dotnet/wpf · error · InvalidEnumArgumentException

InvalidEnumArgumentException("modifiers", (int)modifiers…

Error message

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

What it means

The private KeyGesture constructor validates that the ModifierKeys value is a defined combination (via ModifierKeysConverter.IsDefinedModifierKeys) and throws InvalidEnumArgumentException for 'modifiers' otherwise. This catches out-of-range or undefined bit values cast into ModifierKeys.

Solutions

Only pass ModifierKeys values composed of the defined enum members (None, Alt, Control, Shift, Windows)
Validate with ModifierKeysConverter.IsDefinedModifierKeys before constructing
Clamp/parse modifiers from config through the enum converter rather than raw casts

Example fix

// before
var gesture = new KeyGesture(Key.A, (ModifierKeys)rawInt);
// after
var modifiers = (ModifierKeys)rawInt;
if (ModifierKeysConverter.IsDefinedModifierKeys(modifiers))
{
    var gesture = new KeyGesture(Key.A, modifiers);
}

Defensive patterns

Strategy: validation

Validate before calling

if (!ModifierKeysConverter.IsDefinedModifierKeys(modifiers)) throw new ArgumentOutOfRangeException(nameof(modifiers));

Type guard

static bool IsDefinedModifiers(ModifierKeys m) => ModifierKeysConverter.IsDefinedModifierKeys(m);

Try / catch

try { var g = new KeyGesture(key, modifiers); } catch (InvalidEnumArgumentException ex) { /* undefined modifiers value */ }

Prevention

Never cast raw ints to ModifierKeys without validation
Compose modifiers only from defined enum members
Parse modifier strings through ModifierKeysConverter

When it happens

Trigger: Calling a public KeyGesture constructor with (ModifierKeys)value where the int is not a defined enum combination (e.g. (ModifierKeys)99 or negative values).

Common situations: Deserializing gestures from config where modifier ints come from user data or another system's flag values.

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/fdbfb8a5146b2201. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Command/KeyGesture.cs:91

        /// <param name="key">Key</param>
        /// <param name="modifiers">Modifiers</param>
        /// <param name="validateGesture">If true, throws an exception if the key and modifier are not valid</param>
        internal KeyGesture(Key key, ModifierKeys modifiers, bool validateGesture)
            : this(key, modifiers, String.Empty, validateGesture)
        {
        }

        /// <summary>
        /// Private constructor that does the real work.
        /// </summary>
        /// <param name="key">Key</param>
        /// <param name="modifiers">Modifiers</param>
        /// <param name="displayString">display string</param>
        /// <param name="validateGesture">If true, throws an exception if the key and modifier are not valid</param>
        private KeyGesture(Key key, ModifierKeys modifiers, string displayString, bool validateGesture)
        {
            if(!ModifierKeysConverter.IsDefinedModifierKeys(modifiers))
                throw new InvalidEnumArgumentException("modifiers", (int)modifiers, typeof(ModifierKeys));

            if(!IsDefinedKey(key))
                throw new InvalidEnumArgumentException("key", (int)key, typeof(Key));

            ArgumentNullException.ThrowIfNull(displayString);

            if (validateGesture && !IsValid(key, modifiers))
            {
                throw new NotSupportedException(SR.Format(SR.KeyGesture_Invalid, modifiers, key));
            }

            _modifiers = modifiers;
            _key = key;
            _displayString = displayString;
        }
#endregion Constructors

        //------------------------------------------------------

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