColor property
• when RealmColor.value changes we want to:
  • change the App text color
  • change the FAB color

To change the App text color we add RealmChangeListener to RealmResults<App> and call notifyDatasetChanged when a change is detected. To change the FAB color we add a RealmChangeListener to the App object and update its color when a change is detected.

Issue:

• The FAB color is not updated properly.

Version of Realm and tooling

Realm version: 3.3.2

[jpmcosta]

@Zhuinden yes, that would work. I understand that App itself has not changed. But then, why does the RealmChangeListener in RealmResults<App> detect a change? Also, if I have 10 nested objects, should I need to add 10 different listeners?

[jpmcosta]

we’re not sure why it worked for me but it did

You probably were updating the parent object in the same transaction, without really thinking about it.

I want to get notified, when a nested object changes. Is this possible?

My ugly solution is to update the parent object “manually”. Usually, I have an updatedAt: Long property in the parent, which the child object is responsible to update whenever it is updated.