dotnet/wpf · error · ArgumentException

SR.Invalid_IInputElement

Error message

SR.Invalid_IInputElement

What it means

The static UIElement.AddHandler helper only accepts targets that are UIElement, UIElement3D, or ContentElement. When the given DependencyObject d is none of these, ArgumentException(SR.Invalid_IInputElement) is thrown with the actual type name.

Solutions

  1. Pass a UIElement, UIElement3D, or ContentElement as the target
  2. Check the target type before calling and route to the correct AddHandler overload
  3. Store handlers on a containing element if the object cannot own routed-event handlers

Example fix

// before
UIElement.AddHandler(ev, (DependencyObject)brush, handler); // throws
// after
if (d is UIElement ue) ue.AddHandler(ev, handler);
else if (d is ContentElement ce) ce.AddHandler(ev, handler);
else throw new NotSupportedException($"{d.GetType()} cannot own routed event handlers");
Defensive patterns

Strategy: validation

Validate before calling

if (!(d is UIElement || d is UIElement3D || d is ContentElement))
    throw new ArgumentException($"{d.GetType()} cannot own routed-event handlers");

Type guard

static bool CanAddHandlers(DependencyObject d) => d is UIElement || d is UIElement3D || d is ContentElement;

Try / catch

try { UIElement.AddHandler(ev, d, handler); }
catch (ArgumentException ex) when (ex.Message.Contains("IInputElement")) { log.Warn($"Cannot attach handler to {d?.GetType()}", ex); }

Prevention

When it happens

Trigger: Calling UIElement.AddHandler(routedEvent, d, handler) with a DependencyObject that is not an event-capable element (e.g. a raw DependencyObject, Freezable, or other non-IInputElement).

Common situations: Generic helper code written against DependencyObject instead of UIElement/ContentElement; wiring handlers on non-element objects like brushes or animations; refactors that widened parameter 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/0d9a657678bb39a8. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/UIElement.cs:1901

                uiElement.AddHandler(routedEvent, handler);
            }
            else
            {
                ContentElement contentElement = d as ContentElement;
                if (contentElement != null)
                {
                    contentElement.AddHandler(routedEvent, handler);
                }
                else
                {
                    UIElement3D uiElement3D = d as UIElement3D;
                    if (uiElement3D != null)
                    {
                        uiElement3D.AddHandler(routedEvent, handler);
                    }
                    else
                    {
                        throw new ArgumentException(SR.Format(SR.Invalid_IInputElement, d.GetType()));
                    }
                }
            }
        }

        /// <summary>
        ///     Removes a handler for the given attached event
        /// </summary>
        internal static void RemoveHandler(DependencyObject d, RoutedEvent routedEvent, Delegate handler)
        {
            ArgumentNullException.ThrowIfNull(d);

            Debug.Assert(routedEvent != null, "RoutedEvent must not be null");

            UIElement uiElement = d as UIElement;
            if (uiElement != null)
            {
                uiElement.RemoveHandler(routedEvent, handler);

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