lepoco/wpfui · error · ArgumentException

is not type

Error message

{nameof(value)} is not type: {typeof(TEnum)}

What it means

EnumToBoolConverter<TEnum>.Convert requires the bound value to be of the converter's generic enum type TEnum. It throws ArgumentException when value is not assignable to TEnum. The converter compares a bound enum (e.g. ContentDialogButton) against a ConverterParameter enum for equality, so the bound value's type must match exactly.

Solutions

1. Bind the converter only to properties of the exact TEnum type.
2. If the source is an int, add a value converter that casts to the enum first, or change the source property type.
3. Handle null/nullable sources by ensuring the property has a default enum value.

Example fix

<!-- before: DefaultButton exposed as int -->
<CheckBox IsChecked="{Binding Mode, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static local:Mode.Simple}}" />

<!-- after: bind a typed enum property -->
<CheckBox IsChecked="{Binding ModeEnum, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static local:Mode.Simple}}" />

if (value is not TEnum)
{
    throw new ArgumentException($"Bound value must be {typeof(TEnum)}.", nameof(value));
}

static bool IsCorrectEnumType(object? value) => value is TEnum;

try { return converter.Convert(value, targetType, parameter, culture); }
catch (ArgumentException ex) when (ex.Message.Contains("is not type"))
{
    _logger.LogError(ex, "EnumToBoolConverter bound to wrong value type");
    return DependencyProperty.UnsetValue;
}

When it happens

Trigger: Binding the converter to a property whose type is not TEnum - e.g. an int, a string, an object, or a different enum - while the converter is generic over ContentDialogButton.

Common situations: Binding DefaultButton-like properties where the source exposes an int or nullable enum; binding a wrong enum type; null value when the source property is not initialised.

Related errors

• ExceptionEnumToBooleanConverterParameterMustBeAnEnumName
• ExceptionEnumToBooleanConverterValueMustBeAnEnum
• is not type
• Unsupported button type
• Cannot apply backdrop effect if ExtendsContentIntoTitleBar…

AI-assisted analysis of lepoco/wpfui@ffebacd610 (2026-08-13). Data as JSON: /api/errors/37d88fe68396327d. Report an issue: GitHub.

Appendix: source

Thrown at src/Wpf.Ui/Converters/EnumToBoolConverter.cs:17

// This Source Code Form is subject to the terms of the MIT License.
// If a copy of the MIT was not distributed with this file, You can obtain one at https://opensource.org/licenses/MIT.
// Copyright (C) Leszek Pomianowski and WPF UI Contributors.
// All Rights Reserved.

using System.Windows.Data;

namespace Wpf.Ui.Converters;

internal class EnumToBoolConverter<TEnum> : IValueConverter
    where TEnum : Enum
{
    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
    {
        if (value is not TEnum valueEnum)
        {
            throw new ArgumentException($"{nameof(value)} is not type: {typeof(TEnum)}");
        }

        if (parameter is not TEnum parameterEnum)
        {
            throw new ArgumentException($"{nameof(parameter)} is not type: {typeof(TEnum)}");
        }

        return EqualityComparer<TEnum>.Default.Equals(valueEnum, parameterEnum);
    }

    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

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