stride3d/stride · error · NotSupportedException

NotSupportedException

Error message

NotSupportedException

What it means

UIBaseViewModel.ResolveInsertionIndex computes where to insert a UI element. If the visual parent is neither an IContentControl-like host nor a Panel (e.g. it is a ContentPresenter, Border, or other non-Panel container that exposes no children collection), no index can be resolved and it throws NotSupportedException. This is a deliberate fail-fast for unsupported visual-tree parents.

Solutions

1. Wrap the insertion target in a Panel-derived container (Grid/StackPanel) so the parent resolves as Panel.
2. Insert the element before it is wrapped, or target the actual Panel inside the template via FindAncestor/FindName.
3. Ensure the element is added to the visual tree (loaded) before calling InsertUIElement so parent is final.
4. If you own a custom container, derive it from Panel to gain Children-based insertion support.

Example fix

// before
viewModel.InsertUIElement(myControl, borderHost, index); // Border is not a Panel
// after
var grid = new Grid();
grid.Children.Add(myControl);
borderHost.Child = grid;
viewModel.InsertUIElement(myControl, grid, index);

if (!(parent is Panel) && !(parent is IContentControl))
    throw new InvalidOperationException($"Parent {parent.GetType().Name} is not a supported insertion container");
viewModel.InsertUIElement(element, parent, index);

bool IsInsertableContainer(object o) => o is Panel || o is IContentControl;

When it happens

Trigger: Calling InsertUIElement (or InsertUIElementBefore/After) with a parent element whose XAML visual parent is not a Panel (not Grid/StackPanel/Canvas/etc.) and not a supported content control, or while the element is not yet attached to the visual tree so parent resolution lands on an unsupported type.

Common situations: Inserting a control inside a Border or ContentControl wrapper; inserting while the target container is still in a template (ContentPresenter); calling before the view is loaded so parent is a transitional visual type; custom panels that don't derive from Panel.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Unable to reach the ItemsPresenter of the associated…
• Unable to reach the VirtualizingTilePanel of the associated…
• The given window does not contain a ContentPresenter.
• Value cannot be null. (Parameter 'getChildrenCountFunc')
• Value cannot be null. (Parameter 'getChildFunc')

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/4677d5727803efd6. Report an issue: GitHub.

Appendix: source

Thrown at sources/editor/Stride.Assets.Presentation/ViewModel/UIBaseViewModel.cs:77

        /// <returns>The index in which to insert a child.</returns>
        private int ResolveInsertionIndex(UIElement parent, int index)
        {
            if (parent == null)
            {
                return index >= 0 ? index : Asset.Hierarchy.RootParts.Count;
            }

            var control = parent as ContentControl;
            if (control != null)
            {
                return index >= 0 ? index : 0;
            }
            var panel = parent as Panel;
            if (panel != null)
            {
                return index >= 0 ? index : panel.Children.Count;
            }
            throw new NotSupportedException();
        }
    }
}

View on GitHub (pinned to 96fad776d2)