What causes "NotSupportedException" in HandyOrg/HandyControl?

Set the binding to Mode=OneWay when using this converter so ConvertBack is never invoked.

HandyOrg/HandyControl · error · NotSupportedException

NotSupportedException

Error message

NotSupportedException

What it means

BooleanArr2VisibilityConverter is a one-way converter: ConvertBack is intentionally unimplemented and always throws NotSupportedException. It converts a bool[] into Visibility for display only; converting a Visibility back into a bool array has no defined mapping in this library.

Solutions

Set the binding to Mode=OneWay when using this converter so ConvertBack is never invoked.
Swap to a different converter if you genuinely need two-way bool[]/Visibility conversion, writing your own ConvertBack.
Never call ConvertBack manually on this converter.

Example fix

// before
{Binding Flags, Converter={StaticResource BooleanArr2VisibilityConverter}} <!-- TwoWay on editable control -->
// after
{Binding Flags, Mode=OneWay, Converter={StaticResource BooleanArr2VisibilityConverter}}

Defensive patterns

Strategy: type-guard

Validate before calling

bool usesConverterBack = binding.Mode == BindingMode.TwoWay || binding.Mode == BindingMode.OneWayToSource;
if (usesConverterBack && converter is BooleanArr2VisibilityConverter) throw new InvalidOperationException("Use Mode=OneWay with BooleanArr2VisibilityConverter");

Type guard

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

Try / catch

try { var result = converter.ConvertBack(value, targetTypes, parameter, culture); } catch (NotSupportedException) { return Array.Empty<object>(); // one-way converter: no back conversion
}

Prevention

Set Mode=OneWay on every binding that uses BooleanArr2VisibilityConverter.
Avoid using this converter on editable controls (TextBox, CheckBox) whose defaults are TwoWay.
Write a custom two-way converter if reverse conversion is actually required.

When it happens

Trigger: Using BooleanArr2VisibilityConverter in a TwoWay or OneWayToSource binding, or calling ConvertBack directly; a binding that pushes target (Visibility) changes back to the source.

Common situations: Forgetting to set Binding Mode=OneWay (default for most controls is TwoWay on editable controls like CheckBox/ComboBox); reusing the converter in an editable control template.

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

AI-assisted analysis of HandyOrg/HandyControl@2c0875ebd6 (2026-09-14). Data as JSON: /api/errors/6f49f61b444a6152. Report an issue: GitHub.

Appendix: source

Thrown at src/Shared/HandyControl_Shared/Tools/Converter/BooleanArr2VisibilityConverter.cs:36

        var arr = new List<bool>();
        foreach (var item in values)
        {
            if (item is bool boolValue)
            {
                arr.Add(boolValue);
            }
            else
            {
                return Visibility.Collapsed;
            }
        }
        return arr.All(item => item) ? Visibility.Visible : Visibility.Collapsed;
    }

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

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