What causes "SR.GetterOrSetterRequired" in dotnet/wpf?

Pass at least one valid accessor MethodInfo (getter or setter).

dotnet/wpf · error · ArgumentNullException

SR.GetterOrSetterRequired

Error message

SR.GetterOrSetterRequired

What it means

The attachable-member XamlMember constructor requires at least one of 'getter' or 'setter' to be a non-null MethodInfo. When both are null it throws ArgumentNullException whose message is SR.GetterOrSetterRequired. Without an accessor the member cannot be read or written.

Solutions

Pass at least one valid accessor MethodInfo (getter or setter).
Fix the reflection lookup (method name must be 'Get<Name>'/'Set<Name>' and public static) so an accessor is found.
Verify you are not accidentally passing variables that were assigned null earlier.

Example fix

// before
var member = new XamlMember("MyAttached", null, null, schemaContext, invoker, reflector);
// after
var getter = declaringType.GetMethod("GetMyAttached", BindingFlags.Public | BindingFlags.Static);
var member = new XamlMember("MyAttached", getter, null, schemaContext, invoker, reflector);

Defensive patterns

Strategy: validation

Validate before calling

if (getter is null && setter is null) throw new ArgumentException("At least one of getter or setter is required");

Type guard

bool HasAccessor(MethodInfo g, MethodInfo s) => g is not null || s is not null;

Prevention

Verify reflection lookups for Get/Set accessors return non-null before constructing.
Log accessor lookups to catch broken naming conventions (Get<Name>/Set<Name>).

When it happens

Trigger: Calling new XamlMember(attachablePropertyName, getter: null, setter: null, schemaContext, invoker, reflector) — i.e. both accessor MethodInfos are null.

Common situations: Reflecting attachable properties where the getter and setter are discovered via reflection (e.g. Type.GetMethod with loose binding flags) and neither lookup matched.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/0983f9c22c75f3ee. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlMember.cs:107

            XamlSchemaContext schemaContext)
            :this(attachablePropertyName, getter, setter, schemaContext, null)
        {
        }

        public XamlMember(string attachablePropertyName, MethodInfo getter, MethodInfo setter,
            XamlSchemaContext schemaContext, XamlMemberInvoker invoker)
            :this(attachablePropertyName, getter, setter, schemaContext, invoker, new MemberReflector(getter, setter, isEvent: false))
        {
        }

        internal XamlMember(string attachablePropertyName, MethodInfo getter, MethodInfo setter,
            XamlSchemaContext schemaContext, XamlMemberInvoker invoker, MemberReflector reflector)
        {
            ArgumentNullException.ThrowIfNull(schemaContext);
            MethodInfo accessor = getter ?? setter;
            if (accessor is null)
            {
                throw new ArgumentNullException(SR.GetterOrSetterRequired, (Exception)null);
            }

            _name = attachablePropertyName ?? throw new ArgumentNullException(nameof(attachablePropertyName));

            ValidateGetter(getter, nameof(getter));
            ValidateSetter(setter, nameof(setter));

            _declaringType = schemaContext.GetXamlType(accessor.DeclaringType);
            _reflector = reflector;
            _memberType = MemberType.Attachable;
            _reflector.Invoker = invoker;
            _underlyingMember.Value = getter ?? setter;
        }

        // Known attachable event
        public XamlMember(string attachableEventName, MethodInfo adder, XamlSchemaContext schemaContext)
            :this(attachableEventName, adder, schemaContext, null)
        {

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