dotnet/wpf · error · InvalidOperationException

SR.Enumerator_VerifyContext

Error message

SR.Enumerator_VerifyContext

What it means

The CharacterMetricsDictionary Enumerator's GetCurrentEntry throws this InvalidOperationException when Entry or Current is accessed before the enumerator has successfully advanced to a valid element (MoveNext was never called or returned false). SR.Enumerator_VerifyContext means there is no current entry to return.

Solutions

  1. Call MoveNext() and check it returns true before reading Entry/Current
  2. Guard the Entry access with a check that enumeration has started and is positioned on a valid element
  3. Handle empty dictionaries explicitly before enumerating

Example fix

// before
 var e = ((IDictionary)dict).GetEnumerator();
 var entry = ((IDictionaryEnumerator)e).Entry;
// after
 var e = ((IDictionary)dict).GetEnumerator();
 if (e.MoveNext()) { var entry = ((IDictionaryEnumerator)e).Entry; }
Defensive patterns

Strategy: try-catch

Validate before calling

bool CanReadEntry(IEnumerator e) => e is IDictionaryEnumerator de && /* enumeration started and positioned */ de.MoveNextCalled(); // track MoveNext yourself

Try / catch

try { var entry = ((IDictionaryEnumerator)enumerator).Entry; } catch (InvalidOperationException) { /* enumerator not positioned; call MoveNext first */ }

Prevention

When it happens

Trigger: Accessing IDictionaryEnumerator.Entry, Entry.Key/Value, or the KeyValuePair Current immediately after GetEnumerator(), after Reset(), or after MoveNext() returned false (end of collection or empty dictionary).

Common situations: Enumerating an empty CharacterMetricsDictionary and reading Current unconditionally; manual enumerator loops that read Entry before the first MoveNext; iterators that use IDictionaryEnumerator.Entry without guarding.

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/88ce78b32a16c150. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/CharacterMetricsDictionary.cs:576

                    return new SC.DictionaryEntry(entry.Key, entry.Value);
                }
            }

            // Current property for generic enumerator.
            public KeyValuePair<int, CharacterMetrics> Current
            {
                get
                {
                    return new KeyValuePair<int, CharacterMetrics>(_unicodeScalar, _value);
                }
            }

            private KeyValuePair<int, CharacterMetrics> GetCurrentEntry()
            {
                if (_value != null)
                    return new KeyValuePair<int, CharacterMetrics>(_unicodeScalar, _value);
                else
                    throw new InvalidOperationException(SR.Enumerator_VerifyContext);
            }

            SC.DictionaryEntry SC.IDictionaryEnumerator.Entry
            {
                get
                {
                    KeyValuePair<int, CharacterMetrics> entry = GetCurrentEntry();
                    return new SC.DictionaryEntry(entry.Key, entry.Value);
                }
            }

            object SC.IDictionaryEnumerator.Key
            {
                get
                {
                    return GetCurrentEntry().Key;
                }
            }

View on GitHub (pinned to 81131a70a4)