AvaloniaUI/Avalonia · error · ArgumentException

Could not parse text decoration.

Error message

Could not parse text decoration.

What it means

Thrown by GetTextDecorationLocation when SpanHelpers.TryParseEnum<TextDecorationLocation> fails for a token. The token must match a TextDecorationLocation enum name (case-insensitive, e.g. Baseline, OverLine, Strikethrough, Underline). Any unrecognized word, abbreviation, or stray character fails the parse.

Source

Thrown at src/Avalonia.Base/Media/TextDecorationCollection.cs:69

                textDecorations.Add(new TextDecoration { Location = textDecorationLocation });
            }

            return textDecorations;
        }

        /// <summary>
        /// Parses a <see cref="TextDecorationLocation"/> string.
        /// </summary>
        /// <param name="s">The string.</param>
        /// <returns>The <see cref="TextDecorationLocation"/>.</returns>
        private static TextDecorationLocation GetTextDecorationLocation(ReadOnlySpan<char> s)
        {
            if (SpanHelpers.TryParseEnum<TextDecorationLocation>(s,true, out var location))
            {
                return location;
            }

            throw new ArgumentException("Could not parse text decoration.", nameof(s));
        }
    }
}

View on GitHub (pinned to 11c5427268)

Solutions

1. Use the exact TextDecorationLocation enum names: Baseline, OverLine, Strikethrough, Underline (case-insensitive).
2. Map CSS names before parsing: 'line-through' -> 'Strikethrough', 'overline' -> 'OverLine'.
3. Trim whitespace and validate each token against Enum.GetNames<TextDecorationLocation>() before composing the string.

Example fix

// before
var d = TextDecorationCollection.Parse("line-through,underline");

// after
var d = TextDecorationCollection.Parse("Strikethrough,Underline");

static readonly HashSet<string> Valid =
    new(Enum.GetNames<TextDecorationLocation>(), StringComparer.OrdinalIgnoreCase);
static bool IsValidDecoration(string tok) => Valid.Contains(tok.Trim());

static bool IsValidDecorationName(string s) =>
    Enum.GetNames<TextDecorationLocation>().Any(n =>
        n.Equals(s, StringComparison.OrdinalIgnoreCase));

try { var d = TextDecorationCollection.Parse(s); }
catch (ArgumentException ex) when (ex.Message.Contains("Could not parse"))
{ /* map CSS names or report invalid token */ }

When it happens

Trigger: Strings like 'underline2', 'italic' (not a decoration), 'line-through' (the CSS name, not the enum name), or a typo like 'Underlin'.

Common situations: Mapping CSS text-decoration values directly (CSS uses 'line-through' where Avalonia uses 'Strikethrough'); user-typed decoration names; abbreviations or localized names.

Related errors

• Text decoration already specified.
• Invalid value
• Invalid fill rule.
• Invalid fill rule
• Invalid bool rule.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/201f549db6f50743. Report an issue: GitHub.