TreeView control will cause app to hang when using virtualization + an item in ItemsSource is null

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

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[severity:It's more difficult to complete my work]
Found this issue after upgrading a project from .Net Framework 4.8 to .NET 8. It seems there has been a change maybe from prior versions to how virtualization works.

I have a TreeView that gets bound to a list, and found that an app (dispatcher) hang will occur under the specific conditions that:

1: At least one item in the ItemsSource collection is null
2: The VirtualizingPanel.IsVirtualizing="true" property is set on the TreeView
3: The default style for the ItemContainerStyle specifies that IsExpanded is true

If these conditions are met, the app dispatcher will become flooded with calls to ArrangeOverride ie. will keep trying to rearrange the VirtualizingStackPanel for some reason, causing all user interactivity to freeze and the application to lock up.

This happens on both .NET 5 and 8 as far as I have tested this.

Please see attached documents for a sample MainWindow XAML and code-behind.

MainWindow.zip

Note that changing either the ItemContainerStyle IsExpanded, the virtualization mode or by removing any null references in the ItemsSource collection, this "bug" seems to not occur. I suspect something in how TreeViewItems get rendered means that they keep trying to reevaluate their size in this niche instance where the container has nothing to render, but at this point my knowledge of the WPF layout/virtualization system runs out.

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Original Comments

Feedback Bot on 19/9/2025, 08:57 AM:

We have directed your feedback to the appropriate engineering team for further evaluation. The team will review the feedback and notify you about the next steps.

[appstatic-dev]

A couple of questions:

1. Are you using a HierarchicalDataTemplate to add items or using TreeViewItem ?
2. How deep does the index go ?
3. How many items in total are you adding to the TreeVIew ?
4. Are you trying to manipulate items in the RequestBringIntoView EventHandler ? Just be aware that there is a RequestBringIntoView Event on the TreeView and a RequestBringIntoView Event on the TreeViewItem.

Using a VirtualizingPanel for my implementation causes all sorts problems when advance control is required. Navaigation and in particular IsExpanded is difficult to control and unexpected behavior is common. Also, what you will find is the when you want to expand a node that has its parents collapsed the UIElementCollection from GetChild of the VisualTreeHelper when passing the ItemPresenter may return null.

I injected a couple of null items into my my index in different places with the only issue being that keyboard navigation does not work when trying to selected those items. Selecting with the mouse works.

My hierarchy is 10 deep and loaded with over a thousand items and performs super fast and no thanks to me of course and we can only thank the WPF team for that.