dotnet/wpf · error · InvalidOperationException

SR.Enumerator_NotStarted

Error message

SR.Enumerator_NotStarted

What it means

PathFigureCollection.Enumerator.Current throws InvalidOperationException with SR.Enumerator_NotStarted when Current is read before the first call to MoveNext(). The enumerator uses _index == -1 to mean 'not started' and refuses to return a Current value in that state.

Solutions

  1. Call MoveNext() at least once before reading Current.
  2. Use a foreach loop instead of manual enumerator handling so the protocol is enforced.
  3. Reset the enumerator (or get a new one) if it was consumed and you need to iterate again.

Example fix

// before
var e = figures.GetEnumerator();
var first = e.Current;
// after
var e = figures.GetEnumerator();
if (e.MoveNext())
{
    var first = e.Current;
}
Defensive patterns

Strategy: type-guard

Validate before calling

var e = figures.GetEnumerator();
if (!e.MoveNext()) return; // empty collection
ProcessCurrent(e.Current);

Type guard

bool TryGetFirst(PathFigureCollection c, out PathFigure first)
{
    var e = c.GetEnumerator();
    if (e.MoveNext()) { first = e.Current; return true; }
    first = null; return false;
}

Try / catch

try
{
    var value = enumerator.Current;
}
catch (InvalidOperationException)
{
    // enumerator not started; call MoveNext() first
}

Prevention

When it happens

Trigger: Accessing the Current property of a PathFigureCollection enumerator immediately after GetEnumerator() without calling MoveNext() first.

Common situations: Hand-written enumerator loops that forget the initial MoveNext; code that stores an enumerator and reads Current speculatively; misused LINQ replacements or manual foreach expansions.

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/766fd36c8288ddc1. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Generated/PathFigureCollection.cs:939

            /// <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 PathFigure 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 PathFigure _current;
            private PathFigureCollection _list;
            private uint _version;
            private int _index;
            #endregion
        }

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