dotnet/wpf · error · Win32Exception

Win32Exception (native SystemParametersInfo failure…

Error message

Win32Exception (native SystemParametersInfo failure retrieving HighContrast)

What it means

The HighContrast property queries SPI_GETHIGHCONTRAST through SystemParametersInfo; on failure the cache slot is reset and a Win32Exception is thrown. It means the OS declined to report whether high-contrast mode is on. This is thrown from the public property getter on first (uncached) access.

Solutions

Retry the read - the invalidated cache slot makes the next access re-query the OS.
Catch Win32Exception and assume high contrast is off (or ask the user) as a fallback.
Ensure the code runs in an interactive user session with access to the default desktop.
Check environment policy (remote session restrictions, AppLocker/service account) if failures are persistent.

Example fix

// before
bool hc = SystemParameters.HighContrast;
// after
bool hc;
try { hc = SystemParameters.HighContrast; }
catch (Win32Exception) { hc = false; }

Defensive patterns

Strategy: try-catch

Validate before calling

bool sessionOk = !SystemInformation.TerminalServerSession && Environment.UserInteractive;
// only read SystemParameters.HighContrast when sessionOk, else assume false

Try / catch

bool hc;
try { hc = SystemParameters.HighContrast; }
catch (Win32Exception ex)
{
    Trace.TraceWarning($"HighContrast SPI failed: {ex.NativeErrorCode}");
    hc = false;
}

Prevention

Retry once - the invalidated cache slot re-queries the OS
Default to 'high contrast off' when the query fails
Query on the UI thread of an interactive session
Handle SystemParameters.StaticPropertyChanged instead of polling where possible

When it happens

Trigger: Reading SystemParameters.HighContrast when the native SystemParametersInfo(SPI_GETHIGHCONTRAST) call returns false, e.g. no interactive window station, restricted tokens, or an accessibility-API failure in remoted sessions.

Common situations: Accessibility-aware apps checking high-contrast at startup from a service; terminal-server sessions with restricted UI access; security-hardened environments blocking SPI queries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/2303290238f9405d. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/SystemParameters.cs:179

            {
                lock (_cacheValid)
                {
                    while (!_cacheValid[(int)CacheSlot.HighContrast])
                    {
                        _cacheValid[(int)CacheSlot.HighContrast] = true;

                        NativeMethods.HIGHCONTRAST_I highContrast = new NativeMethods.HIGHCONTRAST_I
                        {
                            cbSize = Marshal.SizeOf(typeof(NativeMethods.HIGHCONTRAST_I))
                        };
                        if (UnsafeNativeMethods.SystemParametersInfo(NativeMethods.SPI_GETHIGHCONTRAST, highContrast.cbSize, ref highContrast, 0))
                        {
                            _highContrast = (highContrast.dwFlags & NativeMethods.HCF_HIGHCONTRASTON) == NativeMethods.HCF_HIGHCONTRASTON;
                        }
                        else
                        {
                            _cacheValid[(int)CacheSlot.HighContrast] = false;
                            throw new Win32Exception();
                        }
                    }
                }

                return _highContrast;
            }
        }

        /// <summary>
        /// Maps to SPI_GETMOUSEVANISH.
        /// </summary>
        // If this becomes public, it will need a matching ResourceKey.
        internal static bool MouseVanish
        {
            get
            {
                lock (_cacheValid)
                {

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