AvaloniaUI/Avalonia · error · FormatException

Invalid CornerRadius.

Error message

Invalid CornerRadius.

What it means

Thrown as FormatException by CornerRadius.Parse(string) when the input string cannot be tokenized into 1–4 double values (uniform, top-left/bottom-right, or four-corner). Parse uses an invariant-culture SpanStringTokenizer and the message 'Invalid CornerRadius.' is the constant exceptionMessage.

Source

Thrown at src/Avalonia.Base/CornerRadius.cs:114

            using (var tokenizer = new SpanStringTokenizer(s, CultureInfo.InvariantCulture, exceptionMessage))
            {
                if (tokenizer.TryReadDouble(out var a))
                {
                    if (tokenizer.TryReadDouble(out var b))
                    {
                        if (tokenizer.TryReadDouble(out var c))
                        {
                            return new CornerRadius(a, b, c, tokenizer.ReadDouble());
                        }

                        return new CornerRadius(a, b);
                    }

                    return new CornerRadius(a);
                }

                throw new FormatException(exceptionMessage);
            }
        }

        public static bool operator ==(CornerRadius left, CornerRadius right)
        {
            return left.Equals(right);
        }

        public static bool operator !=(CornerRadius left, CornerRadius right)
        {
            return !(left == right);
        }
    }
}

View on GitHub (pinned to 11c5427268)

Solutions

1. Provide a valid CornerRadius string: one value ("5"), two ("5,10"), or four ("5,10,5,10") doubles separated by commas or spaces, using invariant period decimals.
2. If the source is locale-dependent, normalize/replace separators before parsing or use the CornerRadius(double) constructors directly.
3. Validate with double.TryParse on each token before calling Parse, or wrap Parse in try/catch FormatException.

Example fix

// before
var c = CornerRadius.Parse("1;2"); // throws
// after
var c = CornerRadius.Parse("1,2"); // or new CornerRadius(1, 2)

if (!CornerRadius.TryParseInvariant(s, out var corner))
    throw new FormatException($"Invalid CornerRadius: '{s}'");

try { var c = CornerRadius.Parse(s); }
catch (FormatException) { c = default; // or log }

When it happens

Trigger: Calling CornerRadius.Parse(s) where s is empty, contains non-numeric text, has too many tokens, or uses the wrong decimal separator for invariant culture (e.g., a comma where a period is expected, or locale-specific formatting). Also thrown when the first token read fails entirely (line 114).

Common situations: XAML or code passes a malformed CornerRadius string like "abc", "1,,2", "1;2", or a locale-formatted value using comma decimals. Binding a CornerRadius from a string source with wrong formatting. Deserialization of CornerRadius from user input.

Related errors

• Not supported format
• No Setter property assigned.
• 'name' may not contain periods.
• Could not convert '{s}' to {typeof(T)}.
• Bad format specifier.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/cd8aa7f99d7b053f. Report an issue: GitHub.