What causes "SR.Enumerator_ReachedEnd" in dotnet/wpf?

Capture the current item in a local variable inside the loop instead of reading Current afterwards

dotnet/wpf · error · InvalidOperationException

SR.Enumerator_ReachedEnd

Error message

SR.Enumerator_ReachedEnd

What it means

Point3DCollection's enumerator Current property throws InvalidOperationException(SR.Enumerator_ReachedEnd) when Current is accessed after enumeration completed (MoveNext returned false, _index == -2). Same fail-fast contract as the BCL List<T> enumerator.

Solutions

Capture the current item in a local variable inside the loop instead of reading Current afterwards
Call Reset() (on an unmodified collection) before re-reading, or get a fresh enumerator
Restructure to use foreach with a variable holding the element of interest

Example fix

// before
Point3D last;
foreach (Point3D p in collection) { }
last = ((Point3DCollection.Enumerator)en).Current; // throws
// after
Point3D last = default;
foreach (Point3D p in collection) { last = p; }

Defensive patterns

Strategy: type-guard

Validate before calling

bool canRead = lastMoveNextReturnedTrue; // track MoveNext outcome in a variable

Type guard

bool TryGetCurrent(Point3DCollection.Enumerator e, ref bool finished, out Point3D cur) { cur = default; if (finished) return false; cur = e.Current; return true; }

Try / catch

try { var cur = e.Current; }
catch (InvalidOperationException) { /* enumerator exhausted; capture items inside the loop instead */ }

Prevention

Store the desired item in a local inside the loop, not via Current afterwards
Use foreach so Current is never read post-loop
Reset or re-create the enumerator before another pass

When it happens

Trigger: Accessing e.Current after a foreach or while(MoveNext()) loop finished; reading Current of an exhausted enumerator without Reset().

Common situations: Grabbing 'the last visited item' after loop exit; debugging code that reads Current post-enumeration.

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/8c900f4befabf9f8. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media3D/Generated/Point3DCollection.cs:873

            /// 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
        }
        #endregion

        #region Constructors

        //------------------------------------------------------

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