dotnet/wpf · error · NotSupportedException

Cannot convert from type.

Error message

Cannot convert from type.

What it means

ColorTypeConverter.ConvertFrom only supports the source types it recognizes (via IsSupportedType). Passing a value whose type is not supported throws NotSupportedException with the message 'Cannot convert from type.' The converter is intentionally minimal for XPS serialization.

Solutions

1. Use ColorConverter (System.Windows.Media) instead of ColorTypeConverter to parse color strings.
2. Only pass types accepted by IsSupportedType to ConvertFrom.
3. Parse colors manually with ColorConverter.ConvertFromString.
4. Catch NotSupportedException and fall back to a real color parser.

Example fix

// before
var color = (Color)new ColorTypeConverter().ConvertFromString("#FF0000");
// after
var color = (Color)ColorConverter.ConvertFromString("#FF0000");

if (value == null || !value.GetType().IsInstanceOfType(typeof(Color))) // verify supported input before ConvertFrom
colorTypeConverter.ConvertFrom(null, null, value);

static bool CanConvertFrom(object v) => v is Color;

try { return converter.ConvertFrom(context, culture, value); }
catch (NotSupportedException) { return ColorConverter.ConvertFromString(value.ToString()); }

When it happens

Trigger: Calling TypeConverter.ConvertFrom on ColorTypeConverter with a string or other type it does not list in IsSupportedType.

Common situations: Using ColorTypeConverter as a general-purpose Color parser in XAML or data binding; expecting ConvertFrom to parse hex color strings.

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

• Cannot convert to type.
• Cannot convert to type.
• SR.Converter_ConvertToNotSupported
• SR.Converter_ConvertToNotSupported
• ArgumentNullException (nameof(targetObject))

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/5121133376ce6772. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/ReachFramework/Serialization/ColorTypeConverter.cs:108

        /// <param name="value">
        /// The Object to convert.
        /// </param>
        /// <returns>
        /// An Object that represents the converted value.
        /// </returns>
        public
        override
        object
        ConvertFrom(
            ITypeDescriptorContext              context,
            System.Globalization.CultureInfo    culture,
            object                              value
            )
        {
            ArgumentNullException.ThrowIfNull(value);
            if (!IsSupportedType(value.GetType()))
            {
                throw new NotSupportedException(SR.Converter_ConvertFromNotSupported);
            }

            throw new NotImplementedException();
        }

        /// <summary>
        /// Converts the given value object to the specified type,
        /// using the arguments.
        /// </summary>
        /// <param name="context">
        /// An ITypeDescriptorContext that provides a format context.
        /// </param>
        /// <param name="culture">
        /// A CultureInfo object. If null is passed, the current
        /// culture is assumed.
        /// </param>
        /// <param name="value">
        /// The Object to convert.

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