TreeViewItem.IsExpanded in WindowsAppSDK 1.6/1.7/1.8 behaves inconsistently when repopulating the TreeView

[usakgb]

Describe the bug

When using TreeView's item template and setting TreeViewItem.IsExpanded to True in XAML, repopulating (clearing item and then adding new items) the tree a few times collapses all items.
When binding TreeViewItem.IsExpanded to a read-only property set to True, repopulating the tree randomly collapses/expands the items.
1.5 doesn't have this issue.

Steps to reproduce the bug

A project that demonstrates the bug: https://github.com/usakgb/WinUITreeViewBug

1. Clone and run the project.
2. Click Repopulate button a few times.

Expected behavior

All items to be expanded at all times.

Screenshots

NuGet package version

Windows App SDK 1.6.3: 1.6.241114003

Packaging type

Packaged (MSIX)

Windows version

Windows 11 version 22H2 (22621, 2022 Update)

IDE

Visual Studio 2022

Additional context

No response

[github-actions]

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Please view the issues below to see if they solve your problem, and if the issue describes your problem please consider closing this one. Thank you!

Open similar issues:

• TreeViewItem does not handle IsExpanded binding correctly (#10140), similarity score: 0.84

Closed similar issues:

• TreeViewItem doesn't always handle IsExpanded binding properly (#2112), similarity score: 0.82
• TreeView doesn't preserve the value of IsExpanded when containers in "content mode" are recycled and reused (#9549), similarity score: 0.81

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[bogdan-patraucean]

Yeah, I have the same issue..

[weitzhandler]

Same issue here in 1.7:

<TreeView>
    <TreeView.ItemTemplate>
        <DataTemplate>
            <TreeViewItem
                IsExpanded="True"
                ...

When adding new items into the tree, the elements are collapsed.

[michael-hawker]

It seems we have a lot of duplicates of this issue, I wonder which should be made champion. The original issue #2112 is the oldest, but was more about WinUI 2. And the other various ones have varying levels of details. Maybe #10140 should be the new main one?

In the meantime, I wonder if the issue has to do with parent/child loading order in OnApplyTemplate and this extra check for IsInContentMode done here:

microsoft-ui-xaml/src/controls/dev/TreeView/TreeViewItem.cpp

Lines 279 to 283 in 268e068

	if (node && IsInContentMode())
	{
	UpdateNodeIsExpandedAsync(node, IsExpanded());
	node.HasUnrealizedChildren(HasUnrealizedChildren());
	}

As the bound property probably retriggers a property changed event which then updates the state, vs. the fixed case where it's probably set by the time we get to OnApplyTemplate (if I remember my ordering correctly, it's been a bit since I've thought about one of these types of issues). IIRC the children get realized first, so then they may not have the parent reference yet? This seems like a good topic for a video... or at least something better to be called out more in the docs.

Though, I'm not sure of the purpose of IsInContentMode. For the TokenizingTextBox in the Windows Community Toolkit, we gave a reference to the parent control to the items in the PrepareContainerForItemOverride vs. walking up the logical/visual tree, but TreeView isn't an ItemsControl, so things work differently here.

Just some passing thoughts taking a quick look at the code.