DynamicData: [Bug]: Unexpected "Reset" Action in CollectionChanged Event When Adding data to ReadOnlyObservableCollection from SourceList

Describe the bug 🐞

When binding a DynamicData.SourceList to a ReadOnlyObservableCollection in a WPF application, and then adding data to the SourceList, the e.Action property in the CollectionChanged event of the ReadOnlyObservableCollection is reported as “Reset” instead of “Add.” However, when adding a data again to the SourceList, the e.Action property is reported as ‘Add’.

Code snippet: Properties:

private readonly SourceList<Person> _parentsSource = new SourceList<Person>();
public ReadOnlyObservableCollection<Person> Parents
{
    get;
}

Codes:

_parentsSource.Connect()
    .ObserveOn(RxApp.MainThreadScheduler)
    .Bind(out var parents)
    .Subscribe();

Parents = parents;
(Parents as INotifyCollectionChanged).CollectionChanged += MainWindow_CollectionChanged;

Button click codes:

private void AddADataButton_Click(object sender, RoutedEventArgs e)
{
    var data = new Person() { FirstName = "Data", LastName = "Data"};
    _parentsSource.Add(data);
}

Step to reproduce

1. Run the sample.
2. Click the “ADD” button.
3. Ensure the Action property value shown in the MessageBox [i.e., “Reset”].
4. Again click the “ADD” button.
5. Ensure the Action property value shown in the MessageBox [i.e.,“Add”].

Reproduction repository

NA

Expected behavior

The e.Action property in the CollectionChanged event of the ReadOnlyObservableCollection should be reported as “Add” when adding an item to the SourceList.

Screenshots 🖼️

When adding the data for the first time.

When adding the data for second time.

I have attached the sample for the replication.

ReadOnlyObservableCollection_SimpleSample.zip

IDE

Visual Studio 2022

Operating system

Windows

Version

No response

Device

No response

DynamicData Version

8.1.1

Additional information ℹ️

No response