dotnet/wpf · error · ArgumentException

SR.PropertyOfClassMustBeGreaterThanZero…

Error message

SR.PropertyOfClassMustBeGreaterThanZero (FontRenderingEmSize, TextRunProperties)

What it means

FetchTextRun requires FontRenderingEmSize to be strictly positive. It throws ArgumentException(SR.PropertyOfClassMustBeGreaterThanZero with FontRenderingEmSize/TextRunProperties) when the em size is zero or negative, since font size must be a positive real value to measure text.

Solutions

  1. Set FontRenderingEmSize to a positive value (e.g. > 0, at least 0.1) in your TextRunProperties
  2. Clamp computed font sizes to a small positive minimum before creating runs
  3. Validate run properties in your TextSource before returning the run

Example fix

// before
props.FontRenderingEmSize = fontSize; // fontSize may be 0
// after
props.FontRenderingEmSize = Math.Max(fontSize, 0.1);
Defensive patterns

Strategy: validation

Validate before calling

if (run.Properties == null || run.Properties.FontRenderingEmSize <= 0) throw new ArgumentException("FontRenderingEmSize must be > 0");

Type guard

bool HasValidEmSize(TextRun r) => r?.Properties?.FontRenderingEmSize > 0;

Try / catch

try { formatter.FormatLine(...); } catch (ArgumentException) { /* clamp em size and retry */ }

Prevention

When it happens

Trigger: TextRun.Properties.FontRenderingEmSize <= 0 returned by a TextSource; font size computed from data (e.g. zoom/scale) that collapsed to 0 or became negative.

Common situations: Zoom or scale factor of 0 applied to font size; uninitialized font size field defaulting to 0; data-binding producing NaN/0 sizes.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/3ec9fd7f87843852. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/TextFormatting/TextRunCacheImp.cs:118

            if(textRun == null)
            {
                // run not already cached, fetch new run and cache it

                textRun = settings.TextSource.GetTextRun(cpFetch);

                ArgumentOutOfRangeException.ThrowIfNegativeOrZero(textRun.Length, "textRun.Length");

                Plsrun plsrun = TextRunInfo.GetRunType(textRun);

                if (plsrun == Plsrun.Text || plsrun == Plsrun.InlineObject)
                {
                    TextRunProperties properties = textRun.Properties;

                    if (properties == null)
                        throw new ArgumentException(SR.TextRunPropertiesCannotBeNull);

                    if (properties.FontRenderingEmSize <= 0)
                        throw new ArgumentException(SR.Format(SR.PropertyOfClassMustBeGreaterThanZero, "FontRenderingEmSize", "TextRunProperties"));

                    double realMaxFontRenderingEmSize = Constants.RealInfiniteWidth / Constants.GreatestMutiplierOfEm;

                    if (properties.FontRenderingEmSize > realMaxFontRenderingEmSize)
                        throw new ArgumentException(SR.Format(SR.PropertyOfClassCannotBeGreaterThan, "FontRenderingEmSize", "TextRunProperties", realMaxFontRenderingEmSize));

                    CultureInfo culture = CultureMapper.GetSpecificCulture(properties.CultureInfo);

                    if (culture == null)
                        throw new ArgumentException(SR.Format(SR.PropertyOfClassCannotBeNull, "CultureInfo", "TextRunProperties"));

                    if (properties.Typeface == null)
                        throw new ArgumentException(SR.Format(SR.PropertyOfClassCannotBeNull, "Typeface", "TextRunProperties"));
                }


                //
                // TextRun is specifial to SpanVector because TextRun also encodes position which needs to be

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