JamesNK/Newtonsoft.Json · error · Exception

Could not create getter for {0}.

Error message

Could not create getter for {0}.

What it means

Thrown by ReflectionDelegateFactory.CreateGet(MemberInfo) when the supplied MemberInfo is neither a PropertyInfo nor a FieldInfo. The generic CreateGet only knows how to build value getters for fields and properties; any other member kind (method, event, constructor, nested type) falls through to this exception. It signals that an unexpected member type was fed into the getter pipeline.

Source

Thrown at Src/Newtonsoft.Json/Utilities/ReflectionDelegateFactory.cs:59

        public Func<T, object?> CreateGet<T>(MemberInfo memberInfo)
        {
            if (memberInfo is PropertyInfo propertyInfo)
            {
                // https://github.com/dotnet/corefx/issues/26053
                if (propertyInfo.PropertyType.IsByRef)
                {
                    throw new InvalidOperationException("Could not create getter for {0}. ByRef return values are not supported.".FormatWith(CultureInfo.InvariantCulture, propertyInfo));
                }

                return CreateGet<T>(propertyInfo);
            }

            if (memberInfo is FieldInfo fieldInfo)
            {
                return CreateGet<T>(fieldInfo);
            }

            throw new Exception("Could not create getter for {0}.".FormatWith(CultureInfo.InvariantCulture, memberInfo));
        }

        [RequiresDynamicCode(MiscellaneousUtils.AotWarning)]
        public Action<T, object?> CreateSet<T>(MemberInfo memberInfo)
        {
            if (memberInfo is PropertyInfo propertyInfo)
            {
                return CreateSet<T>(propertyInfo);
            }

            if (memberInfo is FieldInfo fieldInfo)
            {
                return CreateSet<T>(fieldInfo);
            }

            throw new Exception("Could not create setter for {0}.".FormatWith(CultureInfo.InvariantCulture, memberInfo));
        }

View on GitHub (pinned to 4f73e74372)

Solutions

1. Ensure only FieldInfo or PropertyInfo is passed to CreateGet — filter the member set beforehand.
2. For methods, use CreateMethodCall instead.
3. Audit custom contract resolvers / reflection helpers for the member kinds they hand to the delegate factory.

Example fix

// before
var getter = factory.CreateGet<object>(someMethodInfo);

// after
if (member is PropertyInfo p) getter = factory.CreateGet<object>(p);
else if (member is FieldInfo f)  getter = factory.CreateGet<object>(f);
else throw new InvalidOperationException($"Unsupported member: {member}");

if (member is not PropertyInfo and not FieldInfo) throw new InvalidOperationException($"Cannot get {member.MemberType}");
var getter = factory.CreateGet<object>(member);

static bool IsGettableMember(MemberInfo m) => m is PropertyInfo or FieldInfo;

When it happens

Trigger: Passing a MethodInfo, EventInfo, ConstructorInfo, or TypeInfo into CreateGet. Internally this can occur if a custom contract resolver or member-walking utility mistakenly treats a non-field/non-property member as a value source.

Common situations: Custom IContractResolver implementations, extension methods that iterate MemberInfo collections, or mismatches after upgrading Json.NET where member resolution logic changed.

Related errors

• Could not create setter for {0}.
• Error getting value from '{0}' on '{1}'.
• Error getting value from '{0}' on '{1}'.
• Error getting value from '{0}' on '{1}'.
• Target type {0} is not a value type or a non-abstract class.

AI-assisted analysis of JamesNK/Newtonsoft.Json@4f73e74372 (2026-08-07). Data as JSON: /api/errors/191172a1c2b93538. Report an issue: GitHub.