dotnet/wpf · error · ArgumentException

The type of this parameter does not support a required…

Error message

The type of this parameter does not support a required interface

What it means

Verify.TypeSupportsInterface throws ArgumentException when the runtime Type of a parameter does not implement the required interface (checked via type.GetInterface(interfaceType.Name)). It is a static contract guard used inside WPF to reject arguments whose concrete type lacks a needed interface.

Solutions

1. Ensure the parameter's concrete type implements the required interface before passing it.
2. Use the interface name from the call site / parameterName to identify the missing interface and add the implementation.
3. If the type is external, write an adapter/wrapper class that implements the interface and forwards to it.

Example fix

// before
helper.SetValue(myCustomObject); // does not implement ISupportInitialize
// after
class MyCustomObject : ISupportInitialize { ... }
helper.SetValue(myCustomObject);

if (requiredInterface.IsInstanceOfType(argument)) { api.Call(argument); }

static bool Implements<TReq>(object o) => o is TReq; // or typeof(TReq).IsInstanceOfType(o)

try { api.Call(obj); }
catch (ArgumentException ex) when (ex.Message.Contains("interface")) { /* substitute compliant type */ }

When it happens

Trigger: Passing an object whose Type does not implement interfaceType to a WPF API that calls Verify.TypeSupportsInterface (or directly calling Verify.TypeSupportsInterface with a mismatched type/interface pair).

Common situations: Refactors that drop an interface implementation from a class still passed to legacy APIs; reflection-based object construction producing a type that no longer satisfies the contract; wrong generic or custom substitute type used in tests.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• The parameter must implement interface
• SR.IncorrectLocatorPartType
• SR.Invalid_IInputElement
• SR.ITypeDataObject_Not_Implemented
• SR.Mismatched_RoutedEvent

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/89cbc1561383e3ab. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Standard/Verify.cs:257

        [DebuggerStepThrough]
        public static void BoundedDoubleInc(double lowerBoundInclusive, double value, double upperBoundInclusive, string message, string parameter)
        {
            if (value < lowerBoundInclusive || value > upperBoundInclusive)
            {
                throw new ArgumentException(message, parameter);
            }
        }
        
        [DebuggerStepThrough]
        public static void TypeSupportsInterface(Type type, Type interfaceType, string parameterName)
        {
            Assert.IsNeitherNullNorEmpty(parameterName);
            Verify.IsNotNull(type, "type");
            Verify.IsNotNull(interfaceType, "interfaceType");

            if (type.GetInterface(interfaceType.Name) == null)
            {
                throw new ArgumentException("The type of this parameter does not support a required interface", parameterName);
            }
        }
        
        [DebuggerStepThrough]
        public static void FileExists(string filePath, string parameterName)
        {
            Verify.IsNeitherNullNorEmpty(filePath, parameterName);
            if (!File.Exists(filePath))
            {
                throw new ArgumentException($"No file exists at \"{filePath}\"", parameterName);
            }
        }
        
        [DebuggerStepThrough]
        internal static void ImplementsInterface(object parameter, Type interfaceType, string parameterName)
        {
            Assert.IsNotNull(parameter);
            Assert.IsNotNull(interfaceType);

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