Unity-Technologies/UnityCsReference · error · ArgumentException

Parameter enumValue must be of type System.Enum

Error message

Parameter enumValue must be of type System.Enum

What it means

Thrown by the deprecated EnumMaskFieldInternal (no-label overload) when enumValue.GetType().IsEnum is false. Because the parameter is typed 'Enum', passing null throws NullReferenceException at .GetType() before reaching this check; the ArgumentException is reached only when a non-enum value is boxed as System.Enum via an invalid cast. The whole method is [Obsolete] — use EnumFlagsField.

Source

Thrown at Editor/Mono/EditorGUI.EnumMaskField.deprecated.cs:91

        public static Enum EnumMaskPopup(Rect position, GUIContent label, Enum selected, GUIStyle style)
        {
            int changedFlags;
            bool changedToValue;
            return EnumMaskPopup(position, label, selected, out changedFlags, out changedToValue, style);
        }

        [Obsolete("EnumMaskField has been deprecated. Use EnumFlagsField instead.")]
        static Enum EnumMaskField(Rect position, GUIContent label, Enum enumValue, GUIStyle style, out int changedFlags, out bool changedToValue)
        {
            return DoEnumMaskField(position, label, enumValue, style, out changedFlags, out changedToValue);
        }

        [Obsolete("EnumMaskField has been deprecated. Use EnumFlagsField instead.")]
        static Enum EnumMaskFieldInternal(Rect position, Enum enumValue, GUIStyle style)
        {
            Type enumType = enumValue.GetType();
            if (!enumType.IsEnum)
                throw new ArgumentException("Parameter enumValue must be of type System.Enum", "enumValue");

            var names = Array.ConvertAll(Enum.GetNames(enumType), ObjectNames.NicifyVariableName);
            int flags = MaskFieldGUIDeprecated.DoMaskField(
                IndentedRect(position),
                GUIUtility.GetControlID(s_MaskField, FocusType.Keyboard, position),
                Convert.ToInt32(enumValue),
                names, style);
            return EnumDataUtility.IntToEnumFlags(enumType, flags);
        }

        [Obsolete("EnumMaskField has been deprecated. Use EnumFlagsField instead.")]
        static Enum EnumMaskFieldInternal(Rect position, GUIContent label, Enum enumValue, GUIStyle style)
        {
            Type enumType = enumValue.GetType();
            if (!enumType.IsEnum)
                throw new ArgumentException("Parameter enumValue must be of type System.Enum", "enumValue");

            var id = GUIUtility.GetControlID(s_MaskField, FocusType.Keyboard, position);

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Migrate to EditorGUI.EnumFlagsField / EnumFlagsFieldPopup, which carry a proper generic/Enum constraint.
2. Type-check before calling: if (value == null || !value.GetType().IsEnum) reject.
3. Ensure the source of the value is statically typed as a concrete enum, not object.

Example fix

// before
Enum v = (Enum)(object)someInt;
EditorGUI.EnumMaskField(rect, v);
// after
[Flags] enum MyFlags { A = 1, B = 2 }
MyFlags v = MyFlags.A | MyFlags.B;
EditorGUI.EnumFlagsField(rect, v);

if (enumValue == null || !enumValue.GetType().IsEnum)
    throw new ArgumentException("enumValue must be an enum", nameof(enumValue));

static bool IsEnumValue(Enum v) => v != null && v.GetType().IsEnum;

When it happens

Trigger: Calling EditorGUI.EnumMaskField (deprecated) with a value that is not actually an enum, e.g. an int or a class boxed and cast to Enum via unsafe means. Reachable through reflection-driven generic code that lost the enum constraint.

Common situations: Legacy code predating EnumFlagsField; reflection helpers that build mask fields generically and pass a boxed non-enum; ported UI code.

Related errors

• Given rpAssetType must derive from RenderPipelineAsset
• EditorApplication.OpenScene() cannot be called when in the U
• object is not a EditorBuildSettingsScene
• Check the connected players list instead
• Unknown opt out decision type

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/905a3db242768b36. Report an issue: GitHub.