AvaloniaUI/Avalonia · error · FormatException

Invalid text trimming string: '{s}'.

Error message

Invalid text trimming string: '{s}'.

What it means

Thrown by TextTrimming.Parse when the input string does not match any known text-trimming mode. Avalonia recognizes the named enum values None, CharacterEllipsis, WordEllipsis, PrefixCharacterEllipsis, and PathSegmentEllipsis (matched by name). Any other string is treated as a malformed trimming specification and rejected with a FormatException.

Source

Thrown at src/Avalonia.Base/Media/TextTrimming.cs:85

            }
            if (Matches(nameof(CharacterEllipsis)))
            {
                return CharacterEllipsis;
            }
            else if (Matches(nameof(WordEllipsis)))
            {
                return WordEllipsis;
            }
            else if (Matches(nameof(PrefixCharacterEllipsis)))
            {
                return PrefixCharacterEllipsis;
            }
            else if (Matches(nameof(PathSegmentEllipsis)))
            {
                return PathSegmentEllipsis;
            }

            throw new FormatException($"Invalid text trimming string: '{s}'.");
        }
    }
}

View on GitHub (pinned to 11c5427268)

Solutions

1. Use one of the exact recognized names: None, CharacterEllipsis, WordEllipsis, PrefixCharacterEllipsis, or PathSegmentEllipsis.
2. Trim whitespace and verify the value against the known set before calling Parse.
3. If the value comes from external input, validate it first or wrap Parse in a try/catch and fall back to a default trimming mode.

Example fix

// before
var trimming = TextTrimming.Parse("WordElipsis"); // typo, throws

// after
var trimming = TextTrimming.Parse("WordEllipsis");

static readonly HashSet<string> s_knownTrimmings = new(StringComparer.OrdinalIgnoreCase)
{
    "None", "CharacterEllipsis", "WordEllipsis", "PrefixCharacterEllipsis", "PathSegmentEllipsis"
};

static TextTrimming SafeParseTrimming(string s)
    => s != null && s_knownTrimmings.Contains(s.Trim())
        ? TextTrimming.Parse(s)
        : TextTrimming.WordEllipsis;

try { return TextTrimming.Parse(input); }
catch (FormatException) { return TextTrimming.WordEllipsis; }

When it happens

Trigger: Calling TextTrimming.Parse with a string that is not one of the recognized enum names (case-insensitive match via the Matches helper). For example a typo like 'WordEllipsis ' with stray whitespace, or a value loaded from config/XAML that does not correspond to a TextTrimming mode.

Common situations: Deserializing a TextTrimming from user config, JSON, or a CSS-like string where the value is misspelled or uses a different casing not handled; version mismatches where an older codebase references a trimming name that was renamed or removed; copy-paste of WPF-only values that Avalonia does not support.

Related errors

• Invalid transform string: '{s}'.
• Too many provided values.
• Invalid value {value.Value} {unitString} for {function}
• Invalid format. {function} expects {count} value(s).
• Invalid unit: {part.ToString()}

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/97a76d82a64c1afd. Report an issue: GitHub.