dotnet/wpf · error · InvalidOperationException

SR.Format(SR.Invalid_IInputElement, relativeTo.GetType())

Error message

SR.Format(SR.Invalid_IInputElement, relativeTo.GetType())

What it means

MouseDevice.GetPosition throws InvalidOperationException with SR.Invalid_IInputElement when the relativeTo argument is non-null but is not a valid input element (UIElement, ContentElement, or UIElement3D). The mouse position must be reported relative to an element that can receive input. WPF validates the reference element's type before computing coordinates.

Solutions

  1. Call Mouse.GetPosition on the hosting UIElement or the Window instead of the raw Visual
  2. Convert coordinates afterwards with TransformToVisual if you need them relative to a non-input Visual
  3. Guard with InputElement.IsValid(relativeTo) before calling

Example fix

// before
Point p = Mouse.GetPosition(myDrawingVisual); // throws
// after
Point pH = Mouse.GetPosition(hostControl);          // hostControl is UIElement
Point p = hostControl.TransformToVisual(myDrawingVisual).Transform(pH);
Defensive patterns

Strategy: validation

Validate before calling

if (relativeTo != null && !InputElement.IsValid(relativeTo))
    throw new InvalidOperationException("relativeTo must be UIElement, ContentElement, or UIElement3D");

Type guard

static bool IsValidMouseRelative(object o) =>
    o == null || o is UIElement || o is ContentElement || o is UIElement3D;

Try / catch

try { var p = Mouse.GetPosition(relativeTo); }
catch (InvalidOperationException) { var p = Mouse.GetPosition((UIElement)hostControl); }

Prevention

When it happens

Trigger: Calling Mouse.GetPosition(someVisual) or mouse.GetPosition(relativeTo) with a plain Visual/DrawingVisual/DependencyObject that does not implement input properly.

Common situations: Requesting mouse coordinates relative to a DrawingVisual in a custom control; passing a Visual returned from VisualTreeHelper that is not a UIElement.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ff1a5cc7f2ad35b4. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/MouseDevice.cs:546

        {
            get
            {
                return GetButtonState(MouseButton.XButton2);
            }
        }

        /// <summary>
        ///     Calculates the position of the mouse relative to
        ///     a particular element.
        /// </summary>
        public Point GetPosition(IInputElement relativeTo)
        {
//             VerifyAccess();

            // Validate that relativeTo is either a UIElement, a ContentElement or a UIElement3D.
            if (relativeTo != null && !InputElement.IsValid(relativeTo))
            {
                throw new InvalidOperationException(SR.Format(SR.Invalid_IInputElement, relativeTo.GetType()));
            }

            PresentationSource relativePresentationSource = null;

            if (relativeTo != null)
            {
                DependencyObject dependencyObject = relativeTo as  DependencyObject;
                DependencyObject containingVisual = InputElement.GetContainingVisual(dependencyObject);

                if (containingVisual != null)
                {
                    relativePresentationSource = PresentationSource.CriticalFromVisual(containingVisual);
                }
            }
            else
            {
                if (_inputSource is not null)
                {

View on GitHub (pinned to 81131a70a4)