dotnet/wpf · error · InvalidOperationException

SR.Enumerator_NotStarted

Error message

SR.Enumerator_NotStarted

What it means

Point3DCollection's enumerator Current property throws InvalidOperationException(SR.Enumerator_NotStarted) when Current is accessed before the first MoveNext() call (_index == -1). WPF generated enumerators only allow Current reads while positioned on a valid element.

Solutions

  1. Call MoveNext() before reading Current
  2. Use foreach, which guarantees MoveNext precedes Current access
  3. Guard with a bool flag tracking whether MoveNext has succeeded

Example fix

// before
var e = collection.GetEnumerator();
Console.WriteLine(e.Current); // throws
// after
var e = collection.GetEnumerator();
if (e.MoveNext()) Console.WriteLine(e.Current);
Defensive patterns

Strategy: type-guard

Validate before calling

bool canRead = enumeratorStarted; // true only after a MoveNext() returned true

Type guard

bool TryReadCurrent(System.Collections.IEnumerator e, out object? cur) { cur = null; if (e.MoveNext()) { cur = e.Current; return true; } return false; }

Try / catch

try { var cur = e.Current; }
catch (InvalidOperationException) { /* MoveNext not called yet; call MoveNext first */ }

Prevention

When it happens

Trigger: Reading e.Current immediately after GetEnumerator() without calling MoveNext(); reading Current in a while loop body before the first MoveNext returns true.

Common situations: Hand-written enumerator loops that inspect Current before advancing; refactorings that moved a Current read outside the loop condition.

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/3d47fb28119f2178. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media3D/Generated/Point3DCollection.cs:868

            /// <summary>
            /// Current element
            ///
            /// The behavior of IEnumerable&lt;T>.Current is undefined
            /// before the first MoveNext and after we have walked
            /// off the end of the list. However, the IEnumerable.Current
            /// contract requires that we throw exceptions
            /// </summary>
            public Point3D Current
            {
                get
                {
                    if (_index > -1)
                    {
                        return _current;
                    }
                    else if (_index == -1)
                    {
                        throw new InvalidOperationException(SR.Enumerator_NotStarted);
                    }
                    else
                    {
                        Debug.Assert(_index == -2, "expected -2, got " + _index + "\n");
                        throw new InvalidOperationException(SR.Enumerator_ReachedEnd);
                    }
                }
            }

            #endregion

            #region Data
            private Point3D _current;
            private Point3DCollection _list;
            private uint _version;
            private int _index;
            #endregion
        }

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