dotnet/wpf · error · InvalidOperationException

SR.Enumerator_NotStarted

Error message

SR.Enumerator_NotStarted

What it means

Model3DCollection's enumerator Current property throws InvalidOperationException(SR.Enumerator_NotStarted) when accessed before the first MoveNext call (_index == -1). There is no valid 'current' element before iteration begins; accessing it early is a usage bug, not a data problem. (After the end, a different message, Enumerator_ReachedEnd, is thrown.)

Solutions

1. Always call MoveNext and check it returned true before reading Current.
2. Restructure to a foreach loop, which enforces correct Current access ordering.
3. If you need the first element without an enumerator, use collection[0] (after checking Count).

Example fix

// before
var e = collection.GetEnumerator();
var first = e.Current; // InvalidOperationException: not started
// after
var e = collection.GetEnumerator();
if (e.MoveNext()) { var first = e.Current; }

if (!e.MoveNext()) return; // no elements; only then read e.Current

bool HasCurrent(IEnumerator e) { try { return e.MoveNext(); } catch { return false; } }

try { var cur = e.Current; } catch (InvalidOperationException ex) when (ex.Message.Contains("NotStarted")) { /* MoveNext was not called yet */ }

When it happens

Trigger: Reading enumerator.Current (or hitting it via foreach codegen misuse / manual enumerator loops) before calling MoveNext at least once; calling Current again after Reset without advancing.

Common situations: Hand-written enumerator loops with Current accessed outside the MoveNext loop condition; helper functions taking IEnumerator and peeking Current up front; after Reset() the state returns to -1 so an immediate Current read throws again.

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.Enumerator_CollectionChanged
• SR.Enumerator_CollectionChanged
• SR.Enumerator_CollectionChanged
• Cannot pass multidimensional array to the CopyTo method on…
• DoubleKeyFrameCollection

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/8087086d2388d580. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media3D/Generated/Model3DCollection.cs:882

            /// <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 Model3D 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 Model3D _current;
            private Model3DCollection _list;
            private uint _version;
            private int _index;
            #endregion
        }

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