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

RibbonApplicationMenu.GetContainerForItemOverride validates that an existing item container passed back into the menu is one of the allowed types: RibbonApplicationMenuItem, RibbonApplicationSplitMenuItem, RibbonSeparator, or RibbonGallery. Any other container type throws InvalidOperationException (InvalidApplicationMenuOrItemContainer) naming the menu type and the offending container.

Solutions

Ensure container generation produces RibbonApplicationMenuItem, RibbonApplicationSplitMenuItem, RibbonSeparator, or RibbonGallery only.
If overriding GetContainerForItemOverride/IsItemItsOwnContainerOverride in a subclass, restrict accepted containers to the allowed types.
Remove explicit ItemContainerStyle/container assignments that force unsupported container types.

Example fix

// before
protected override DependencyObject GetContainerForItemOverride()
{
    return new MenuItem(); // unsupported
}
// after
protected override DependencyObject GetContainerForItemOverride()
{
    return new RibbonApplicationMenuItem();
}

Defensive patterns

Strategy: type-guard

Validate before calling

bool ok = obj is RibbonApplicationMenuItem || obj is RibbonApplicationSplitMenuItem || obj is RibbonSeparator || obj is RibbonGallery;

Type guard

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

Try / catch

try { return GetContainerForItemOverride(); }
catch (InvalidOperationException ex) when (ex.Message.Contains("container")) { return new RibbonApplicationMenuItem(); }

Prevention

Override IsItemItsOwnContainerOverride to accept only the four allowed types.
Return RibbonApplicationMenuItem (or SplitMenuItem) from GetContainerForItemOverride overrides.
Keep ItemContainerStyle aligned with Ribbon container types.

When it happens

Trigger: Providing an item container of the wrong type — e.g. returning a custom Button/MenuItem from GetContainerForItemOverride in a derived RibbonApplicationMenu, or binding items whose explicit ItemContainerStyle/type maps to an unsupported container.

Common situations: Subclassing RibbonApplicationMenu and overriding container generation, or ItemsSource items with ItemContainerStyle set to non-ribbon containers; template/style retargeting that swaps container types.

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/ce6f9466daf4246b. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Windows.Controls.Ribbon/Microsoft/Windows/Controls/Ribbon/RibbonApplicationMenu.cs:241

        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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