dotnet/wpf · error · ArgumentException

SR.Format(SR.TextElementCollection_CannotCopyToArrayNotSuffi…

Error message

SR.Format(SR.TextElementCollection_CannotCopyToArrayNotSufficientMemory, count, arrayIndex, array.Length)

What it means

CopyTo throws ArgumentException (TextElementCollection_CannotCopyToArrayNotSufficientMemory) when the target array is too small: array.Length < arrayIndex + count, where count is the number of elements in the collection. The copy loop would write past the end of the array, so it is rejected before any element is copied.

Solutions

1. Size the array to list.Count plus the offset: new TextElementType[list.Count + arrayIndex].
2. Call list.Count right before CopyTo rather than using a stale count.
3. Use list.ToArray<T>() which allocates the exact size.
4. Catch ArgumentException and retry with an array of Count + arrayIndex elements.

Example fix

// before
var arr = new Paragraph[oldCount];
list.CopyTo(arr, 0);
// after
var arr = new Paragraph[list.Count];
list.CopyTo(arr, 0);

if (array.Length - arrayIndex < list.Count) { array = new TextElementType[list.Count + arrayIndex]; }

try { list.CopyTo(arr, offset); } catch (ArgumentException) { arr = new TextElementType[list.Count + offset]; list.CopyTo(arr, offset); }

When it happens

Trigger: Calling CopyTo(array, arrayIndex) where array.Length - arrayIndex is less than the collection's Count.

Common situations: Reusing a cached array after the document grew (more paragraphs added); reserving only part of a larger buffer but forgetting the offset consumes space; copying between documents of different sizes.

Related errors

• array
• Cannot pass multidimensional array to the CopyTo method on…
• SR.Argument_InvalidOffLen
• SR.Collection_BadRank
• " }} " element found. Expected fixed page element ( }} ).

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/f74d74d8bf403b1f. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/TextElementCollection.cs:614

            ArgumentNullException.ThrowIfNull(array);

            Type elementType = array.GetType().GetElementType();
            if (elementType == null || !elementType.IsAssignableFrom(typeof(TextElementType)))
            {
                throw new ArgumentException("array");
            }

            ArgumentOutOfRangeException.ThrowIfNegative(arrayIndex);

            if (arrayIndex > array.Length)
            {
                throw new ArgumentException("arrayIndex");
            }

            if (array.Length < arrayIndex + count)
            {
                throw new ArgumentException(SR.Format(SR.TextElementCollection_CannotCopyToArrayNotSufficientMemory, count, arrayIndex, array.Length));
            }

            for (TextElementType element = (TextElementType)this.FirstChild; element != null; element = (TextElementType)element.NextElement)
            {
                array.SetValue(element, arrayIndex++);
            }
        }

        int ICollection.Count
        {
            get 
            {
                return this.Count;
            }
        }

        bool ICollection.IsSynchronized
        {

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