dotnet/wpf · error · InvalidEnumArgumentException

InvalidEnumArgumentException("mode", (int)mode…

Error message

InvalidEnumArgumentException("mode", (int)mode, typeof(InputMode))

What it means

InputReport's private Validate_InputMode throws System.ComponentModel.InvalidEnumArgumentException when the mode parameter is not InputMode.Foreground or InputMode.Sink. This is constructor-time argument validation because InputMode has exactly two defined members and anything else indicates a bad cast or corrupted data.

Solutions

Only pass InputMode.Foreground or InputMode.Sink when constructing InputReport instances.
Validate numeric sources before casting: if (n != (int)InputMode.Foreground && n != (int)InputMode.Sink) throw/reject.
Wrap construction in try-catch for InvalidEnumArgumentException when handling external input data.

Example fix

// before
var report = new InputReport(source, type, (InputMode)rawInt, timestamp);
// after
var mode = rawInt == (int)InputMode.Sink ? InputMode.Sink : InputMode.Foreground;
var report = new InputReport(source, type, mode, timestamp);

Defensive patterns

Strategy: validation

Validate before calling

if (mode is not (InputMode.Foreground or InputMode.Sink))
    throw new InvalidDataException($"Invalid InputMode: {mode}");

Type guard

static bool IsValidInputMode(InputMode mode) =>
    mode is InputMode.Foreground or InputMode.Sink;

Try / catch

try { var report = new InputReport(src, type, mode, ts); }
catch (InvalidEnumArgumentException) { /* log and drop bad report */ }

Prevention

Whitelist raw ints against defined InputMode values before casting.
Never deserialize InputMode without validation.
Add Debug.Assert(IsValidInputMode(mode)) in custom provider code during development.

When it happens

Trigger: Constructing InputReport (or a subclass like RawKeyboardInputReport) with an undefined InputMode value, e.g. (InputMode)3 or a value deserialized from untrusted data.

Common situations: Custom input provider code casting raw ints to InputMode; reflection/serialization round-trips that produce out-of-range enum values; tests feeding synthetic input reports.

Understand the failure class

Background: "invalid argument", "unknown mode", "not supported": invalid enum-like argument errors explained — this error's family across 19 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/65af9c7e5300ce96. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/InputReport.cs:76

        /// <summary>
        ///     Read-only access to the time when the input occurred.
        /// </summary>
        public int Timestamp {get {return _timestamp;}}

        /// <summary>
        /// There is a proscription against using Enum.IsDefined().  (it is slow)
        /// so we write these PRIVATE validate routines instead.
        /// </summary>
        private void Validate_InputMode( InputMode mode )
        {
            switch( mode )
            {
                case InputMode.Foreground:
                case InputMode.Sink:
                    break;
                default:
                    throw new  System.ComponentModel.InvalidEnumArgumentException("mode", (int)mode, typeof(InputMode));
            }
        }

        /// <summary>
        /// There is a proscription against using Enum.IsDefined().  (it is slow)
        /// so we write these PRIVATE validate routines instead.
        /// </summary>
        private void Validate_InputType( InputType type )
        {
            switch( type )
            {
                case InputType.Keyboard:
                case InputType.Mouse:
                case InputType.Stylus:
                case InputType.Hid:
                case InputType.Text:
                case InputType.Command:
                    break;

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