dotnet/wpf · error · InvalidEnumArgumentException

InvalidEnumArgumentException("options", (int)options…

Error message

InvalidEnumArgumentException("options", (int)options, typeof(MessageBoxOptions))

What it means

MessageBox.ShowCore validates that options is a defined MessageBoxOptions value or a valid combination of its flags. An undefined value or combination raises InvalidEnumArgumentException naming parameter "options" and type MessageBoxOptions.

Solutions

Pass only MessageBoxOptions-defined flags: DefaultDesktopOnly, RightAlign, RtlReading, ServiceNotification (or a valid combination of these).
Mask/validate stored ints against the enum's defined flags before passing, e.g. Enum.IsDefined or a flags-range check.
Avoid raw Win32 constants; map them explicitly to MessageBoxOptions members.

Example fix

// before
var opt = (MessageBoxOptions)win32Flags; // arbitrary Win32 bits
MessageBox.Show(msg, title, MessageBoxButton.OK, MessageBoxImage.None, MessageBoxResult.OK, opt);
// after
var opt = MessageBoxOptions.None;
if ((win32Flags & 0x80000) != 0) opt |= MessageBoxOptions.RightAlign;
if ((win32Flags & 0x100000) != 0) opt |= MessageBoxOptions.RtlReading;
MessageBox.Show(msg, title, MessageBoxButton.OK, MessageBoxImage.None, MessageBoxResult.OK, opt);

Defensive patterns

Strategy: validation

Validate before calling

const MessageBoxOptions ValidFlags = MessageBoxOptions.DefaultDesktopOnly | MessageBoxOptions.RightAlign | MessageBoxOptions.RtlReading | MessageBoxOptions.ServiceNotification;
bool valid = (options & ~ValidFlags) == 0;
if (!valid) options = MessageBoxOptions.None;

Type guard

bool IsValidOptions(MessageBoxOptions o) => (o & ~(MessageBoxOptions.DefaultDesktopOnly | MessageBoxOptions.RightAlign | MessageBoxOptions.RtlReading | MessageBoxOptions.ServiceNotification)) == 0;

Try / catch

try { MessageBox.Show(msg, title, button, icon, result, options); }
catch (InvalidEnumArgumentException ex) when (ex.ParamName == "options") { MessageBox.Show(msg, title, button, icon, result, MessageBoxOptions.None); }

Prevention

Build options from named flags, never from raw Win32 ints
Mask stored flag ints against the enum's defined bits
Remember only these four flags exist: DefaultDesktopOnly, RightAlign, RtlReading, ServiceNotification

When it happens

Trigger: Calling MessageBox.Show with an options argument that is not a valid MessageBoxOptions (RightAlign, RtlReading, DefaultDesktopOnly, ServiceNotification) combination, e.g. (MessageBoxOptions)0x400 from raw Win32 flags.

Common situations: Porting Win32 MessageBox flag constants directly; combining options bitwise with unrelated flags; building options from stored int settings.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/31678170c83af158. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/MessageBox.cs:384

            MessageBoxImage icon,
            MessageBoxResult defaultResult,
            MessageBoxOptions options)
        {
            if (!IsValidMessageBoxButton(button))
            {
                throw new InvalidEnumArgumentException ("button", (int)button, typeof(MessageBoxButton));
            }
            if (!IsValidMessageBoxImage(icon))
            {
                throw new InvalidEnumArgumentException ("icon", (int)icon, typeof(MessageBoxImage));
            }
            if (!IsValidMessageBoxResult(defaultResult))
            {
                throw new InvalidEnumArgumentException ("defaultResult", (int)defaultResult, typeof(MessageBoxResult));
            }
            if (!IsValidMessageBoxOptions(options))
            {
                throw new InvalidEnumArgumentException("options", (int)options, typeof(MessageBoxOptions));
            }

            // UserInteractive??
            //
            /*if (!SystemInformation.UserInteractive && (options & (MessageBoxOptions.ServiceNotification | MessageBoxOptions.DefaultDesktopOnly)) == 0) {
                throw new InvalidOperationException("UNDONE: SR.GetString(SR.CantShowModalOnNonInteractive)");
            }*/

            if ( (options & (MessageBoxOptions.ServiceNotification | MessageBoxOptions.DefaultDesktopOnly)) != 0)
            {
                if (owner != IntPtr.Zero)
                {
                    throw new ArgumentException(SR.CantShowMBServiceWithOwner);
                }
            }
            else
            {
                if (owner == IntPtr.Zero)

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