What causes "EnumType is only valid for enum fields." in XINCGer/Unity3DTraining?

Check field.FieldType == FieldType.Enum before accessing EnumType.

XINCGer/Unity3DTraining · error · InvalidOperationException

EnumType is only valid for enum fields.

Error message

EnumType is only valid for enum fields.

What it means

The FieldDescriptor.EnumType property only holds a value when the field's type is FieldType.Enum. Reading it on any other field throws InvalidOperationException. This is a misuse guard: the enum descriptor simply does not exist for non-enum fields.

Solutions

Check field.FieldType == FieldType.Enum before accessing EnumType.
Access it inside the enum branch of your field-type switch in reflection code.
If the field may be either, use pattern checks (fieldType switch) rather than direct property access.

Example fix

// before
var enumType = field.EnumType;
// after
var enumType = field.FieldType == FieldType.Enum ? field.EnumType : null;

Defensive patterns

Strategy: type-guard

Validate before calling

var enumType = field.FieldType == FieldType.Enum ? field.EnumType : null;

Type guard

bool TryGetEnumType(FieldDescriptor f, out EnumDescriptor ed)
{ ed = f.FieldType == FieldType.Enum ? f.EnumType : null; return ed != null; }

Try / catch

EnumDescriptor ed = null;
try { ed = field.EnumType; }
catch (InvalidOperationException) { /* not an enum field */ }

Prevention

Always branch reflection logic on FieldType before touching type-specific properties.
Handle both message and enum branches in field-walking utilities.
Write a helper accessor that returns null instead of throwing.

When it happens

Trigger: Accessing descriptor.EnumType on a field whose FieldType is a primitive, string, bytes, or message, e.g. reflection code that assumes every field has both MessageType and EnumType.

Common situations: Generic reflection loops over message fields that access EnumType unconditionally; code copied from a field that happened to be an enum.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of XINCGer/Unity3DTraining@016f98412e (2026-09-12). Data as JSON: /api/errors/02acda4d58f39d5c. Report an issue: GitHub.

Appendix: source

Thrown at NetWorkAndResources/Socket_Protobuff/Assets/Plugins/Google.Protobuf/Reflection/FieldDescriptor.cs:273

        {
            if (other.ContainingType != ContainingType)
            {
                throw new ArgumentException("FieldDescriptors can only be compared to other FieldDescriptors " +
                                            "for fields of the same message type.");
            }
            return FieldNumber - other.FieldNumber;
        }

        /// <summary>
        /// For enum fields, returns the field's type.
        /// </summary>
        public EnumDescriptor EnumType
        {
            get
            {
                if (fieldType != FieldType.Enum)
                {
                    throw new InvalidOperationException("EnumType is only valid for enum fields.");
                }
                return enumType;
            }
        }

        /// <summary>
        /// For embedded message and group fields, returns the field's type.
        /// </summary>
        public MessageDescriptor MessageType
        {
            get
            {
                if (fieldType != FieldType.Message)
                {
                    throw new InvalidOperationException("MessageType is only valid for message fields.");
                }
                return messageType;
            }

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