dotnet/wpf · error

SR.EnumeratorReachedEnd

Error message

SR.EnumeratorReachedEnd

What it means

The enumerator's Current property throws InvalidOperationException with SR.EnumeratorReachedEnd when Current is read after MoveNext returned false (index past the last element). Once iteration has finished there is no valid current element, so the sentinel check raises instead of returning a stale or null value.

Solutions

1. Only read Current when the preceding MoveNext() returned true
2. Call Reset() (or get a fresh enumerator) before iterating again
3. Capture the last item inside the loop instead of reading Current afterward

Example fix

// before
while (e.MoveNext()) { }
var last = e.Current;
// after
object last = null;
while (e.MoveNext()) { last = e.Current; }

object last = null; while (enumerator.MoveNext()) { last = enumerator.Current; } /* do not read enumerator.Current after the loop */

When it happens

Trigger: Continuing to read Current after MoveNext() returned false, e.g. a loop that reads Current unconditionally one extra time, or caching the enumerator and reading Current after a completed pass.

Common situations: while(true) loops with a broken termination check, reusing a finished enumerator for a 'last element' access, or LINQ operators applied to an already-exhausted enumerator reference.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• SR.EnumeratorNotStarted
• Collection_CopyTo_ArrayCannotBeMultidimensional
• Collection_CopyTo_ArrayCannotBeMultidimensional
• Collection_CopyTo_IndexGreaterThanOrEqualToArrayLength
• Collection_CopyTo_IndexGreaterThanOrEqualToArrayLength

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/474dd917583d8bb9. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/documents/ContentElementCollection.cs:347

                    _currentElement = _collection;
                    _index = _collection.Size;
                    return (false);
                }
            }

            public TItem Current
            {
                get
                {
                    if (_currentElement == _collection)
                    {
                        if (_index == -1)
                        {
                            throw new InvalidOperationException(SR.EnumeratorNotStarted);
                        }
                        else
                        {
                            throw new InvalidOperationException(SR.EnumeratorReachedEnd);
                        }
                    }
                    return (TItem)_currentElement;
                }
            }

            /// <summary>
            ///     <see cref="IEnumerator.Current"/>
            /// </summary>
            object IEnumerator.Current
            {
                get
                {
                    return this.Current;
                }
            }

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