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

RibbonApplicationSplitMenuItem.GetContainerForItemOverride is called by the WPF ItemsControl machinery when it needs a container for an item. If an existing container is supplied (e.g. via ItemContainerStyle or direct Items.Add), it must be a RibbonApplicationMenuItem, RibbonApplicationSplitMenuItem, RibbonSeparator, or RibbonGallery; anything else makes the RibbonApplicationSplitItem menu unable to host it, so an InvalidOperationException is thrown naming the menu type and the offending container.

Solutions

Use only RibbonApplicationMenuItem, RibbonApplicationSplitMenuItem, RibbonSeparator, or RibbonGallery as direct children of the application menu / split menu item.
If databinding, set ItemContainerStyle targeting the correct container type (or use ItemTemplate so items are rendered inside a valid container) instead of letting foreign containers be produced.
If you need different content, wrap it in a valid container's Content/ItemsSource rather than adding it as a raw item.
Catch InvalidOperationException around container generation only if you are intentionally probing unsupported containers; prefer fixing the item types.

Example fix

// before
<ribbon:RibbonApplicationSplitMenuItem ItemsSource="{Binding Tools}" /> <!-- Tools are plain objects, wrong container -->

// after
<ribbon:RibbonApplicationSplitMenuItem ItemsSource="{Binding Tools}">
  <ribbon:RibbonApplicationSplitMenuItem.ItemContainerStyle>
    <Style TargetType="ribbon:RibbonApplicationMenuItem" />
  </ribbon:RibbonApplicationSplitMenuItem.ItemContainerStyle>
</ribbon:RibbonApplicationSplitMenuItem>

Defensive patterns

Strategy: validation

Validate before calling

bool IsValidAppMenuContainer(object item) =>
    item is RibbonApplicationMenuItem || item is RibbonApplicationSplitMenuItem ||
    item is RibbonSeparator || item is RibbonGallery;

Type guard

bool IsValidAppMenuContainer(object item) => item is DependencyObject d && (d is RibbonApplicationMenuItem || d is RibbonApplicationSplitMenuItem || d is RibbonSeparator || d is RibbonGallery);

Prevention

Restrict direct children of RibbonApplicationSplitMenuItem to the four supported container types.
Always set ItemContainerStyle with the correct ribbon TargetType when databinding.
Don't copy plain Menu/ContextMenu XAML into the Ribbon application menu without converting container types.

When it happens

Trigger: Adding an object that is not one of the four allowed container types directly to a RibbonApplicationSplitMenuItem's Items collection, or binding ItemsSource to a collection and setting ItemContainerStyle so a foreign container type (e.g. RibbonButton, MenuItem, TextBlock) is generated/passed as itemContainer.

Common situations: Developers reusing XAML from a regular Menu/MenuItem inside the Ribbon ApplicationMenu, databinding an arbitrary business-object collection without an appropriate ItemContainerStyle, or nesting Ribbon controls of the wrong kind inside RibbonApplicationSplitMenuItem.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/e40acfee8e881be4. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Windows.Controls.Ribbon/Microsoft/Windows/Controls/Ribbon/RibbonApplicationSplitMenuItem.cs:73

        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);

View on GitHub (pinned to 81131a70a4)