dotnet/wpf · error · InvalidEnumArgumentException

InvalidEnumArgumentException(nameof(value)…

Error message

InvalidEnumArgumentException(nameof(value), (int)mouseAction, typeof(MouseAction))

What it means

MouseActionConverter.ConvertTo accepts only the seven defined MouseAction values; anything else throws InvalidEnumArgumentException for 'value'. This converts the enum back to its string form for serialization/XAML output, so undefined enum values cannot be represented.

Solutions

Only pass defined MouseAction enum members (LeftClick..MiddleDoubleClick)
Validate the value against the known members before calling ConvertTo
Sanitize config data with the enum converter when loading

Example fix

// before
string s = (string)converter.ConvertTo(null, culture, (MouseAction)rawInt, typeof(string));
// after
var action = (MouseAction)rawInt;
bool defined = action is MouseAction.LeftClick or MouseAction.RightClick or MouseAction.MiddleClick
    or MouseAction.WheelClick or MouseAction.LeftDoubleClick or MouseAction.RightDoubleClick or MouseAction.MiddleDoubleClick;
if (defined)
{
    string s = (string)converter.ConvertTo(null, culture, action, typeof(string));
}

Defensive patterns

Strategy: validation

Validate before calling

if (!Enum.IsDefined(typeof(MouseAction), mouseAction)) throw new ArgumentOutOfRangeException(nameof(mouseAction));

Type guard

static bool IsDefinedMouseAction(MouseAction a) => a is MouseAction.LeftClick or MouseAction.RightClick or MouseAction.MiddleClick or MouseAction.WheelClick or MouseAction.LeftDoubleClick or MouseAction.RightDoubleClick or MouseAction.MiddleDoubleClick;

Try / catch

try { s = (string)converter.ConvertTo(null, culture, mouseAction, typeof(string)); } catch (InvalidEnumArgumentException ex) { /* undefined MouseAction value */ }

Prevention

Never cast raw ints to MouseAction without Enum.IsDefined validation
Sanitize persisted gesture data when loading from config

When it happens

Trigger: Calling ConvertTo with a MouseAction cast from an undefined int (e.g. (MouseAction)42 or negative values).

Common situations: Serializing gesture settings that were loaded from untrusted/config data with out-of-range integers.

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/4c15134a95f6a86f. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Command/MouseActionConverter.cs:100

        public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
        {
            ArgumentNullException.ThrowIfNull(destinationType);

            if (value is null || destinationType != typeof(string))
                throw GetConvertToException(value, destinationType);

            MouseAction mouseAction = (MouseAction)value;
            return mouseAction switch
            {
                MouseAction.None => string.Empty,
                MouseAction.LeftClick => "LeftClick",
                MouseAction.RightClick => "RightClick",
                MouseAction.MiddleClick => "MiddleClick",
                MouseAction.WheelClick => "WheelClick",
                MouseAction.LeftDoubleClick => "LeftDoubleClick",
                MouseAction.RightDoubleClick => "RightDoubleClick",
                MouseAction.MiddleDoubleClick => "MiddleDoubleClick",
                _ => throw new InvalidEnumArgumentException(nameof(value), (int)mouseAction, typeof(MouseAction))
            };
        }

        /// <summary>
        /// Helper function similar to <see cref="Enum.IsDefined{MouseAction}(MouseAction)"/>, just lighter and faster.
        /// </summary>
        /// <param name="mouseAction">The value to test against.</param>
        /// <returns><see langword="true"/> if <paramref name="mouseAction"/> falls in enumeration range, <see langword="false"/> otherwise.</returns>
        internal static bool IsDefinedMouseAction(MouseAction mouseAction)
        {
            return mouseAction >= MouseAction.None && mouseAction <= MouseAction.MiddleDoubleClick;
        }
    }
}

View on GitHub (pinned to 81131a70a4)