HandyOrg/HandyControl · error · NotSupportedException

NotSupportedException

Error message

NotSupportedException

What it means

BorderClipConverter produces a clip geometry for border elements (returning DependencyProperty.UnsetValue for degenerate sizes) and is one-way; ConvertBack unconditionally throws NotSupportedException. Reverse conversion from clip geometry back to the source value is intentionally not provided.

Solutions

1. Set Binding Mode=OneWay on bindings using BorderClipConverter.
2. Write a custom converter with a real ConvertBack if you need two-way behavior.
3. Use the converter only on decorative clip properties, not on data properties.

Example fix

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

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

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 BorderClipConverter in a TwoWay/OneWayToSource binding, or calling ConvertBack directly; applying it on an editable control whose properties bind TwoWay by default.

Common situations: Styling TextBox/ComboBox templates with this clip converter and missing the OneWay mode; copying the converter usage between read-only and editable elements.

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/7b8275476f0aaa51. Report an issue: GitHub.

Appendix: source

Thrown at src/Shared/HandyControl_Shared/Tools/Converter/BorderClipConverter.cs:47

                        new ArcSegment(new Point(width - radius.BottomRight, height), new Size(radius.BottomRight, radius.BottomRight), 90, false, SweepDirection.Clockwise, false),
                        new LineSegment(new Point(radius.BottomLeft, height), false),
                        new ArcSegment(new Point(0, height - radius.BottomLeft), new Size(radius.BottomLeft, radius.BottomLeft), 90, false, SweepDirection.Clockwise, false),
                        new LineSegment(new Point(0, radius.TopLeft), false),
                        new ArcSegment(new Point(radius.TopLeft, 0), new Size(radius.TopLeft, radius.TopLeft), 90, false, SweepDirection.Clockwise, false),
                    }, false)
                }
            };
            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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