dotnet/wpf · error · NotSupportedException

SR.UnsupportedTypeEncounteredWhenBuildingStgEnum

Error message

SR.UnsupportedTypeEncounteredWhenBuildingStgEnum

What it means

While building the storage enumerator, CompoundFileStorageInfo (StorageInfo) walks IEnumSTATSTG elements and maps each type to a StorageInfo or StreamInfo; encountering a STATSTG type that is neither STGTY_STORAGE nor STGTY_STREAM throws NotSupportedException with SR.UnsupportedTypeEncounteredWhenBuildingStgEnum. This guards against unknown/lock-only element types in the compound file.

Solutions

  1. Validate/repair the compound file by opening and re-saving it in the owning application.
  2. Skip broken elements by catching NotSupportedException around enumeration and continuing with the valid children.
  3. Enumerate via the native IStorage directly and filter on dwType yourself.
  4. Regenerate the container with the supported .NET Packaging writer.

Example fix

// before
foreach (var s in storageInfo.GetStorageInfos()) { ... } // throws NotSupportedException
// after
List<StorageInfo> storages = new List<StorageInfo>();
try { storages.AddRange(storageInfo.GetStorageInfos()); }
catch (NotSupportedException) { /* skip unsupported element types */ }
Defensive patterns

Strategy: try-catch

Validate before calling

// pre-validate container by opening it fully before enumerating
using var test = StorageRoot.OpenOnStream(stream, FileMode.Open, FileAccess.Read, null);
_ = test.GetStorageInfos().ToList();

Prevention

When it happens

Trigger: Enumerating a storage whose IEnumSTATSTG yields an element of an unexpected type (e.g. STGTY_LOCKBYTES or corrupt type bytes) via GetStorageInfos/GetStreamInfos or the child collections.

Common situations: Corrupt or hand-crafted compound files; files produced by third-party OLE writers containing lockbyte entries; bitwise file damage making the type field invalid.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/65ff372bc0a9bc79. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/System/IO/Packaging/CompoundFile/StorageInfo.cs:1357

                    if( desiredArrayType == EnumeratorTypes.Everything ||
                        desiredArrayType == EnumeratorTypes.OnlyStorages )
                    {
                        // Add reference to a storage to enumerator array
                        storageElems.Add(new StorageInfo(this, externalName));
                    }
                }
                else if( SafeNativeCompoundFileConstants.STGTY_STREAM == enumElement.type )
                {
                    if( desiredArrayType == EnumeratorTypes.Everything ||
                        desiredArrayType == EnumeratorTypes.OnlyStreams )
                    {
                        // Add reference to a stream to enumerator array
                         storageElems.Add(new StreamInfo(this, externalName));
                    }
                }
                else
                {
                    throw new NotSupportedException(
                        SR.UnsupportedTypeEncounteredWhenBuildingStgEnum);
                }

                // Move on to the next element
                safeIEnumSTATSTG.Next( 1, out enumElement, out actual );
            }

            core.validEnumerators[ desiredArrayType ] = storageElems;

            // Release IEnumSTATSTG
            ((IDisposable) safeIEnumSTATSTG).Dispose();
            safeIEnumSTATSTG = null;
        }

        Debug.Assert( null != core.validEnumerators[ desiredArrayType ],
            "We failed to ensure the proper array for enumeration" );
    }
}

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