stride3d/stride · error · ArgumentException

The parameter of the ConvertBack method of this converter…

Error message

The parameter of the ConvertBack method of this converter must be a an instance of the Thickness structure.

What it means

SumThickness.Convert requires the ConverterParameter to be a Thickness so it can add Left/Top/Right/Bottom component-wise. It throws this ArgumentException from Convert (SumThickness.cs:28) when `parameter` is not a Thickness.

Solutions

Supply the parameter as a Thickness resource: `<Thickness x:Key="Delta">1,2,3,4</Thickness>` then `ConverterParameter="{StaticResource Delta}"`.
Set the converter parameter in code-behind/ViewModel as `new Thickness(...)`.
Use a Binding (with a Thickness-typed source) instead of ConverterParameter.
Guard with `if (parameter is Thickness)` before calling Convert.

Example fix

// before
<Border local:SumThickness.ConverterParameter="1,2,3,4" /> <!-- string, throws -->
// after
<sys:Thickness x:Key="Pad">1,2,3,4</sys:Thickness>
<Border local:SumThickness.ConverterParameter="{StaticResource Pad}" />

Defensive patterns

Strategy: type-guard

Validate before calling

bool ok = parameter is System.Windows.Thickness;

Type guard

static bool HasValidParameter(object p) => p is System.Windows.Thickness;

Try / catch

try { return converter.Convert(value, typeof(Thickness), param, culture); }
catch (ArgumentException) { return Binding.DoNothing; }

Prevention

Use <Thickness> resources for ConverterParameter instead of strings.
Remember XAML ConverterParameter attributes can only yield strings — never a Thickness.
Prefer MultiBinding or a dedicated converter if you need string-parsed offsets.

When it happens

Trigger: Setting ConverterParameter to a string like "1,2,3,4" or a double in XAML while using SumThickness in a forward (Convert) binding; calling Convert directly with a non-Thickness parameter.

Common situations: XAML ConverterParameter only produces strings, so this throws for nearly every XAML-based usage unless a Size/Thickness resource is supplied; copying patterns from converters that parse string parameters.

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/38422323fec4acf7. Report an issue: GitHub.

Appendix: source

Thrown at sources/presentation/Stride.Core.Presentation.Wpf/ValueConverters/SumThickness.cs:28

{
    /// <summary>
    /// This converter will sum a given <see cref="Thickness"/> with a <see cref="Thickness"/> passed as parameter. You can use
    /// the <see cref="MarkupExtensions.ThicknessExtension"/> markup extension to easily pass one, with the following syntax: {sd:Thickness (arguments)}. 
    /// </summary>
    [ValueConversion(typeof(Thickness), typeof(Thickness))]
    public class SumThickness : ValueConverterBase<SumThickness>
    {
        /// <inheritdoc/>
        [NotNull]
        public override object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (!(value is Thickness))
            {
                throw new ArgumentException("The value of the ConvertBack method of this converter must be a an instance of the Thickness structure.");
            }
            if (!(parameter is Thickness))
            {
                throw new ArgumentException("The parameter of the ConvertBack method of this converter must be a an instance of the Thickness structure.");
            }

            var sizeValue = (Thickness)value;
            var sizeParameter = (Thickness)parameter;
            var result = new Thickness(sizeValue.Left + sizeParameter.Left, sizeValue.Top + sizeParameter.Top, sizeValue.Right + sizeParameter.Right, sizeValue.Bottom + sizeParameter.Bottom);
            return result;
        }

        /// <inheritdoc/>
        [NotNull]
        public override object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (!(value is Thickness))
            {
                throw new ArgumentException("The value of the ConvertBack method of this converter must be a an instance of the Thickness structure.");
            }
            if (!(parameter is Thickness))
            {

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