dotnet/wpf · error · ArgumentException

SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo…

Error message

SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo, CodepointCount + 1)

What it means

When caretStops is supplied and non-empty, GlyphRun.Initialize requires caretStops.Count == CodepointCount + 1 (one stop per codepoint plus a trailing stop). Any other count is rejected with ArgumentException on the caretStops parameter.

Solutions

  1. Size caretStops to CodepointCount + 1 (count surrogate pairs as one codepoint)
  2. Pass null (or empty) caretStops if default caret behavior is acceptable
  3. Compute codepoint count with StringInfo.GetTextElementEnumerator / char.IsSurrogatePair logic

Example fix

// before
caretStops = new bool[chars.Length];
// after
caretStops = new bool[CodepointCount + 1]; // +1 for trailing stop
Defensive patterns

Strategy: validation

Validate before calling

if (caretStops != null && caretStops.Count != 0 && caretStops.Count != CodepointCount(characters) + 1)
    throw new ArgumentException("caretStops must have CodepointCount+1 entries");

Type guard

static bool CaretStopsValid(IList<bool> stops, int codepointCount) => stops == null || stops.Count == 0 || stops.Count == codepointCount + 1;

Try / catch

try { var run = new GlyphRun(...); }
catch (ArgumentException ex) when (ex.ParamName == "caretStops") { /* fix size or pass null */ }

Prevention

When it happens

Trigger: Calling the GlyphRun constructor, TryCreate, or EndInit with a caretStops collection whose length is not (number of codepoints + 1) — e.g. sizing it to characters.Count or glyphIndices.Count.

Common situations: Implementing custom caret navigation / hit-testing and miscomputing the caret stop array length, especially with surrogate pairs where codepoints differ from chars.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/5c6a4cfde4a97df4. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/GlyphRun.cs:411

                                throw new ArgumentException(SR.ClusterMapFirstEntryMustBeZero, nameof(clusterMap));
                            }
                        }
                        else
                        {
                            throw new ArgumentException(SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo, characters.Count), nameof(clusterMap));
                        }
                    }
                    else
                    {
                        if (GlyphCount != characters.Count)
                            throw new ArgumentException(SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo, GlyphCount), nameof(clusterMap));
                    }
                }

                if (caretStops != null && caretStops.Count != 0)
                {
                    if (caretStops.Count != CodepointCount + 1)
                        throw new ArgumentException(SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo, CodepointCount + 1), nameof(caretStops));
                }

                if (isSideways && (bidiLevel & 1) != 0)
                    throw new ArgumentException(SR.SidewaysRTLTextIsNotSupported);

                // NOTE:  In previous versions this function would estimate the size
                // of this glyph run's bitmaps and compare it against the theoretical
                // maximum size allowed before rendering falls back to using geometry.
                // This was done in order to produce a managed exception where we might
                // hit overflow or memory allocation issues in native code.
                // We no longer own the code the produces these bitmaps so we can't reliably
                // avoid the issue here any longer.
            }
            else
            {
                ArgumentOutOfRangeException.ThrowIfEqual(renderingEmSize, double.NaN);
                ArgumentOutOfRangeException.ThrowIfNegative(renderingEmSize);
                ArgumentNullException.ThrowIfNull(glyphTypeface);

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