dotnet/wpf · error · InvalidEnumArgumentException

InvalidEnumArgumentException("modifiers", (int)modifiers…

Error message

InvalidEnumArgumentException("modifiers", (int)modifiers, typeof(ModifierKeys))

What it means

The same MouseGesture(MouseAction, ModifierKeys) constructor also validates that modifiers is a defined ModifierKeys value; an undefined value throws InvalidEnumArgumentException naming the 'modifiers' parameter.

Solutions

Use only ModifierKeys enum members or valid combinations of them via the | operator.
Validate with ModifierKeysConverter.IsDefinedModifierKeys(modifiers) (or mask-check against the defined flags) before constructing.
Normalize incoming modifier data at deserialization time to the nearest valid ModifierKeys.

Example fix

// before
var gesture = new MouseGesture(MouseAction.RightClick, (ModifierKeys)rawBits);
// after
var mods = (ModifierKeys)rawBits & (ModifierKeys.Alt | ModifierKeys.Control | ModifierKeys.Shift | ModifierKeys.Windows);
var gesture = new MouseGesture(MouseAction.RightClick, mods);

Defensive patterns

Strategy: validation

Validate before calling

var allowed = ModifierKeys.Alt | ModifierKeys.Control | ModifierKeys.Shift | ModifierKeys.Windows;
if (((ModifierKeys)raw & ~allowed) != 0 || (ModifierKeys)raw == 0 && raw != 0) throw new ArgumentOutOfRangeException(nameof(raw));
var gesture = new MouseGesture(action, (ModifierKeys)raw);

Type guard

static bool IsValidModifiers(ModifierKeys m) => (m & ~(ModifierKeys.Alt|ModifierKeys.Control|ModifierKeys.Shift|ModifierKeys.Windows)) == 0;

Try / catch

try { var g = new MouseGesture(action, mods); } catch (InvalidEnumArgumentException ex) { /* normalize modifiers and retry */ }

Prevention

Build modifier values only from named ModifierKeys members with |
Mask unknown bits out of persisted modifier ints
Round-trip test serialized gestures

When it happens

Trigger: new MouseGesture(MouseAction.LeftClick, (ModifierKeys)64) — an int cast to ModifierKeys outside defined members (None, Alt, Control, Shift, Windows and defined combinations).

Common situations: Persisting modifier state as an int and combining flags ad hoc, or macOS/Linux key mappings translated to undefined ModifierKeys bits.

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/85fe4bcd053972b3. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Command/MouseGesture.cs:61

        ///  constructor
        /// </summary>
        /// <param name="mouseAction">Mouse Action</param>
        public MouseGesture(MouseAction mouseAction): this(mouseAction, ModifierKeys.None)
        {
        }

        /// <summary>
        ///  Constructor
        /// </summary>
        /// <param name="mouseAction">Mouse Action</param>
        /// <param name="modifiers">Modifiers</param>
        public MouseGesture( MouseAction mouseAction,ModifierKeys modifiers)   // acclerator action
        {
            if (!MouseGesture.IsDefinedMouseAction(mouseAction))
                throw new InvalidEnumArgumentException("mouseAction", (int)mouseAction, typeof(MouseAction));

            if (!ModifierKeysConverter.IsDefinedModifierKeys(modifiers))
                throw new InvalidEnumArgumentException("modifiers", (int)modifiers, typeof(ModifierKeys));

            _modifiers = modifiers;
            _mouseAction = mouseAction;

            //AttachClassListeners();
        }
#endregion Constructors
        
        //------------------------------------------------------
        //
        //  Public Methods
        //
        //------------------------------------------------------

#region Public Methods
        /// <summary>
        /// Action 
        /// </summary>

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