stride3d/stride · error · InvalidOperationException

This multi converter must be invoked with at least two…

Error message

This multi converter must be invoked with at least two elements

What it means

AllEqualMultiConverter.Convert throws this InvalidOperationException when the MultiBinding supplies fewer than two values, since comparing 'all equal' is meaningless with zero or one element. The converter's contract requires at least two bound values.

Solutions

Ensure the MultiBinding contains at least two child Bindings
Verify the converter is attached via <MultiBinding.Converter>, not a single Binding
Check child bindings for errors so values are not pruned to fewer than two

Example fix

// before
<Binding Path="A" Converter={StaticResource AllEqualMultiConverter}/>
// after
<MultiBinding Converter="{StaticResource AllEqualMultiConverter}">
  <Binding Path="A"/>
  <Binding Path="B"/>
</MultiBinding>

Defensive patterns

Strategy: validation

Validate before calling

if (values == null || values.Length < 2)
    throw new InvalidOperationException("MultiBinding must supply at least two values");

Type guard

bool HasTwoValues(object[] v) => v != null && v.Length >= 2;

Try / catch

try { result = AllEqualMultiConverter.Instance.Convert(values, targetType, param, culture); }
catch (InvalidOperationException ex) { Log.Warn("Multibinding under-populated", ex); }

Prevention

Always use MultiBinding with >= 2 child Bindings for multi converters
Never attach multi converters to a plain Binding
Review XAML for dropped/removed nested Bindings
Convert to the WPF fallback values instead by passing a bool parameter

When it happens

Trigger: An IMultiValueConverter binding with a single child binding; all but one child binding failing to produce values; incorrectly wiring the converter to a plain Binding instead of a MultiBinding.

Common situations: XAML MultiBinding missing a nested Binding/Path element; a binding silently dropping values so the array shrinks; copy-pasting the converter into a normal Binding.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/149feda63e4a394c. Report an issue: GitHub.

Appendix: source

Thrown at sources/presentation/Stride.Core.Presentation.Wpf/ValueConverters/AllEqualMultiConverter.cs:19

// Copyright (c) .NET Foundation and Contributors (https://dotnetfoundation.org/ & https://stride3d.net) and Silicon Studio Corp. (https://www.siliconstudio.co.jp)
// Distributed under the MIT license. See the LICENSE.md file in the project root for more information.

using System;
using System.Globalization;
using System.Linq;
using System.Windows;
using Stride.Core.Annotations;
using Stride.Core.Presentation.Internal;

namespace Stride.Core.Presentation.ValueConverters
{
    public class AllEqualMultiConverter : OneWayMultiValueConverter<AllEqualMultiConverter>
    {
        [NotNull]
        public override object Convert([NotNull] object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            if (values.Length < 2)
                throw new InvalidOperationException("This multi converter must be invoked with at least two elements");

            var fallbackValue = parameter is bool && (bool)parameter;
            var first = values[0];
            var result = values.All(x => x == DependencyProperty.UnsetValue ? fallbackValue : Equals(x, first));
            return result.Box();
        }
    }
}

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