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

Pass at least one non-null argument — typically the converter Type or the target XamlType.

dotnet/wpf · error · ArgumentException

SR.ArgumentRequired

Error message

SR.ArgumentRequired

What it means

The XamlValueConverter(Type, XamlType, name) constructor throws ArgumentException('ArgumentRequired') when all three parameters are null. A value converter must be identifiable by at least one of: its converter CLR type, its target XamlType, or an explicit name — otherwise instances could not be named, cached, or compared (IEquatable). At least one identifier is therefore mandatory.

Solutions

Pass at least one non-null argument — typically the converter Type or the target XamlType.
Provide a name when neither type nor target applies so the converter can still be identified.
Guard the construction site: validate that at least one argument is non-null before constructing.
Catch ArgumentException at the boundary if inputs come from external configuration and surface a clear config error.

Example fix

// before
var conv = new XamlValueConverter<ValueConverter>(maybeType, maybeTarget, null);
// after
if (maybeType is null && maybeTarget is null) throw new InvalidOperationException("converter requires a type or target");
var conv = new XamlValueConverter<ValueConverter>(maybeType, maybeTarget, null);

Defensive patterns

Strategy: validation

Validate before calling

if (converterType is null && targetType is null && name is null) throw new ArgumentException("At least one of converterType/targetType/name is required");

Type guard

static bool ConverterIdentifiable(Type t, XamlType target, string name) => t is not null || target is not null || name is not null;

Try / catch

try { var c = new XamlValueConverter<T>(type, target, name); } catch (ArgumentException ex) { /* all-null converter descriptor */ }

Prevention

Always pass the converter Type or target XamlType when constructing converters.
Validate configuration-driven converter inputs before construction.
Supply an explicit name for converter identification when types are unknown.
Centralize converter construction in one factory that enforces this invariant.

When it happens

Trigger: new XamlValueConverter<TConverterBase>(null, null, null) — e.g. code that conditionally builds converters where every input defaulted to null, or deserialization/constructor plumbing that forgot to pass the converter type or target type.

Common situations: Generic converter-factory code where a config-driven converterType lookup returned null and fallbacks (targetType, name) were also null; refactoring that made previously-supplied arguments optional; unit tests constructing a 'blank' converter.

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/acd7cf18b85d7142. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/Schema/XamlValueConverter.cs:33

        private TConverterBase _instance;
        private ThreeValuedBool _isPublic;

        private volatile bool _instanceIsSet; // volatile for the same reason as valid flags in TypeReflector/MemberReflector

        public string Name { get; }
        public Type ConverterType { get; }
        public XamlType TargetType { get; }

        public XamlValueConverter(Type converterType, XamlType targetType)
            :this(converterType, targetType, null)
        {
        }

        public XamlValueConverter(Type converterType, XamlType targetType, string name)
        {
            if (converterType is null && targetType is null && name is null)
            {
                throw new ArgumentException(SR.Format(SR.ArgumentRequired, $"{nameof(converterType)}, {nameof(targetType)}, {nameof(name)}"));
            }

            ConverterType = converterType;
            TargetType = targetType;
            Name = name ?? GetDefaultName();
        }

        public TConverterBase ConverterInstance
        {
            get
            {
                if (!_instanceIsSet)
                {
                    Interlocked.CompareExchange(ref _instance, CreateInstance(), null);
                    _instanceIsSet = true;
                }

                return _instance;

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