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

NumericToThickness.ConvertBack requires both the value and the parameter to be WPF Thickness instances because it multiplies each thickness component by a scalar derived from the parameter. The library throws ArgumentException to fail fast when a caller passes a value or parameter of any other type instead of silently producing a wrong thickness.

Solutions

Pass a System.Windows.Thickness instance (or a Thickness that the XAML parser creates, e.g. '2') as ConverterParameter in the ConvertBack path.
Ensure the value passed to ConvertBack is also a Thickness; convert scalars on the value side instead.
If the binding is one-way, switch to OneWayValueConverter-style usage so ConvertBack is never invoked.

Example fix

// before
binding.ConverterParameter = 2.0; // double -> throws
// after
binding.ConverterParameter = new System.Windows.Thickness(2);

Defensive patterns

Strategy: type-guard

Validate before calling

bool ok = value is System.Windows.Thickness && parameter is System.Windows.Thickness;

Type guard

static bool IsThicknessPair(object value, object parameter) => value is System.Windows.Thickness && parameter is System.Windows.Thickness;

Try / catch

try { return converter.ConvertBack(value, targetType, parameter, culture); }
catch (ArgumentException ex) { /* log ex.ParamName, fall back to original value */ return value; }

Prevention

Always pass a Thickness as ConverterParameter for this converter
Use Thickness resources or constructor calls in XAML rather than bare numbers
Keep two-way and one-way converters in separate instances/resources

When it happens

Trigger: Calling NumericToThickness.ConvertBack(value, targetType, parameter, culture) where parameter (or value) is not a System.Windows.Thickness — e.g. passing a double, a string, a custom thickness-like struct, or a binding producing null.

Common situations: Wiring the same converter instance in both directions of a TwoWay binding without realizing ConvertBack demands a Thickness parameter; passing ConverterParameter='2.0' instead of a Thickness; copying usage from a similar converter like SumSize that expects Size.

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/834c29569677c0a3. Report an issue: GitHub.

Appendix: source

Thrown at sources/presentation/Stride.Core.Presentation.Wpf/ValueConverters/NumericToThickness.cs:53

            {
                throw new ArgumentException("The parameter of this converter must be an instance of the Thickness structure. Use {sd:Thickness (arguments)} to construct one.");
            }

            var thickness = (Thickness)parameter;
            var result = new Thickness(thickness.Left * scalar, thickness.Top * scalar, thickness.Right * scalar, thickness.Bottom * scalar);
            return result;
        }

        /// <inheritdoc/>
        public override object ConvertBack(object value, [NotNull] 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 thicknessValue = (Thickness)value;
            var thicknessParameter = (Thickness)parameter;

            var scalar = 0.0;
            if (Math.Abs(thicknessParameter.Left) > double.Epsilon)
            {
                scalar = thicknessValue.Left / thicknessParameter.Left;
            }
            else if (Math.Abs(thicknessParameter.Right) > double.Epsilon)
            {
                scalar = thicknessValue.Right / thicknessParameter.Right;
            }
            else if (Math.Abs(thicknessParameter.Top) > double.Epsilon)
            {
                scalar = thicknessValue.Top / thicknessParameter.Top;
            }
            else if (Math.Abs(thicknessParameter.Bottom) > double.Epsilon)

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