dotnet/wpf · error · ArgumentException

SR.Collection_CopyTo_IndexGreaterThanOrEqualToArrayLength

Error message

SR.Collection_CopyTo_IndexGreaterThanOrEqualToArrayLength

What it means

CharacterMetricsDictionary.CopyTo(KeyValuePair<int,CharacterMetrics>[] array, int index) validates the destination index. If index is greater than or equal to array.Length, no element can ever be written and an ArgumentException is thrown. (A null array or negative index fails earlier with different exceptions.)

Solutions

Pass an index strictly less than array.Length (and >= 0).
Ensure the array is large enough: index + Count <= array.Length.
Guard the call with `if (index < array.Length)` before invoking CopyTo.

Example fix

// before
dict.CopyTo(pairs, pairs.Length);
// after
if (pairs.Length > 0) dict.CopyTo(pairs, 0);

Defensive patterns

Strategy: validation

Validate before calling

if (array == null) throw new ArgumentNullException(nameof(array));
if (index < 0 || index >= array.Length)
    throw new ArgumentOutOfRangeException(nameof(index));

Try / catch

try { dict.CopyTo(array, index); }
catch (ArgumentException ex) { /* fix index/array sizing, retry */ }

Prevention

Assert index < array.Length before CopyTo.
Prefer copying into a right-sized array at index 0.
Beware empty arrays with any index.

When it happens

Trigger: Calling dictionary.CopyTo(array, index) where index >= array.Length, e.g. CopyTo(new KeyValuePair<int,CharacterMetrics>[10], 10) or CopyTo(someArray, someArray.Length).

Common situations: Computing a start index from a cursor that has advanced past the buffer; off-by-one when copying into the tail of a larger array; passing an empty array with index 0.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/bc0d346d9e24b506. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/CharacterMetricsDictionary.cs:121

        /// </summary>
        [CLSCompliant(false)]
        public bool Contains(KeyValuePair<int, CharacterMetrics> item)
        {
            return item.Value != null && item.Value.Equals(GetValue(item.Key));
        }

        /// <summary>
        /// Copies the contents of the collection to the specified array.
        /// </summary>
        [CLSCompliant(false)]
        public void CopyTo(KeyValuePair<int, CharacterMetrics>[] array, int index)
        {
            ArgumentNullException.ThrowIfNull(array);

            ArgumentOutOfRangeException.ThrowIfNegative(index);

            if (index >= array.Length)
                throw new ArgumentException(SR.Format(SR.Collection_CopyTo_IndexGreaterThanOrEqualToArrayLength, "index", "array"));

            CharacterMetrics[][] pageTable = _pageTable;
            if (pageTable != null)
            {
                int k = index;

                for (int i = 0; i < pageTable.Length; ++i)
                {
                    CharacterMetrics[] page = pageTable[i];
                    if (page != null)
                    {
                        for (int j = 0; j < page.Length; ++j)
                        {
                            CharacterMetrics metrics = page[j];
                            if (metrics != null)
                            {
                                if (k >= array.Length)
                                    throw new ArgumentException(SR.Format(SR.Collection_CopyTo_NumberOfElementsExceedsArrayLength, index, "array"));

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