stride3d/stride · error · ArgumentException

The object passed to this value converter is not a type.

Error message

The object passed to this value converter is not a type.

What it means

UnderlyingTypeConverter resolves the underlying type of a Nullable<T>: given typeof(int?) it returns typeof(int); given a non-nullable Type it returns the value unchanged. It throws this ArgumentException from Convert (UnderlyingType.cs:21) when the bound value is not a System.Type instance at all.

Solutions

Bind a value that is a System.Type (e.g. `Binding Path="."` on a Type-typed source or `{x:Type SomeType}`).
If you have a type name string, resolve it first with Type.GetType(name) before passing it.
For object instances, use `{Binding Source={x:Type local:MyType}}` or bind the instance's GetType() result.
Guard with `value is Type` before calling Convert, or wrap the converter to pass through non-Type values.

Example fix

// before
var r = converter.Convert("Int32", typeof(Type), null, culture); // throws (string, not Type)
// after
var r = converter.Convert(typeof(int?), typeof(Type), null, culture); // returns typeof(int)

Defensive patterns

Strategy: type-guard

Validate before calling

bool ok = value is System.Type;

Type guard

static bool IsType(object v) => v is System.Type;

Try / catch

try { return converter.Convert(value, typeof(Type), null, culture); }
catch (ArgumentException) { return value; }

Prevention

Feed the converter with {x:Type ...} markup extensions or Type-typed properties, not type-name strings.
Resolve name strings with Type.GetType before binding if only names are available.
Remember non-nullable Types pass through unchanged; the error is only for non-Type inputs.

When it happens

Trigger: Binding a non-Type value into this converter — e.g. binding an object instance instead of its type, a type name string, or null — then calling Convert; also direct calls passing arbitrary objects.

Common situations: Binding to a property like `GetType()` incorrectly, passing the type's FullName string instead of the Type, binding a generic collection item while expecting the item's type, tests using dummy values.

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

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/a277d9356eb6b06b. Report an issue: GitHub.

Appendix: source

Thrown at sources/presentation/Stride.Core.Presentation.Wpf/ValueConverters/UnderlyingType.cs:21

using System;
using System.Globalization;
using Stride.Core.Annotations;

namespace Stride.Core.Presentation.ValueConverters
{
    /// <summary>
    /// This converter convert a <see cref="Nullable"/> type to its underlying type. If the type is not nullable, it returns the type itself.
    /// </summary>
    public class UnderlyingType : OneWayValueConverter<UnderlyingType>
    {
        /// <inheritdoc/>
        [NotNull]
        public override object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            var type = value as Type;
            if (type == null)
            {
                throw new ArgumentException("The object passed to this value converter is not a type.");
            }
            return Nullable.GetUnderlyingType(type) ?? value;
        }
    }
}

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