[TreeView] weird selection behavior when I try to remove an item

[YkTru]

Hi, I'm working on a TreeView with an attached SelectedItem property to handle all common tree view operations.

[Expected Behavior]: When removing a selected item:

• If it has a previous sibling, select that.
• Otherwise, if it's the first item, select the next sibling.
• If no siblings exist, select nothing.

[Problem]: Everything works as expected, except when I remove an item. Sometimes, the selection briefly selects the parent before settling on the previous item:

Video_2025-01-30_144213.mp4

[Intended Flow]:
Select item X → Store previous sibling Y → Remove item X → Select Y

[Actual Behavior]:
Select item X → Store previous sibling Y → Remove item X → ?? Select parent ?? → Select Y

[Bonus Questions]:

1. Is my approach of using an attached property idiomatic/best practice?
2. I plan to refactor my model from class to record—could this introduce any unexpected issues?

Thanks!

[edit]: Here's my repo

[miloush]

Were you meant to attach or link a project?

[YkTru]

Sorry I forgot to put the link to my repo!

https://github.com/YkTru/TreeView_exploration/tree/master/Deselection_Issue

(also the project should be more appropriately named "Selection_Issue")

[YkTru]

@miloush

I think the problem might be in the Attached Prop with PerformSelection and/or OnSelectedItemChanged what do you think?

The RemoveSelectedItem looks right to me

I've tried to "hack" some stuff by adding delay and changing highlighted selected item's brush (temporarily) to transparent but I hate these approaches.

Otherwise I hope the problem is not with WPF TreeView (?)

[miloush]

By default if you remove a selected item, the TreeView selects the first item:

wpf/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/TreeView.cs

Lines 415 to 420 in b1d86ae

	case NotifyCollectionChangedAction.Remove:
	case NotifyCollectionChangedAction.Reset:
	if ((SelectedItem != null) && !IsSelectedContainerHookedUp)
	{
	SelectFirstItem();
	}

To avoid this, you should select a new item first and then remove the one you want to remove.

[YkTru]

To avoid this, you should select a new item first and then remove the one you want to remove.

Here's what I tried:

[RelayCommand(CanExecute = nameof(CanRemoveSelectedItem))]
private void RemoveSelectedItem()
{
    var selected = SelectedItem;

    if (selected is null)
        return;

    var siblings = selected.Parent?.Children ?? HierarchicalItems;

    var index = siblings.IndexOf(selected);

    if (index < 0)
        return;

    SelectedItem = siblings.ElementAtOrDefault(index + 1) ?? siblings.ElementAtOrDefault(index - 1);

    siblings.RemoveAt(index);

    RefreshCanExecute(); // changes nothing if commented out
}

Here's what happen:

Video_2025-02-01_190209.mp4

What would you do? I'm out of idea honnestly (I've tried a lot of stuff, and the only thing that almost worked was adding delay + changing highlight brush to transparent before it selects parent -> this is unacceptable since it necessarily adds "lag" to the user experience).

[miloush]

Selecting the first item is a reasonable thing to do. There are really only two options, either leave it with nothing selected, or select an easily accessible item. The TreeView cannot traverse the tree looking for what would be the closest item to select instead, there is unknown items of unknown depths (possibly infinite). You, however, know the data, and in some cases that means you can easily tell which is a better item to select. You can override the default behavior by inheriting your own control from the TreeView and overriding the method.

Or, as suggested, you select it first and then remove an unselected item. The reason why it keeps jumping is because you schedule SelectTreeViewItem with an outdated item for when the dispatcher is not busy. If you call it directly in PerformSelection, e.g. treeView.Dispatcher.Invoke(selectAction); it will stop jumping.

[YkTru]

@miloush It works! Thank you so much for your guidance. Those "little" bug can drive crazy sometimes! I also had some help with gpt feeding it with our discussions.

Video_2025-02-01_214221.mp4

[Solution]: I made a custom treeview where I override OnItemsChanged:

public class CustomTreeView : TreeView
{
        // (...)
        protected override bool IsItemItsOwnContainerOverride(object item)
        {
            return item is CustomTreeViewItem;
        }

        protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)
        {
            if (e.Action == NotifyCollectionChangedAction.Remove ||
                e.Action == NotifyCollectionChangedAction.Reset)
            {
                // Do nothing: we are controlling selection via our view-model command.
                return;
            }
            base.OnItemsChanged(e);
        }
}

And for children:

public class CustomTreeViewItem : TreeViewItem
{
    protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Remove ||
            e.Action == NotifyCollectionChangedAction.Reset)
        {
            // Do nothing: bypass auto-selecting a sibling/parent.
            return;
        }
        base.OnItemsChanged(e);
    }