dotnet/wpf · error · InvalidOperationException

SR.Enumerator_ReachedEnd

Error message

SR.Enumerator_ReachedEnd

What it means

Reading Current on a MatchingLanguageEnumerator after MoveNext() returned false, i.e. iteration has passed the last element. The enumerator throws InvalidOperationException because there is no current item to return.

Solutions

  1. Break out of the loop when MoveNext() returns false before touching Current
  2. Use foreach, which never reads Current past the end
  3. Reset or re-acquire the enumerator instead of continuing to advance it

Example fix

// before
while (true) { Process(e.Current); e.MoveNext(); } // throws at end
// after
while (e.MoveNext()) { Process(e.Current); }
Defensive patterns

Strategy: try-catch

Validate before calling

bool hasCurrent = e.MoveNext();
// only then read e.Current

Try / catch

try { var v = e.Current; } catch (InvalidOperationException) { /* past end */ }

Prevention

When it happens

Trigger: Calling Current after MoveNext() returned false; repeatedly reading Current in a loop that ignores MoveNext's return value; re-reading Current at the end of manual iteration.

Common situations: Manual while(true) loops over GetMatchingLanguages() without breaking on false; enumerators stored across iterations and advanced past the end.

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

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/073dedc50946aae3. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Markup/XmlLanguage.cs:523

            public void Reset()
            {
                _current = _start;
                _pastEnd = false;
                _atStart = true;
                _maxCultureDepth = XmlLanguage.MaxCultureDepth;
            }

            public XmlLanguage Current
            {
                get
                {
                    if (_atStart)
                    {
                        throw new InvalidOperationException(SR.Enumerator_NotStarted);
                    }
                    if (_pastEnd)
                    {
                        throw new InvalidOperationException(SR.Enumerator_ReachedEnd);
                    }
 
                    return _current;
                }
            }

            public bool MoveNext()
            {
                if (_atStart)
                {
                    _atStart = false;
                    return true;
                }
                else if (_current.IetfLanguageTag.Length == 0)
                {
                    _atStart = false;
                    _pastEnd = true;
                    return false;

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