dotnet/wpf · error · ArgumentException

SR.CannotConvertStringToType

Error message

SR.CannotConvertStringToType

What it means

CharacterMetrics.ParseMetrics splits a semicolon-separated metrics string into fields and parses each as an invariant-culture double. When double.TryParse fails for a required field, it throws ArgumentException with SR.CannotConvertStringToType naming the field and target type 'double'.

Solutions

  1. Correct the field to be an invariant-culture double (use '.' as decimal separator, optional leading sign).
  2. Re-export the metrics file with InvariantCulture formatting.
  3. Pre-validate each field with double.TryParse(s, NumberStyles.AllowDecimalPoint | AllowLeadingSign, CultureInfo.InvariantCulture, out _) before construction.

Example fix

// before
new CharacterMetrics("0,1,5;0,75;0;0;0;0;0"); // '1,5' not parseable invariantly

// after
new CharacterMetrics("0,1.5;0,75;0;0;0;0;0");
Defensive patterns

Strategy: validation

Validate before calling

static bool IsInvariantDouble(string s) =>
    double.TryParse(s, NumberStyles.AllowDecimalPoint | NumberStyles.AllowLeadingSign,
        System.Windows.Markup.TypeConverterHelper.InvariantEnglishUS, out _);

Try / catch

try { var m = new CharacterMetrics(str); }
catch (ArgumentException ex) when (ex.Message.Contains("double")) { Log($"Bad numeric field: {ex.Message}"); m = null; }

Prevention

When it happens

Trigger: A metrics string field containing non-numeric text, wrong decimal separator (e.g. ',' instead of '.'), or extra characters in a required field position.

Common situations: Locale-edited font metric files (comma decimal separators); truncated or concatenated fields shifting numeric values; whitespace or units ('px') inside numeric fields.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/74db471d6f8f3b9c. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/CharacterMetrics.cs:165

                    ++j;

                // Let k be end-of-field without trailing whitespace.
                int k = j;
                while (k > i && s[k - 1] == ' ')
                    --k;

                if (k > i)
                {
                    // Non-empty field; convert it to double.
                    ReadOnlySpan<char> field = s.AsSpan(i, k - i);
                    if (!double.TryParse(
                        field,
                        NumberStyles.AllowDecimalPoint | NumberStyles.AllowLeadingSign,
                        System.Windows.Markup.TypeConverterHelper.InvariantEnglishUS,
                        out metrics[fieldIndex]
                        ))
                    {
                        throw new ArgumentException(SR.Format(SR.CannotConvertStringToType, field.ToString(), "double"));
                    }
                }
                else if (fieldIndex < NumRequiredFields)
                {
                    // Empty field; make sure it's an optional one.
                    throw new ArgumentException(SR.CharacterMetrics_MissingRequiredField);
                }

                ++fieldIndex;

                if (j < s.Length)
                {
                    // There's a comma so check if we've exceeded the number of fields.
                    if (fieldIndex == NumFields)
                        throw new ArgumentException(SR.CharacterMetrics_TooManyFields);

                    // Initialize character index for next iteration.
                    i = j + 1;

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