dotnet/wpf · error · ArgumentException

SR.Collection_BadRank

Error message

SR.Collection_BadRank

What it means

PathSegmentCollection.CopyTo throws ArgumentException with SR.Collection_BadRank when the destination array is not one-dimensional (Rank != 1). CopyTo requires a single-dimensional Array because it writes elements by linear index.

Solutions

  1. Use a one-dimensional PathSegment[] as the destination.
  2. If you need 2D storage, copy into a flat 1D array first and then reshape manually.
  3. Check array.Rank == 1 before calling CopyTo and handle the multidimensional case separately.

Example fix

// before
var grid = new PathSegment[2, 5];
collection.CopyTo(grid, 0);
// after
var flat = new PathSegment[collection.Count];
collection.CopyTo(flat, 0);
Defensive patterns

Strategy: validation

Validate before calling

if (array == null) throw new ArgumentNullException(nameof(array));
if (array.Rank != 1) throw new ArgumentException("Destination array must be one-dimensional", nameof(array));
collection.CopyTo(array, index);

Type guard

bool IsFlatSegmentArray(Array a) => a is PathSegment[];

Try / catch

try
{
    collection.CopyTo(array, 0);
}
catch (ArgumentException)
{
    var flat = new PathSegment[collection.Count];
    collection.CopyTo(flat, 0);
}

Prevention

When it happens

Trigger: Calling pathSegmentCollection.CopyTo(array, index) where array was created with multiple dimensions, e.g. new PathSegment[2, 5].

Common situations: Reusing a multidimensional buffer across BCL interop code; generic copy helpers that accept Array and pass through whatever rank the caller supplied.

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/930de310536d27e1. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Generated/PathSegmentCollection.cs:402

        #endregion

        #region ICollection

        void ICollection.CopyTo(Array array, int index)
        {
            ReadPreamble();

            ArgumentNullException.ThrowIfNull(array);

            // This will not throw in the case that we are copying
            // from an empty collection.  This is consistent with the
            // BCL Collection implementations. (Windows 1587365)
            ArgumentOutOfRangeException.ThrowIfNegative(index);
            ArgumentOutOfRangeException.ThrowIfGreaterThan(index, array.Length - _collection.Count);

            if (array.Rank != 1)
            {
                throw new ArgumentException(SR.Collection_BadRank);
            }

            // Elsewhere in the collection we throw an AE when the type is
            // bad so we do it here as well to be consistent
            try
            {
                int count = _collection.Count;
                for (int i = 0; i < count; i++)
                {
                    array.SetValue(_collection[i], index + i);
                }
            }
            catch (InvalidCastException e)
            {
                throw new ArgumentException(SR.Format(SR.Collection_BadDestArray, this.GetType().Name), e);
            }
        }

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