The selected node of TreeView will be automatic change when expand

[zhuxb711]

Describe the bug

The selected item in TreeView will be automatic change when expand
Steps to reproduce the bug

Steps to reproduce the behavior:

1. Select a node in TreeView, which is not expanded
2. Then expand this node, now the selected node of treeview was changed to its sub node.

Expected behavior

The selected node of TreeView should not be changed
Screenshots

Version Info

NuGet package version:

2.3.191211002

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
May 2019 Update (18362)	Yes
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Mobile
Xbox
Surface Hub
IoT

Additional context

[kmahone]

@zhuxb711, thanks for reporting this issue. I was not able to reproduce the issue myself. Could you please share a repro app with us?

Could you also please clarify how you are interacting with the TreeView? Are you using mouse or keyboard?

Thanks.

[zhuxb711]

@kmahone I'm using mouse to interact.

I make a demo for you, this problem does exist. &If I select parent node and then expand it, the selection will be changed to its subnode.

Tips: Before you run the demo, please granting "file system access" in system setting for demo
TreeViewTest.zip

[kmahone]

Thanks @zhuxb711 I can reproduce the issue now.

[kmahone]

@kaiguo can you please take a look to determine the root cause here and come up with a workaround if possible.

[zhuxb711]

@kmahone This problem is very confusing to my users and hopes to be fixed as soon as possible

[zhuxb711]

I want to know when this problem can be fixed @kmahone

[ranjeshj]

@zhub711 there have been some fixes to TreeView, can you see if the issue repros in the latest prerelease (went out today). @kaiguo did you get a chance to look at this ?

[zhuxb711]

I have installed the latest preview version and tested this issue, it still exists and has not been fixed @ranjeshj

[ranjeshj]

This is really weird behavior. I'm not sure yet why the expansion and populating of the children collection would affect the selection state. @zhuxb711 One hacky workaround to unblock you could be to save and restore the selection after the expand operation like so.

var oldSelectedNode = FolderTree.SelectedNode;
if (args.Node.HasUnrealizedChildren)
{
await FillTreeNode(args.Node);
}
FolderTree.SelectedNode = oldSelectedNode;

[zhuxb711]

@ranjeshj @kaiguo But this code still looks strange. I also think that expanding a selected TreeViewNode will cause the selected item to change very strangely. Is there any progress in the investigation of the cause of this problem?

[kaiguo]

@ranjeshj not 100% sure but it probably has something to do with this,

microsoft-ui-xaml/dev/TreeView/TreeViewList.cpp

Lines 356 to 359 in ca95be6

	if (selectionState != itemNode->SelectionState())
	{
	ListViewModel()->UpdateSelection(*itemNode, selectionState);
	}

I think this code was added to reverse some ListView selection changes we didn't want when using databinding. The demo code works on TreeNode directly and doesn't use ItemsSource binding. Perhaps we should execute the code block above only in content mode so adding an extra IsContentMode() check might fix the issue.

[Felix-Dev]

@kaiguo You probably should test it yourself but I went ahead and added your suggestion to the TreeViewList, then built a nuget package of WinUI and used it on the repro app. Result: I'm still seeing the same erroneous selection change behavior reported here.

[zhuxb711]

@kaiguo @ranjeshj
I see other people asking the same question. Is there any progress in the investigation of this issue?

[ranjeshj]

@chingucoding Thanks for the PR. @StephenLPeters can you please review this PR ? Thanks!