Scrolling a ListBox with virtualization messes up the keyboard focus

[megazyz]

Describe the bug
Scrolling a ListBox with VirtualizationMode=Simple changes the keyboard focus to another item when the focused item gets out of view. The issue does not occur when VirtualizationMode is None.

To Reproduce
Steps to reproduce the behavior:

1. Create a new project in Visual Studio using the Avalonia MVVM Application template.
2. Add an Items property to MainWindowViewModel: public List<int> Items { get; set; } = new(Enumerable.Range(0, 1000));
3. Replace the greeting TextBlock to a ListBox in MainWindow.axaml: <ListBox Items="{Binding Items}" VirtualizationMode="Simple"/>
4. Run the application
5. Click on an item in the ListBox
6. Press Up Arrow or Down Arrow keys to make the keyboard focus adorner visible
7. Start scrolling down using the scrollbar or the mouse wheel (not the keyboard), and keep scrolling
8. Every time the focused item gets out of the viewport, a new item receives the keyboard focus.
9. Change VirtualizationMode to None to make the issue disappear

The issue is also visible in the VirtualizationDemo sample.

Expected behavior
The keyboard focus should not change while scrolling.
The virtualization code should not recycle the element having the keyboard focus.

Desktop (please complete the following information):

• OS: Windows 10
• Version: 0.10.18, 11.0.0-preview2

[megazyz]

I'm going to create a pull request to fix this

[megazyz]

Sorry, I got lost, we need an expert here.

[maxkatz6]

The keyboard focus should not change while scrolling.
The virtualization code should not recycle the element having the keyboard focus.

Not sure how possible it is.
I wonder, if it was solved in WPF or UWP. Can somebody check?

[maxkatz6]

Also, if ItemsRepeater and DataGrid have the same problem (probably have)

[megazyz]

It works in WPF.

[amwx]

I know it works in WinUI, if you have one of the WinUI control galleries, it's easy to repro.

If you inspect the Native View of Selector in UWP, you can see they have several fields specifically for holding the current focus information for the items:

And the ViewManager for ItemsRepeater holds focus info too, although I haven't tested that it works:

Avalonia/src/Avalonia.Controls/Repeater/ViewManager.cs

Line 25 in 34d24a0

private IControl? _lastFocusedElement;

[megazyz]

Checking the visual children of a ListBox using the debugger shows that WPF keeps the focused element alive in the visual tree, and does not reuse it for displaying other items.

[megazyz]

I cannot reproduce this for ItemsRepeater and DataGrid.

[megazyz]

Using ItemsRepeater in ListBox may be a possible solution, see #2594