What causes "SR.Stylus_PenContextFailure" in dotnet/wpf?

Ensure the window (HwndSource) is fully created — handle non-zero — before stylus contexts initialize

dotnet/wpf · error · InvalidOperationException

SR.Stylus_PenContextFailure

Error message

SR.Stylus_PenContextFailure

What it means

PenContexts binds wisp (legacy) stylus input to a specific HWND. Its constructor throws InvalidOperationException (SR.Stylus_PenContextFailure) when the PresentationSource is not an HwndSource or the HwndSource handle is IntPtr.Zero, because pen contexts can only be created for a live HWND-backed window.

Solutions

Ensure the window (HwndSource) is fully created — handle non-zero — before stylus contexts initialize
Check PresentationSource.FromVisual(elem) is an HwndSource with a valid handle before touching PenContexts
Do not dispose the HwndSource while stylus input is active
Verify the code path is on a standard Window/Page hosting (HWND-based) environment

Example fix

// before
var ctx = new PenContexts(logic, PresentationSource.FromVisual(myVisual));
// after
var src = PresentationSource.FromVisual(myVisual) as HwndSource;
if (src == null || src.Handle == IntPtr.Zero) return;
var ctx = new PenContexts(logic, src);

Defensive patterns

Strategy: validation

Validate before calling

var src = PresentationSource.FromVisual(visual) as HwndSource;
if (src == null || src.Handle == IntPtr.Zero)
    return; // cannot initialize pen contexts

Type guard

bool IsValidHwndSource(PresentationSource s) => s is HwndSource hs && hs.Handle != IntPtr.Zero;

Try / catch

try { new PenContexts(logic, src); }
catch (InvalidOperationException ex) { Log.Error("PenContexts requires live HwndSource", ex); }

Prevention

Only initialize stylus after the window handle exists
Do not use fake PresentationSource subclasses in tests
Disable stylus support before closing the HwndSource

When it happens

Trigger: Constructing PenContexts directly with a PresentationSource that is not HwndSource (e.g. a custom PopupSource/test double), or with an HwndSource whose window handle is zero (window not yet created or already disposed).

Common situations: Creating stylus input before the window is shown/initialized; accessing PenContexts after window close; running in environments without HWND-backed presentation (custom presentation sources); unit tests substituting a fake PresentationSource.

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/bd5d2218f9d87fe9. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Stylus/Wisp/PenContexts.cs:18

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Windows.Input.StylusWisp;
using System.Windows.Media;
using System.Windows.Input.StylusPlugIns;
using System.Windows.Interop;

namespace System.Windows.Input
{
    internal sealed class PenContexts
    {
        internal PenContexts(WispLogic stylusLogic, PresentationSource inputSource)
        {
            HwndSource hwndSource = inputSource as HwndSource;
            if(hwndSource == null || IntPtr.Zero == (hwndSource).Handle)
            {
                throw new InvalidOperationException(SR.Stylus_PenContextFailure);
            }

            _stylusLogic = stylusLogic;
            _inputSource = hwndSource;
        }

        /////////////////////////////////////////////////////////////////////////

        internal void Enable()
        {
            if (_contexts == null)
            {
                // create contexts
                _contexts = _stylusLogic.WispTabletDevices.CreateContexts(_inputSource.Handle, this);

                foreach(PenContext context in _contexts)
                {
                    context.Enable();

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