HandyOrg/HandyControl · error · NotSupportedException

NotSupportedException

Error message

NotSupportedException

What it means

BorderCircularClipConverter converts size/border data into a circular clip geometry and is one-way only; its ConvertBack unconditionally throws NotSupportedException. The library provides no reverse mapping from clip geometry back to the bound source values.

Solutions

1. Set Binding Mode=OneWay on the binding that uses this converter.
2. Write a custom converter with your own ConvertBack if reverse conversion is genuinely needed.
3. Move the binding source to a read-only property so WPF never invokes ConvertBack.

Example fix

// before
{Binding ActualWidth, Converter={StaticResource BorderCircularClipConverter}}
// after
{Binding ActualWidth, Mode=OneWay, Converter={StaticResource BorderCircularClipConverter}}

bool usesConverterBack = binding.Mode == BindingMode.TwoWay || binding.Mode == BindingMode.OneWayToSource;
if (usesConverterBack && converter is BorderCircularClipConverter) throw new InvalidOperationException("Use Mode=OneWay with BorderCircularClipConverter");

static bool IsOneWay(BindingBase b) => b is Binding bd && bd.Mode == BindingMode.OneWay;

try { var result = converter.ConvertBack(value, targetTypes, parameter, culture); } catch (NotSupportedException) { return Array.Empty<object>(); // one-way converter
}

When it happens

Trigger: Using BorderCircularClipConverter in a TwoWay/OneWayToSource binding or calling ConvertBack directly; binding an element's Clip/Geometry property with this converter in an editable control.

Common situations: Applying the converter in a control template where the binding defaults to TwoWay; copying a binding from another converter and forgetting the mode.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• NotSupportedException
• NotSupportedException
• NotSupportedException
• Specified type ' ' is not supported.
• Can't call EndInit without first calling BeginInit.

AI-assisted analysis of HandyOrg/HandyControl@2c0875ebd6 (2026-09-14). Data as JSON: /api/errors/b9533727d70a27bf. Report an issue: GitHub.

Appendix: source

Thrown at src/Shared/HandyControl_Shared/Tools/Converter/BorderCircularClipConverter.cs:33

        if (values.Length == 3 && values[0] is double width && values[1] is double height && values[2] is CornerRadius radius)
        {
            if (width < double.Epsilon || height < double.Epsilon)
            {
                return Geometry.Empty;
            }

            var clip = new RectangleGeometry(new Rect(0, 0, width, height), radius.TopLeft, radius.TopLeft);
            clip.Freeze();

            return clip;
        }

        return DependencyProperty.UnsetValue;
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}

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