dotnet/wpf · error · Win32Exception

Win32Exception (native SystemParametersInfo failure…

Error message

Win32Exception (native SystemParametersInfo failure retrieving DropShadow)

What it means

The DropShadow property queries SPI_GETDROPSHADOW via SystemParametersInfo; failure invalidates the cache slot and throws Win32Exception. It means the OS would not report whether menu/tool window drop shadows are enabled. Raised by the public getter on first access.

Solutions

Enable the Themes service / visual styles on the machine, then retry.
Catch Win32Exception and default to false (shadows off).
Retry the read - the next access re-queries the OS because the cache was invalidated.
Gate the read on environment checks (TerminalServerSession, theme support) and skip on hostile environments.

Example fix

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

Defensive patterns

Strategy: try-catch

Validate before calling

bool themesRunning = SystemParameters.ClientAreaAnimation is bool _; // probe cheap system params
// or check service state of 'Themes' before reading DropShadow

Try / catch

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

Prevention

Ensure the Themes service runs on target machines
Retry once - the next read re-issues the SPI call
Default to false (shadows off) on failure
Validate visual styles availability in deployment checks

When it happens

Trigger: Reading SystemParameters.DropShadow when SystemParametersInfo(SPI_GETDROPSHADOW) returns false, e.g. themes disabled or unsupported on the host (server SKUs, remote sessions with visual styles off).

Common situations: Apps capturing UI settings at startup on servers without the Themes service; remote sessions with 'show window contents while dragging'/visual effects disabled; custom minimal OS images.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/918b682ac5edd5b2. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/SystemParameters.cs:298

        ///     Maps to SPI_GETDROPSHADOW
        /// </summary>
        public static bool DropShadow
        {
            get
            {
                lock (_cacheValid)
                {
                    while (!_cacheValid[(int)CacheSlot.DropShadow])
                    {
                        _cacheValid[(int)CacheSlot.DropShadow] = true;

                        if (UnsafeNativeMethods.SystemParametersInfo(NativeMethods.SPI_GETDROPSHADOW, 0, ref _dropShadow, 0))
                        {
                        }
                        else
                        {
                            _cacheValid[(int)CacheSlot.DropShadow] = false;
                            throw new Win32Exception();
                        }
                    }
                }

                return _dropShadow;
            }
        }

        /// <summary>
        ///     Maps to SPI_GETFLATMENU
        /// </summary>
        public static bool FlatMenu
        {

            get
            {
                lock (_cacheValid)
                {

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