dotnet/wpf · error · InvalidOperationException

SR.Enumerator_NotStarted

Error message

SR.Enumerator_NotStarted

What it means

BitmapMetadataEnumerator's Current property (IEnumerable MoveNext/Current pattern) throws InvalidOperationException with SR.Enumerator_NotStarted when Current is accessed before MoveNext has ever been called. WPF metadata enumerators follow the standard .NET enumerator contract: there is no valid current element until iteration begins.

Solutions

  1. Call MoveNext() at least once and only read Current when it returns true.
  2. Replace manual enumerator code with a foreach loop, which handles MoveNext ordering automatically.
  3. Check enumerator state before accessing Current if you store the enumerator across calls.

Example fix

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

Strategy: validation

Validate before calling

if (enumerator is null) throw new ArgumentNullException(nameof(enumerator));
// track state before reading Current
bool started = false;

Type guard

bool CanReadCurrent(IEnumerator e, bool lastMoveNextTrue) => lastMoveNextTrue;

Try / catch

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

Prevention

When it happens

Trigger: Reading the Current property of a BitmapMetadata enumerator (e.g. foreach-variable misuse or manual enumerator use) immediately after calling GetEnumerator() without a prior MoveNext() returning true.

Common situations: Hand-written loops over BitmapMetadata query strings using IEnumerator<string> where the developer forgets the initial MoveNext(); porting COM/IWICMetadataQueryReader code that assumes a 'first element' is already current.

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/750c323b36c8677a. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/BitmapMetadataEnumerator.cs:126

        #endregion // Methods

        #endregion // IEnumerator interface

        #region Properties
        
        /// <summary>
        /// The current timeline referenced by this enumerator.
        /// </summary>
        public String Current
        {
            get
            {
                if (_current == null)
                {
                    if (!_fStarted)
                    {
                        throw new InvalidOperationException(SR.Enumerator_NotStarted);
                    }
                    else
                    {
                        throw new InvalidOperationException(SR.Enumerator_ReachedEnd);
                    }
                }

                return _current;
            }
        }

        /// <summary>
        ///
        /// </summary>
        void IDisposable.Dispose()
        {
            // Do nothing - Required by the IEnumerable contract.
        }

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