dotnet/wpf · error · InvalidOperationException

Microsoft.Windows.Controls.SR.Format(Microsoft.Windows.Contr…

Error message

Microsoft.Windows.Controls.SR.Format(Microsoft.Windows.Controls.SR.InvalidApplicationMenuOrItemContainer, this.GetType().Name, itemContainer)

What it means

RibbonApplicationMenuItem.GetContainerForItemOverride (shared validation used by the application-menu item hierarchy) only accepts existing containers of type RibbonApplicationMenuItem, RibbonApplicationSplitMenuItem, RibbonSeparator, or RibbonGallery; anything else throws InvalidOperationException (InvalidApplicationMenuOrItemContainer) with the type name and container. This keeps the ribbon application menu's item hierarchy homogeneous.

Solutions

Use only RibbonApplicationMenuItem, RibbonApplicationSplitMenuItem, RibbonSeparator, or RibbonGallery as children/containers.
In subclass overrides of IsItemItsOwnContainerOverride, return false for unsupported types so the default container is generated.
Replace plain MenuItems/Buttons inside the ribbon application menu with Ribbon* equivalents.

Example fix

// before
menu.Items.Add(new MenuItem { Header = "Open" });
// after
menu.Items.Add(new RibbonApplicationMenuItem { Header = "Open" });

Defensive patterns

Strategy: type-guard

Validate before calling

if (!(child is RibbonApplicationMenuItem || child is RibbonApplicationSplitMenuItem || child is RibbonSeparator || child is RibbonGallery)) child = new RibbonApplicationMenuItem();

Type guard

static bool IsRibbonAppMenuContainer(object c) => c is RibbonApplicationMenuItem || c is RibbonApplicationSplitMenuItem || c is RibbonSeparator || c is RibbonGallery;

Try / catch

try { items.Add(child); }
catch (InvalidOperationException ex) when (ex.Message.Contains("container")) { items.Add(new RibbonApplicationMenuItem { DataContext = child }); }

Prevention

Add only Ribbon* items inside the ribbon application menu.
Convert existing MenuItem/ Button children to RibbonApplicationMenuItem.
In subclasses, never return foreign containers from container-generation overrides.

When it happens

Trigger: Marking an arbitrary UIElement as the item container (IsItemItsOwnContainerOverride path) or overriding container generation in a derived RibbonApplicationMenuItem/RibbonApplicationSubMenu to return other containers (e.g. plain MenuItem).

Common situations: Custom ribbon menu item subclasses, styles that retemplate items into unsupported container types, or placing unsupported elements directly as children of the application menu.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/3345db15fde04712. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Windows.Controls.Ribbon/Microsoft/Windows/Controls/Ribbon/RibbonApplicationMenuItem.cs:75

        protected override DependencyObject GetContainerForItemOverride()
        {
            object currentItem = _currentItem;
            _currentItem = null;

            if (UsesItemContainerTemplate)
            {
                DataTemplate itemContainerTemplate = ItemContainerTemplateSelector.SelectTemplate(currentItem, this);
                if (itemContainerTemplate != null)
                {
                    object itemContainer = itemContainerTemplate.LoadContent();
                    if (itemContainer is RibbonApplicationMenuItem || itemContainer is RibbonApplicationSplitMenuItem || itemContainer is RibbonSeparator || itemContainer is RibbonGallery)
                    {
                        return itemContainer as DependencyObject;
                    }
                    else
                    {
                        throw new InvalidOperationException(Microsoft.Windows.Controls.SR.Format(Microsoft.Windows.Controls.SR.InvalidApplicationMenuOrItemContainer, this.GetType().Name, itemContainer));
                    }
                }
            }

            return new RibbonApplicationMenuItem();
        }

        protected override bool ShouldApplyItemContainerStyle(DependencyObject container, object item)
        {
            if (container is RibbonApplicationSplitMenuItem ||
                container is RibbonSeparator ||
                container is RibbonGallery)
            {
                return false;
            }
            else
            {
                return base.ShouldApplyItemContainerStyle(container, item);

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