dotnet/wpf · error · ArgumentException

SR.Format(SR.General_BadType, "ConvertFrom")

Error message

SR.Format(SR.General_BadType, "ConvertFrom")

What it means

TextDecorationCollectionConverter.ConvertFrom throws an ArgumentException (SR.General_BadType for "ConvertFrom") when the input object is neither null nor a string. The converter only supports string input (or null, which produces a different GetConvertFromException).

Solutions

  1. Pass a string like "underline" or "strikethrough,overline" to the converter.
  2. If you already have a TextDecorationCollection, use it directly instead of converting.
  3. Use ConvertFromString rather than ConvertFrom for string sources.

Example fix

// before
converter.ConvertFrom(context, culture, new object[] { "underline" });
// after
converter.ConvertFrom(context, culture, "underline");
Defensive patterns

Strategy: type-guard

Validate before calling

if (input is not string s) throw new ArgumentException("TextDecorationCollectionConverter accepts only string input", nameof(input));

Type guard

bool IsConvertibleToString(object? v) => v is string;

Try / catch

try { result = converter.ConvertFrom(context, culture, input); } catch (ArgumentException) { /* handle non-string input */ }

Prevention

When it happens

Trigger: Passing a non-string (e.g. an array, int, or TextDecorationCollection itself) to ConvertFrom / TypeDescriptor.ConvertFrom on TextDecorationCollectionConverter.

Common situations: XAML or designer value conversion pipelines feeding raw objects; reflection-based conversion helpers assuming broader input support.

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 dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/58d4e38cfffcc1ca. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/TextDecorationCollectionConverter.cs:59

        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
        {
            return sourceType == typeof(string);
        }

        /// <summary>
        /// Converts <paramref name="input"/> of <see langword="string"/> type to its <see cref="TextDecorationCollection"/> representation.
        /// </summary>
        /// <param name="context">Context information used for conversion, ignored currently.</param>
        /// <param name="culture">The culture specifier to use, ignored currently.</param>        
        /// <param name="input">The string to convert from.</param>
        /// <returns>A <see cref="TextDecorationCollection"/> representing the <see langword="string"/> specified by <paramref name="input"/>.</returns>
        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object input)
        {
            if (input is null)
                throw GetConvertFromException(input);

            if (input is not string value)
                throw new ArgumentException(SR.Format(SR.General_BadType, "ConvertFrom"), nameof(input));

            return ConvertFromString(value);
        }

        /// <summary>
        /// Converts <paramref name="text"/> to its <see cref="TextDecorationCollection"/> representation.
        /// </summary>
        /// <param name="text">The string to be converted into TextDecorationCollection object.</param>
        /// <returns>A <see cref="TextDecorationCollection"/> representing the <see cref="string"/> specified by <paramref name="text"/>.</returns>
        /// <remarks>
        /// The text parameter can be either be <see langword="null"/>; <see cref="string.Empty"/>; the string "None"
        /// or a combination of the predefined <see cref="TextDecorations"/> names delimited by commas (,).
        /// One or more blanks spaces can precede  or follow each text decoration name or comma.
        /// There can't be duplicate TextDecoration names in the string. The operation is case-insensitive. 
        /// </remarks>
        public static new TextDecorationCollection ConvertFromString(string text)
        {
            if (text is null)

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