dotnet/wpf · error · InvalidOperationException

SR.Format(SR.Invalid_IInputElement…

Error message

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

What it means

WispStylusDevice.Capture (WispStylusDevice.cs:245) throws InvalidOperationException(SR.Invalid_IInputElement) when the element passed as the stylus capture target is a DependencyObject that is not a valid IInputElement (not UIElement, ContentElement, or UIElement3D). The stylus capture API only supports those three element classes.

Solutions

Cast to / use the concrete UIElement, ContentElement, or UIElement3D instance when capturing.
Check InputElement.IsValid(element) before calling Capture.
Capture an ancestor that is a proper input element instead of the raw visual.

Example fix

// before
DependencyObject target = myVisual;
stylusDevice.Capture(target, CaptureMode.Element); // throws
// after
if (InputElement.IsValid(myVisual)) stylusDevice.Capture(myVisual, CaptureMode.Element);

Defensive patterns

Strategy: type-guard

Validate before calling

if (element != null && !InputElement.IsValid(element)) return; // abort capture on unsupported element

Type guard

static bool IsCapturable(IInputElement e) => e is UIElement || e is ContentElement || e is UIElement3D;

Try / catch

try { stylusDevice.Capture(el, mode); } catch (InvalidOperationException ex) when (ex.Message.Contains("IInputElement")) { /* find nearest supported ancestor and capture that */ }

Prevention

Type capture-target variables as UIElement rather than DependencyObject/Visual
Check InputElement.IsValid before any capture call
Capture the control, not its raw visual children

When it happens

Trigger: Calling stylusDevice.Capture(el, mode) with el being a Visual/DependencyObject (e.g. a raw Visual, Visual3D, or custom DependencyObject) rather than a supported IInputElement.

Common situations: Grabbing capture on drawing visuals or decorator children held as DependencyObject references; refactored code that widened a variable's type from UIElement to DependencyObject.

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/640b7a49dfb77fd8. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Stylus/Wisp/WispStylusDevice.cs:245

            {
                throw new System.ComponentModel.InvalidEnumArgumentException("captureMode", (int)captureMode, typeof(CaptureMode));
            }

            if (element == null)
            {
                captureMode = CaptureMode.None;
            }

            if (captureMode == CaptureMode.None)
            {
                element = null;
            }

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

            doStylusCapture?.VerifyAccess();

            bool success = false;

            // The element we are capturing to must be both enabled and visible.

            UIElement e = element as UIElement;
            if (e != null)
            {
                if (e.IsVisible || e.IsEnabled)
                {
                    success = true;
                }
            }
            else
            {

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