AvaloniaUI/Avalonia · error · InvalidDataException

Invalid double value

Error message

Invalid double value

What it means

Thrown by ReadDouble when ReadArgument could not extract a valid numeric token from the span. ReadArgument validates an optional leading '-', integer digits, an optional '.', fractional digits, and optional scientific notation; if none of those form a valid number, ReadArgument returns false and ReadDouble throws. This affects every numeric coordinate, size, and angle in the path.

Source

Thrown at src/Avalonia.Base/Media/PathMarkupParser.cs:561

            
            span = span.Slice(1);
            
            switch (c)
            {
                case '0':
                    return false;
                case '1':
                    return true;
                default:
                    throw new InvalidDataException("Invalid bool rule");
            }
        }

        private static double ReadDouble(ref ReadOnlySpan<char> span)
        {
            if (!ReadArgument(ref span, out var doubleValue))
            {
                throw new InvalidDataException("Invalid double value");
            }

            return double.Parse(doubleValue.ToString(), CultureInfo.InvariantCulture);
        }

        private static Size ReadSize(ref ReadOnlySpan<char> span)
        {
            var width = ReadDouble(ref span);
            span = ReadSeparator(span);
            var height = ReadDouble(ref span);
            return new Size(width, height);
        }

        private static Point ReadPoint(ref ReadOnlySpan<char> span)
        {
            var x = ReadDouble(ref span);
            span = ReadSeparator(span);
            var y = ReadDouble(ref span);

View on GitHub (pinned to 11c5427268)

Solutions

1. Ensure every numeric argument is a well-formed number using '.' as the decimal separator and invariant culture.
2. Remove trailing separators and empty tokens from the path string.
3. If you use ',' as a decimal separator in your locale, convert to '.' (and use ' ' or ',' as the coordinate separator per SVG path grammar) before parsing.

Example fix

// before (locale comma as decimal, plus stray comma)
geometry.Parse("M0,0 L10,5,5,0");

// after
geometry.Parse("M0,0 L10,5 5,0");

static bool AllNumbersWellFormed(string path)
{
    // split on command letters/separators and double.TryParse each token
    // with CultureInfo.InvariantCulture; reject empties/non-numbers.
    return true;
}

try { parser.Parse(data); }
catch (InvalidDataException ex) when (ex.Message == "Invalid double value")
{ /* report which numeric token is malformed */ }

When it happens

Trigger: Any command whose numeric argument is missing, empty, or non-numeric, e.g. 'M x,y' (letters), 'L' followed by end of string, 'H,' (comma with no number), or 'C1,1,1,1,' (trailing separator with no value).

Common situations: Truncated path strings; stray commas/semicolons instead of expected numbers; localized number formatting using ',' as decimal separator bleeding into a comma-separated coordinate list; copy-paste dropping digits.

Related errors

• Invalid fill rule.
• Invalid fill rule
• Invalid bool rule.
• Invalid bool rule
• Unexpected path command '{c}'.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/a842f8b1c709ffc7. Report an issue: GitHub.