InvalidOperationException when SelectedItem changes in ObservableCollection

[alexandrehtrb]

Describe the bug

Avalonia 11.3.11
.NET 10
Windows 11 23H2 x64

I am running some UI tests and this bug shows up on Visual Studio. It doesn't crash the app, but this wasn't happening with the previous Avalonia version (11.0.5).
Seems related to SelectedItem and SelectedItems binding in a TreeView.
When I remove an item from an ObservableCollection bound to a TreeView, this Exception arises:

System.InvalidOperationException: 'Cannot change ObservableCollection during a CollectionChanged event.'

XAML:

<TreeView
    x:Name="itemsTree"
    Margin="0 40 0 20"
    ItemsSource="{Binding Items}"
    SelectedItem="{Binding CollectionGroupSelectedItem, Mode=TwoWay}"
    SelectedItems="{Binding CollectionGroupSelectedItems, Mode=TwoWay}"
    SelectionMode="Multiple"
    ScrollViewer.HorizontalScrollBarVisibility="Disabled"
    Classes="sidebar DragAndDrop CollectionOrganizationItemDragAndDrop">

ViewModel:

public override ObservableCollection<CollectionViewModel> Items { get; }

public ObservableCollection<CollectionOrganizationItemViewModel> CollectionGroupSelectedItems { get; }

private CollectionOrganizationItemViewModel? collectionGroupSelectedItemField;
public CollectionOrganizationItemViewModel? CollectionGroupSelectedItem
{
    get => this.collectionGroupSelectedItemField;
    set
    {
        this.RaiseAndSetIfChanged(ref this.collectionGroupSelectedItemField, value);
        this.onCollectionsGroupItemSelected(this.collectionGroupSelectedItemField);
    }
}

private readonly Action<CollectionOrganizationItemViewModel?> onCollectionsGroupItemSelected;

To Reproduce

Expected behavior

No response

Avalonia version

11.3.11

OS

Windows

Additional context

No response

[timunie]

Happens typically if called from wrong thread. Please provide a full minimum sample

[alexandrehtrb]

Reproduction steps:

1. Clone repo on branch net10migration
2. Run Pororoca.Desktop project
3. On the top menu, Help > Run UI tests (Ctrl+F12)
4. Click on None and select only TreeDeleteItemsUITest
5. Run tests
6. Exception should appear on Visual Studio

[timunie]

This is not really a minimal sample for investigation. you could build avalonia from source and add it as a project reference, then you may be able to get a break point at where it actually fails 🤔

[alexandrehtrb]

After executing this line:

public void DeleteSubItem(CollectionOrganizationItemViewModel item)
{
    CollectionsGroupViewDataCtx.Items.Remove((CollectionViewModel)item); // here
    ...
}

Visual Studio captures an Exception on the SelectedItem.set property binding, shown on the picture above.

There shouldn't be a problem regarding threads, because the UI tests code runs on the UI thread, via

Dispatcher.UIThread.Post(async () => await RunTestsAsync());

😕

[alexandrehtrb]

To be more specific, this Exception happens when a TreeViewItem is being deleted and both it and a descendant are selected, example:

TreeView

• tvi1
• tvi2
  • tvi2_1
  • tvi2_2

tvi2 and tvi2_2 are selected and tvi2 is being deleted.