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

Read Current only inside the loop, immediately after MoveNext() returns true

dotnet/wpf · error · InvalidOperationException

SR.Enumerator_ReachedEnd

Error message

SR.Enumerator_ReachedEnd

What it means

Model3DCollection's enumerator Current property throws InvalidOperationException(SR.Enumerator_ReachedEnd) when Current is accessed after MoveNext has returned false (i.e. the enumerator position is past the end, _index == -2). The WPF generated collection enumerators enforce strict access ordering: Current is only valid while positioned on an element.

Solutions

Read Current only inside the loop, immediately after MoveNext() returns true
Call Reset() before reusing an enumerator, or simply create a new one via GetEnumerator()
Prefer a foreach loop over manual MoveNext/Current code so the compiler enforces correct usage

Example fix

// before
var e = collection.GetEnumerator();
while (e.MoveNext()) { }
Console.WriteLine(e.Current); // throws
// after
foreach (Model3D m in collection)
    Console.WriteLine(m);

Defensive patterns

Strategy: try-catch

Validate before calling

bool canReadCurrent = enumeratorHasStarted && !enumeratorFinished; // track MoveNext results yourself

Type guard

bool CanReadCurrent(System.Collections.IEnumerator e, bool lastMoveNextResult) => lastMoveNextResult;

Try / catch

try { var cur = e.Current; }
catch (InvalidOperationException) { /* enumerator past end; re-enumerate */ e.Reset(); }

Prevention

Use foreach instead of manual MoveNext/Current loops
Never read Current outside an active loop iteration
Create a fresh enumerator for each pass instead of reusing

When it happens

Trigger: Accessing the Current property after a foreach loop has completed, or after calling MoveNext() until it returns false and then reading Current without calling Reset().

Common situations: Reusing a single enumerator object across multiple passes; storing the enumerator and reading Current after loop exit; hand-rolled iterator loops that forget to Reset() before reuse.

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/08198772d8b528f2. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media3D/Generated/Model3DCollection.cs:887

            /// 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
        }
        #endregion

        #region Constructors

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

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